Bulletin of the American Physical Society
APS March Meeting 2024
Monday–Friday, March 4–8, 2024; Minneapolis & Virtual
Session N00: Poster Session II (11:30am-2:30pm CST)Poster Undergrad Friendly
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Sponsoring Units: APS/SPS Room: Hall BC |
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N00.00001: POLYMER PHYSICS
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N00.00002: Machine learning enhanced CREASE method for Analyzing 2D Small Angle Scattering Profiles Sri Vishnuvardhan Reddy Akepati, Nitant Gupta, Arthi Jayaraman Understanding structural diversity in polymeric materials is a key step towards engineering new materials for various applications. One way to probe structures at varying length scales (nm to micron) is through small angle scattering (SAS); where a typical measurement provides as output the scattered intensity (I) vs. the magnitude of the wavevector (q) and azimuthal angle (Ɵ). To overcome some of the challenges researchers have in interpreting this two-dimensional I(q, Ɵ), especially for structures exhibiting anisotropy, we present a machine learning boosted ‘computational reverse engineering analysis for scatting experiments’ (CREASE) method. The chosen machine learning model, XGBoost, is trained to relate structural features (e.g., particle shapes and sizes, orientational order in particle arrangement) to the I(q, Ɵ) profile. Using the trained XGBoost model within the CREASE workflow, we accelerate the identification of structural features whose computed I(q, Ɵ) matches the input (experimental) I(q, Ɵ). This streamlined XGBoost-CREASE methodology eliminates traditional complexities in manual interpretation and provides an efficient and fast way to understand structural diversity in soft materials. |
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N00.00003: Effect of competing architectural asymmetries on the self-assembly of star copolymers Alfredo Alexander-Katz, Guillermo A Hernandez-Mendoza, Artem Petrov Self assembly of block copolymers is of interest in many areas of soft matter physics from fundamental studies to real-life applications. Here we explore the behavior of star copolymers with arms that are copolymers themselves, and that present architectural asymmetries, e. g. the volume fractions of the different chemical blocks in different arms is not conserved. By using self-consistent field-theoretic (SCFT) simulations and a self-driving in-silico lab platform we discover and characterize the transformations/morphologies occurring in this system as a function of the incompatibility parameter. We extend this results to more complex star copolymers, including janus stars. |
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N00.00004: A Machine Learning Approach for Describing Shear-induced Dynamics in Soft Particle Glasses Harsh Pandya, Patrick Cuddihy, Nazanin Sadeghi, Fardin Khabaz Soft particle glasses (SPGs) are deformable particles jammed at volume fractions beyond the random close packing of equivalent hard spheres. These athermal suspensions exhibit weak solid-like behavior at rest and a liquid-like flow above yield stress. Due to many factors affecting their properties, such as solvent viscosity, particle elasticity, and volume fraction, SPGs display fascinating shear-induced heterogeneous dynamics due to their ability to store and release internal stresses. In this study, we seek to understand the correlation between the structure and dynamics of SPGs using predictive machine learning (ML)-based methods. We employ linear regression and neural network models along with per-particle descriptors to predict the propensity of the particles to undergo heterogeneous dynamics. The accuracy of our predictions will be validated by comparing them directly to results obtained from three-dimensional particle dynamic simulations. ML model in conjunction with 3D simulations will be used to build relationships between the microstructure and localized yielding events in SPGs. |
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N00.00005: Coarse-Grained Artificial Intelligence for Design of Brush Networks Andrey V Dobrynin, Mohammad Vatankhah-Varnosfaderani, Sergei Sheiko, Anastasia Stroujkova We outline a design strategy based on synergistic combination of theoretical and artificial intelligence tools for encoding mechanical properties of brush networks with three architectural parameters: degrees of polymerization (DP) of network strands, nx, side chains nsc, and backbone spacers between side chains, ng. Implementing a two-layer feedforward artificial neural network (ANN), we take advantage of the coarse-grained representation of chemistry specific characteristics defined by monomer projection length l and excluded volume v, Kuhn length b of bare backbone and side chains, and architecture [nsc,φ=ng/(ng+nsc), nx] of brush networks and their equilibrium mechanical properties described by the structural shear modulus G and firmness parameter β. In our approach, a five-dimensional input vector [b/l,v/l3,φ,nscl/b,nxl/b], corresponding to a coarse-grained representation of network, is mapped into two-dimensional vector [Gv/β, β] representing network mechanical properties. ANN was trained on data sets for brush networks of poly (n-butyl acrylate), polyisobutylene and poly(dimethyl siloxane) strands and used for synthesis of networks with the nearly identical stress-elongation curves made with different monomers or strand architectures. |
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N00.00006: Mixed Ion-Electron Conducting Polymer Architectures for Energy Storage Applications Pratyusha Das, Alexandra Zele, Phong H Nguyen, Michael L Chabinyc, Rachel A Segalman Mixed ion-electron conducting polymers have garnered significant attention in recent years for applications in batteries, electrochemical transistors and many such electrochemical devices. Due to contradictory design rules for electron and ion conduction, the library of such mixed conducting polymers is small. While conjugated polymers with Li+-ion conducting oligoether side chains have previously shown mixed conducting ability, their ionic conductivity (∼10-7 S/cm) lags far behind their electronic counterpart ((∼10-1 S/cm). In this regard, our group has previously shown that cationic conjugated polyelectrolytes such as polythiophenes with alkyl side chains attached to imidazolium pendant units and bulky TFSI- counterions can lead to long-range polymer ordering and diffuse ion interactions resulting in high Li+ transport (∼10–4 S/cm at 80 °C) and electronic conductivity (∼ 10-4 S/cm). In this work, we have further engineered the polymer architecture to incorporate alkoxy side chains with imidazolium pendants to increase stability in the doped state, thereby further enhancing electronic conductivity and electrochemical stability. We observed that even with Br- counterions, before ion exchange with bulky TFSI-, bulk ionic conductivity is of the order of 10-3 S/cm at 80°C, while electronic conductivity was increased by several orders of magnitude, up to 10-2 S/cm upon vapor doping using HTFSI. This demonstrates considerable enhancement of mixed ion-electron conduction on incorporation of alkoxy side chains compared to alkyl side chains. Our current efforts are focused on measuring Li+ ion diffusion using PFG NMR, morphological investigation using GIWAXS and finally application as battery binders upon electrostatic compatibilization with an oppositely charged polymeric ionic liquid (PIL) which has also been previously established by our group. |
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N00.00007: Effective strategies for improving ionotronic sensory performance EUN JI HAN Pressure sensors detecting mechanical deformation are one of key components for wearable ionotronics. In this study, we propose an effective route to tune ion gel characteristics by adjusting pendant groups of ionic liquids. We created film-type ion gels very conveniently by one-pot photopolymerization. The ion gel films were carefully characterized and optimized. The ionotronic pressure sensors based on the optimized gels provided high sensitivity (~3.02kPa-1), wide detection range (~100 kPa), and excellent durability (~6,000 cycles). Their practicality was evaluated by fabricating unit cell arrays for sensory applications. |
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N00.00008: Multimodal Wearable Ionoskins Distinguishing Separately Recognition of External Stimuli Without Signal Crosstalk Jin Han Kwon Wearable ionoskins are one of the representative examples of the many useful applications offered by deformable stimuli-responsive sensory platforms. Herein, ionotronic thermo-mechano-multimodal response sensors are proposed, which can independently detect changes in temperature and mechanical stimuli without crosstalk. For this purpose, mechanically robust, thermo-responsive ion gels composed of poly(styrene-ran-n-butyl methacrylate) (PS-r-PnBMA, copolymer gelator) and 1-butyl-3-methylimidazolium bis(trifluoromethyl sulfonyl)imide ([BMI][TFSI], ionic liquid) are prepared. The optical transmittance change arising from the lower critical solution temperature (LCST) phenomenon between PnBMA and [BMI][TFSI] is exploited to track the external temperature, creating a new concept of the temperature coefficient of transmittance (TCT). The TCT of this system (-11.5% °C-1) is observed to be more sensitive to temperature fluctuations than the conventional metric of temperature coefficient of resistance. The tailoring molecular characteristics of gelators selectively improved the mechanical robustness of the gel, providing an additional application opportunity for strain sensors. This functional sensory platform, which is attached to a robot finger, can successfully detect thermal and mechanical environmental changes through variations in the optical (transmittance) and electrical (resistance) properties of the ion gel, respectively, indicating the high practicality of on-skin multimodal wearable sensors. |
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N00.00009: Achieving comparable power conversion efficiency of organic solar cells by using environment-friendly solvents Ushasri Mukherjee The primary challenge facing the contemporary world is the need for more reliable and replicable energy sources. Currently, the utmost crucial requirement for living in society is the availability of boundless energy resources. Extensive research has proved that solar energy is the most reliable and repeatable source. The inexhaustible energy source can be used to meet our energy requirements. Solar cells are devices that transform solar light into electrical power. Silicon solar cells are predominantly utilised worldwide among the many types of solar cells. However, much research is being conducted on organic solar cells, which differ from inorganic solar cells. Organic solar cells include both benefits and drawbacks. The primary benefits of organic solar cells are their affordability and the simplicity of their processing conditions. |
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N00.00010: Plasma Synthesis of 2D Layered SiC NCs with High PL QY Salim Thomas, Naif Saad Alharthi, Erik K Hobbie Silicon carbide nanocrystals (SiC NCs) with bright photoluminescence (PL) are of current interest for a range of potential applications, such as bioimaging, bio-photonics, and diagnostics and fabrication of optical nanodevices. Here, we use the liquid precursor tetramethylsilane (Si(CH3)4) for the plasma synthesis of two dimensional (2D) SiC NCs with exemplary surface emission. Through processing executed in an oxygen-shielded environment, we achieve PL quantum yields (QYs) approaching 70%. TEM/AFM on the colloid show NCs with lateral size ~ 5-10 nm and sub-nm thickness, with crystallinity and thickness confirmed by XRD and TEM. Raman spectra show no optical phonon splitting relative to the bulk, characteristic of 2D materials, and consistent with the layered structure of the flakes. FTIR shows that predominance of Si-OCH3 at the surface plays a major role in the enhancement of the photophysical properties in the over confined 2D SiC NCs. The results offer additional insight into the photophysical interplay of the nanocrystal surface, and quantum confinement. |
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N00.00011: Electrical Properties of Radical-containing Monomers and Their Application in Topochemically Polymerized Macromolecules Yun-Fang Yang, Baiju P Krishnan, Hyunki Yeo, Bryan W Boudouris Nonconjugated radical-based materials have emerged as compelling candidates for electrical conductors due to their stable open-shell sites. However, most of the research focus has remained on amorphous radical polymers, with limited attention paid to the impact of molecular packing on charge transport properties. Therefore, we designed, synthesized, and crystallized two nitroxide-based radical molecules, hexa-2,4-diyne-1,6-diyl bis((1-hydroxyl-2,2,6,6-tetramethylpiperidin-4-yl) carbamate) (TEMPO-DY-TEMPO) and 5-phenylpenta-2,4-diyn-1-yl (1-hydroxyl-2,2,6,6-tetramethylpiperidin-4-yl) carbamate (DY-TEMPO). With the potential of diynes for intrinsic highly ordered alignment through topochemical reaction, these molecules, with differing symmetries, were employed to evaluate the physical phenomena associated with electrical conductivity in single-crystal studies. DY-TEMPO, with its enhanced radical proximity (~4.838 Ǻ), shows an impressive electrical conductivity of ~91 S m−1 at ambient temperature with no doping and a magnetoresistance value of 140% at 10 K. Thus, open-shell small molecule single crystals were developed with superior charge transport capabilities through optimized packing of active radical moieties. Furthermore, these results afford valuable insights into the potential design of future crystalline polymers through topochemical polymerization for the next generation of nonconjugated radical electrical conductors. |
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N00.00012: Automating Simulations of Block Copolymers to Find Structural Features Using a Closed-Loop Optimization Process Jacob R Breese, Ting-Yeh Chen, Joel A Paulson, Lisa M Hall When performing molecular dynamics (MD) simulations with adjustable parameters, one may consider a grid of equally spaced values of the parameters to understand the entire parameter space. However, if the goal is to find a certain region of the space (e.g. conditions that optimize a property), the user may instead search by iteratively running a small number of simulations and then choosing where to continue the search based on knowledge of the system thus far. To increase the efficiency of such a process, we automate our simulations and apply a Bayesian Optimization (BO) algorithm to choose parameters in an unsupervised manner. We test our process by finding the coil-to-globule transition of amphiphilic block copolymer chains as a function of hydrophobic fraction and solvent quality. Specifically, we use a Dissipative Particle Dynamics (DPD) model bead-spring chain in solvent with a variable solvent-bead interaction strength. A few initial simulation runs are used to generate a coarse approximation of the radius of gyration function, then a manifold-crawling BO algorithm is applied to choose additional points to determine the extremum in its derivative. We will discuss how this coil-to-globule transition depends on hydrophobic fraction for di-, tri-, and tetra-block copolymers. |
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N00.00013: PSCF+: An Extended and Improved Open-Source Software Package for Polymer Self-Consistent Field Calculations of Block Copolymer Self-Assembly Juntong He, Qiang Wang We have extended the recently released C++/GPU version of PSCF1, an open-source software package for real-space self-consistent field (SCF) calculations of the “standard” model (i.e., incompressible melts of continuous Gaussian chains with the Dirac δ-function potential) for block copolymer self-assembly, to include various discrete chain models with finite-range interactions that are commonly used in molecular simulations, for example, the dissipative particle dynamics (DPD) model (i.e., compressible melts of discrete Gaussian chains with the DPD potential); this enables direct comparisons between SCF calculations and molecular simulations of the same model system, without any parameter-fitting, to unambiguously quantify the effects of fluctuations and correlations neglected by the former. We have also improved several aspects of PSCF1, making it much more suitable for efficient construction of accurate phase diagrams for block copolymer self-assembly. As an example, SCF calculations of the Frank-Kasper (FK) phases formed by conformationally asymmetric diblock copolymer melts based on DPD model are performed, and the comparisons with the SCF results based on the “standard” reveal the effects of model differences on the stability of FK phases. |
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N00.00014: Investigating the Interaction of Two Bottlebrush Polymer Grafted Nanoparticles: Effects of Stiffness and Grafting density of polymer Seoyeun Kim, Ji Woong Yu, YongJoo Kim Bottlebrush Polymer Grafted Nanoparticles (BPGNs) are synthesized to effectively control the nanoparticle within a polymer matrix and have important applications in nano-based optical materials, medical particles, and nano electronic devices. In this work, we studied the interaction between two BPGNs when one BPGN's chain approaches the core of another nanoparticle. To save simulation costs, an implicit solvent condition and coarse-grained model were adopted, and the stiffness of the backbone chain was controlled by the implicit solvent condition of the side chains. Under good solvent conditions and high grafting density, the simulation results show that the approach to the core was faster compared to the bad solvent and low polymer grafting conditions. Additionally, a steric repulsion region caused by osmotic pressure was found under the good solvent condition, causing chain separation. Finally, we conducted simulations to investigate the effect of the stiffness of the backbone chain by giving an angle potential to the backbone chain. Increasing the energy coefficient resulted in faster core approach and the effect of osmotic pressure was more pronounced. This study proposes more efficient ways to induce gelation when self-assembling BPGNs. |
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N00.00015: Thermodynamic Driving Forces of Coacervate Nanoparticle Assembly Emmit K Pert Synthetic and biological polymers that transport and deliver molecular cargoes in living systems self-organize, but multiple thermodynamic driving forces are often in play. Here we study tradeoffs between micelle formation and coacervation in a model copolymer system in an effort to determine the spatial organization of mRNA delivery nanoparticles. We use a fully fluctuating polymer field theory to simulate larger-scale behavior than is possible with particle-based methods. |
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N00.00016: Adsorption of pH responsive ampholytic ions into weak Polyelectrolyte brush: A simulation study Keerthi Radhakrishnan, Christian Holm Weak polyelectrolytic (PE) brush mediated protein adsorption has gained significant attention in the recent past. Especially beyond the isoelectric point, where a similar charge PE-protein attraction is seen. While, one plausible argument is the presence of low effective pH inside the brush, leading to subsequent charge reversal in the ampholyte protein. Other studies on patchy protein attributes it to the attraction of oppositely charged patches on protein surfaces and a counterion release force. To corroborate these further, we employ an explicit ion based molecular dynamic simulations to study a two phase weak PE brush system in contact with a reservoir consisting pH-responsive ampholytic entities. This simualtion framework accounts for both acid-base equilibria as well as the exchange of ions across the two phases within a grand canonical framework. Strong Donan partitioning of ions as well as the electrostatic effects together is seen to cause a significant shift in effective pH inside the brush, impacting the charge regulation and net uptake of adsorbing ampholyte ions. Insights from this study are extended to advanced models mimicking globular proteins, such as macroscopic particles with ionizable surface groups. Understanding charge regulation coupled with the structural arrangement of surface groups reveals intriguing facets of the protein adsorption mechanism under changing physiological conditions. |
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N00.00017: Bottom-Up Coarse-Grained Modeling of Sequence-Specific Polymers Daniela M Rivera Mirabal, Shawn Mengel, Sally Jiao, Evan Pretti, Audra J DeStefano, Rachel A Segalman, Scott Shell Molecular modeling offers direct insight into conformational landscapes, enhancing our understanding of sequence-structure relationships. In this work, we use sequence-specific peptoids as a platform for developing design rules for relating chemical sequence to polymer conformation. Polypeptoids are particularly useful in this context due to their lack of backbone hydrogen bonding, isolating the effect of sidechain chemical sequence on polymer chain shape. Moreover, they are routinely synthesized at gram scale, sequence-specifically, with hundreds of different side chain functionalities, allowing for detailed experimental investigation and validation. However, polypeptoid simulations encounter major sampling challenges due to the long-time scales associated with conformational transitions, which has greatly limited fundamental studies on broader peptoid chain shape effects and self-assembly behaviors. Recently, our studies of small polypeptoid systems with all-atom advanced sampling molecular dynamics revealed the local and global structure of short chains in response to their sequence patterning to be in excellent agreement with experiments. In this work, we develop a bottom-up coarse-grained peptoid model using the relative entropy approach to create a library of peptoid monomers suitable for studying CG models of a wide range of sequences in both long chain and self-assembly simulations. We validate the CG models with experimental end-to-end distance measurements measured from double electron-electron resonance (DEER) spectroscopy. Importantly, this CG approach allows for higher throughput simulations of peptoid chains and enables long and multi-chain studies not accessible with atomistic models. Moreover, this CG workflow enables the development of models that can be readily transformed into field-theoretic representations, facilitating exploration of larger length scales and phase behavior. |
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N00.00018: Dispersant Effect in Cathode Electrode Slurry System minyoung seo, AnSeong Park, Je-Yeon Jung, Seungtae Kim, Woojin Kim, Sangdeok Kim, Won Bo Lee, YongJoo Kim As technology development and demand for mobile devices increase, demand for secondary batteries as an energy source is rapidly increasing. Although many studies and innovative materials have been adopted in the industry, research on slurry systems is lacking compared to active materials. If polyvinylidene fluoride (PVDF) used as a binder for battery slurry is in the β phase which induces the crystallization of binders, the charging/discharging efficiency of the lithium-ion batteries (LiBs) is lowered, and problems such as capacity loss and charging time increase are caused. Therefore, although the current method of adding hydrogenated nitrile butadiene rubber (HNBR) to improve the rheological properties of the slurry by minimizing the β phase of PVDF has been commercialized, a detailed study on the relationship between PVDF and HNBR relationship at the atomic scale are not well-known. In this study, the effect of the HNBR dispersant on the crystal phase of the binder PVDF in the slurry system of a lithium-ion battery was analyzed using molecular dynamics (MD) simulation. In this system, n-methyl-2-pyrrolidinone (NMP) was used as the solvent. In the PVDF/NMP/HNBR system with various HNBR configurations, the β phase ratio of PVDF gradually decreased from 71.12% to 30.01% as the Acrylonitrile (ACN) contents of HNBR increased. It was found that the CN groups of HNBR interfered with the crystalline state of PVDF to make it amorphous. Through radial distribution function (RDF) Analysis, we found that the strong attraction between the HNBR nitrogen and the PVDF fluorine was the cause. When the ACN contents of HNBR were fixed at 33.9%, as the number of HNBR increased, HNBR suppressed the β phase, which is the linear conformation of PVDF. Through the analysis of the dispersant effect in the cathode material slurry system, we can develop a large-scale coarse-grained simulation platform for coating process in the future. |
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N00.00019: Linking polysulfamide design to morphology using molecular simulation and machine learning Jay A Shah, Aanish Paruchuri, Lalith Nagidi, Shizhao Lu, Arthi Jayaraman Polysulfamides are a new family of polymer that are analogous to polyureas with a sulfamide group in place of polyurea’s carbonyl group. Polysulfamides exhibit increased thermal stability, adjustable glass transition temperatures with changing polymer backbone structure, and degradability in green conditions (Chemical Science, 2020, 11, 7807-7812). To consider polysulfamide as a sustainable alternative for polyurea, there is a need for a fundamental understanding of how polysulfamide’s morphology and physical properties change with varying polysulfamide designs. In this poster, we will share our work linking polysulfamide morphology to changing design using molecular simulations and machine learning (ML). Our new coarse-grained polysulfamide model enables molecular simulations that complement experiments in our collaborators’ labs. The positional and orientational order of polymers in the simulation is compared to extent of crystallinity observed in experiments using X-ray diffraction, atomic force microscopy, wide-angle X-ray scattering, infrared spectroscopy, and differential scanning calorimetry. Using ML models that automate the quantification of crystallinity from experimental data will be useful to directly compare experimentally observed trends with simulation trends. |
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N00.00020: Cryogenic Studies of PL From Polymer Nanocomposites of 2D layered SiC NCs Naif S Alharthi, Salim A Thomas, Erik K Hobbie While the nature of photoluminescence (PL) relaxation in 2D layered vitrified colloidal silicon-carbide (SiC) nanocrystals (NCs) is still developing, efficient PL from SiC NC polymer nanocomposites has significant potential implications for new biolabeling and solar-collection technologies. In this study, we investigate the specifics of PL relaxation in photopolymerized off-stoichiometric polymer nanocomposites of 2D layered SiC NCs. In detail, tetra-functional thiol, tri-functional allyl, and a series of dodecyl-passivated colloidal 2D layered SiC NCs are used to create a series of thiol-ene polymer/nanocrystal composites. We explore their PL relaxation in the parameter space of emission wavelength, quantum yield, and temperature, concentrating on the observed changes in PL relaxation time upon cooling to cryogenic conditions. The nanocomposites exhibit air-stable blue emission, with our results providing physical insight into the nature of surface and impurity emission from these emerging materials. |
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N00.00021: A Novel Optical Absorption Method to Monitor Polymer Infiltration Inside a Bicontinuous, Nanoporous Gold Scaffold Chuyi Pan, Weiwei Kong, Rongyue Lin, Russell J Composto Polymer nanocomposites (PNC) have received much attention due to their wide ranging applications from tires to membranes. Creating PNCs with high loading remains a challenge because discrete nanoparticles tend to aggregate. In this work, we create high loading PNCs by fabricating polymer infiltrated nanoporous gold (PING). Ultraviolet-visible (UV-Vis) spectroscopy is used to monitor polymer infiltration in nanoporous gold (NPG). In this study, poly(2-vinylpyridine) (P2VP) is infiltrated into NPG that has a bicontinuous structure with ca. 50 vol% porosity and 75 nm pore diameter. Upon heating above its glass transition temperature, P2VP infiltrates inside the NPG, resulting in a plasmon resonance peak wavelength shift and absorption intensity increase. Simulations using discrete dipole approximation are employed to validate the accuracy and efficacy of UV-Vis spectroscopy in examining the PING formation. Infiltration time scales with molecular weight as M1.4, in agreement with previous spectroscopic ellipsometry findings. These studies provide a new fundamental understanding of polymer melt infiltration under confining conditions as well as guidelines for fabricating PNCs with loadings above 50 vol%. |
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N00.00022: Nanoparticle Diffusion as a Function of Polymer Molecular Weight and Bound Layer Dynamics Kaitlin Wang, Russell J Composto, Karen I Winey The bound layer is characteristic of attractive polymer nanocomposites (PNCs) and contributes to improved nanoparticle (NP) dispersion and nanocomposite processing. However, the dynamics of bound layer exchange with the matrix are challenging to probe due to the lack of contrast between the bound and matrix polymers. Here, we probe NP diffusion across a variety of NP sizes (alumina, silica) and poly(2-vinylpyridine) (P2VP) molecular weights using time-of-flight secondary ion mass spectroscopy (ToF-SIMS). With increasing Rg:RNP (~0.5 to 3), the mode of polymer diffusion transitions from core-shell to vehicle. The strength of NP-polymer interaction is tuned using PS-co-P2VP copolymers. Our findings confirm the bound layer has strong influence on NP diffusion and establish NP diffusion as a method for exploring bound layer dynamics in attractive PNCs. |
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N00.00023: Tailoring the Morphology of Polymer-Grafted Nanoparticle Composites – A Study of Film Thickness and Nanoparticle Loading Aria C Zhang, Kohji Ohno, Russell J Composto Polymer nanocomposites (PNCs) provide solutions to various applications due to their enhanced material properties. These properties are intrinsically correlated with the dispersion state of the nanoparticles (NPs), which depends on various materials parameters and processing conditions. Our study aims to understand the PNC morphology and dynamics by varying parameters such as film thickness, nanoparticle loading, and annealing temperature. This study investigated PNC films of silica nanoparticles grafted with poly(methyl methacrylate) within a poly(styrene-ran-acrylonitrile) matrix. Using AFM and TEM, we investigated the surface and bulk structures of the PNC films after annealing. Additionally, water contact angle measurement and ToF-SIMS were used to assess surface hydrophilicity and quantify surface excess of the NPs. Unique domain growth patterns were observed for films of different thicknesses when examined through scaling laws relative to annealing time. We also constructed a bulk morphology map dependent on film thickness and annealing duration. At reduced loadings, the NPs were found to segregate to the surface upon annealing, leading to distinct particle-rich and particle-poor zones. This study demonstrates the interplay between thermodynamics, dynamics, and confinement in PNC films. |
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N00.00024: Mechanically-assisted catalytic depolymerization of polyolefins Jon Bingaman, R Bharath Venkatesh, Jung Hyun Ahn, Samantha Ausman, Susannah L Scott, Lynn M Walker, Rachel A Segalman Various heterogeneous catalysts have demonstrated promising conversion of polyolefins to small molecules. However, due to the highly entangled nature of commercial polyolefins, bulk polymer diffusion is very slow in the melt phase. Thus, catalytic conversion of macromolecules remains a slow process at moderate temperature (200-300 °C). The inability of polymer chains to access most of the catalyst active sites embedded in catalyst pores limits the overall catalyst effectiveness requiring supplemental methods of chain cleavage. We propose the use of mechanical scission via melt-phase flow fields as a plausible mechanism to assist in C-C bond scission. Using a model polyolefin, poly(ethylene-alt-propylene), mechanical forces present in a common batch reactor are shown to induce appreciable chain cleavage in the absence of an active catalyst. Further, mechanical scission is enhanced by exchanging the batch reactor for a twin-screw compounder capable of reaching torque ~104 times higher than in batch. This system provides in situ “preprocessing” of polymer chains in tandem with a solid-acid catalyst to enhance depolymerization. Combining mechanical scission with catalytic reactions will increase efficiency of reactions, alleviate mass transfer constraints, and reduce energy demand. |
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N00.00025: A low environmental impact emulsion process as an alternative to the conventional recycling methods of plastic wastes Simin Xia, Wenhao Qin, H Daniel Ou-Yang Conventional plastic recycling by melting or burning costs energy and produces secondary contamination. This paper presents a facile and low-energy-impact recycling procedure by converting single-use plastics into colloidal polymer nanoparticles. In this procedure, solutions of these polymers in organic solvents were first made into stable emulsions in surfactant solutions. Removing the solvent from the emulsion then rendered a stable suspension of colloidal nano polymer particles. Although the principles are simple, technical challenges of conducting the procedure abound. Shear-induced emulsion with its process dictated by the onset of the Taylor instability is governed by a few physical parameters, including the viscosity of the polymer solution, the interfacial tension between the polymer solutions and the aqueous phase, and the shear rate; choices of solvents and surfactant are critically important. This study examined the effects of the above control parameters on the final particle sizes, size distribution, solid contents, times required to remove solvents from the emulsion, and the long-term stability of the final latex suspensions. Energy cost, including shear and recovery of the solvents for reuse, will be estimated for comparison with that of conventional methods for recycling similar polymers. |
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N00.00026: Macromolecular composites as physical analogues of biomatter plastics: insights into bonding motifs, microstructure and bulk mechanical properties Eleftheria Roumeli, Ian R Campbell, Ziyue Dong, Paul Grandgeorge, Ella Lee, Kayla Sprenger Innovative and sustainable technologies intended to prevent the harmful effects of sourcing, manufacturing, and disposing of synthetic plastics are rarely both biobased and biodegradable. Many biodegradable plastics will in fact not fully decompose in natural settings and despite the best recycling efforts, the most significant portion of the plastic produced annually escapes into the biosphere. In an effort to create a fully biobased and backyard-compostable plastic alternative, we recently reported a bioplastic formulation composed only of spirulina biomass, without the need for extraction or other energy-intensive treatments. The application of heat and pressure transforms the biomass into a rigid, thermoformable and backyard compostable biomatter plastic with mechanical performance rivaling polystyrene and polylactic acid. In this work, we investigate the mechanism governing the self-bonding of spirulina during thermomechanical processing by creating a representative analogue for biomatter plastics. We vary the ratios of pure carbohydrates, lipids, and proteins are physically combined and subject the produced biopolymer composites to heated compression molding to form materials with composition emulating that of our algal bioplastics. The effect of the varying macromolecular composition, and the contribution of each class of macromolecule to the polymer morphology and mechanical properties of the formed biomatter analogues are evaluated by mechanical testing and scanning electron microscopy (SEM). The varying ratio of protein to carbohydrates is utilized to compare the mechanical performance of biomatter analogues to several algal species. The bonding mechanism of the biomatter analogues is first assessed qualitatively during sequential reprocessing to isolate contributions of dynamic bonding. Fourier transform infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS) are then utilized in combination with molecular dynamic (MD) simulations to quantitatively measure both secondary and primary bonding interactions between different macromolecular components of the analogue composites and a mechanism is proposed for self-bonding in biomatter plastics. |
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N00.00027: Incorporation of Long-Lived Interactions into Metal-Ligand Coordinating Polymer Electrolytes to Improves Bulk Mechanical Properties James Bamford, Ben Pedretti, Leo Gordon, Seamus D Jones, Nathaniel A Lynd, Raphaële J Clément, Rachel A Segalman Next-generation Li batteries require solid state electrolytes that decouple Li+ transport from bulk mechanics. We demonstrate that these properties can be separated by blending a metal-ligand coordinating polymer (MCP) with two types of metal cation salts, such that each salt independently tunes mechanics and ion transport via their interactions with the polymer ligand. Specifically, a polyether-based MCP with one type of ligand, imidazole (Im), can effectively decouple Li+ conductivity from bulk mechanics by mixing with Li+ and Ni2+ salts. Li+ has weaker ML interactions and diffuses rapidly. Ni2+ salt has stronger ML interactions and forms a dynamic network. A unique rheological plateau appears in the mixed-salt MCP that increases the storage modulus by over two orders of magnitude, from 0.014 MPa to 1.907 MPa. Dynamic Ni-Im crosslinks inhibit chain diffusion at larger length scales, while local Li+ hopping dynamics are only moderately stiffened. Thus, while introduction of Ni2+ salts to PEO-PIGE reduces Li+ conductivity by a factor of 2.6, from 9.8 to 3.7 *10-6 S/cm at 90 °C, bulk mechanics are significantly improved by a factor of 135. |
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N00.00028: Hydroxide Solvation and Transport in a Quaternized Precise Polyethylene William F Drayer, Karen I Winey, Amalie L Frischknecht Better understanding of the transport properties of anion exchange membranes (AEMs) is necessary to develop fuel cells with performance on par with more well-known proton exchange membranes (PEMs). Motivated by recent work on precise polyethylene-based PEMs synthesized by ring-opening metathesis polymerization (ROMP), we have developed an atomistic model for a precisely quaternized polyethylene with hydroxide counterions. We perform molecular dynamics simulations to establish the thermal properties and nanoscale morphology of the polymer at various hydration levels. We also use a reactive hydroxide model to more accurately determine hydroxide solvation and transport within the water channels. This work will facilitate and complement the design of new fluorine-free AEMs with competitive conductivities and mechanical properties. |
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N00.00029: Ionic Conductivity in Solvent-Swollen Surfactant-Like Multiblock Copolymer Thin Films Benjamin T Ferko, Benjamin Ketter, Zhongyang Wang, Paul F Nealey, Karen I Winey Previously, bulk samples of multiblock copolymers consisting of alkyl blocks of a fixed length (x) strictly alternating with polar blocks containing lithium sulfonate groups (PESxLi) form layered morphologies at room temperature. Selectively swelling the polar domains of these multiblock copolymers with DMSO increased the ionic conductivity by 10^4 while maintaining the layered morphology in the bulk. To reduce the role of morphological defects (i.e. grain boundaries) on the conductivity measurements, this study fabricates well-aligned thin films by spin coating and uses interdigitated electrodes to measure Li conductivity. Thin films of PESxLi spontaneously form layered morphologies aligned parallel to the substrate, such that the interdigitated electrodes measure the in-plane conductivity. We report on our progress towards measuring the conductivity of solvent swollen, aligned layers of PESxLi thin films. Custom fabricated solvent chambers permit both grazing incidence X-ray scattering and electrochemical impedance spectroscopy measurements under controlled solvent vapor environments at temperature. These experiments facilitate direct comparisons to all atom molecular dynamics simulations and promise to improve the understanding of how solvent impacts ionic conductivity in nanostructured single-ion conducting polymers. |
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N00.00030: Poster: Elucidating nanoparticle reinforcing effects through low-volume chemical coupling as explored by coarse-grained molecular dynamics Yawei Gao, Nihal Kanbargi, Joshua T Damron, Logan T Kearney, Jan Michael Carrillo, Jong Keum, Michael Toomey, Bobby Sumpter, Amit K Naskar The addition of linker molecules with varying topology and stoichiometry into a carbon nanotube (CN)-reinforced polymer composites exhibits pronounced morphological differences and resulting rheological properties compared to CN-reinforced only controls. The underlying mechanism of action is complex because the mesoscale properties evolve over a broad range of interrelated lengths and time scales. These originate at the local structure of the crosslinking junction, extending into the segmental motion in the Kuhn length regime and finally influencing the large-scale diffusive motions proportional to the radius of gyration. In this study, we present an easily scalable approach to elucidate the effect of linker topology and stoichiometry on the segmental dynamics and bulk properties in a covalently bonded CN polymer composite. We performed a series of coarse-grained molecular dynamics (CGMD) simulations to investigate the morphological and rheological performance of polymers in response to linker topology and crosslink reactions. Our CGMD results indicate that the degree of matrix phase separation is positively correlated with polymer segmental diffusivity, which can be limited through increasing linker rigidity and cross-linking. The CGMD results, which agree well with experimental measurement, can provide guidelines for the a priori design of CN-reinforced composite materials. |
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N00.00031: Mechanically Tough and Ionically Conductive Solid Polymer Electrolytes for Precise Motion Monitoring Applications Minsu Kim, Jeong Hui Kim, Dong Hyeon Park, Keun Hyung Lee Flexible gel electrolyte materials, as promising candidates for the next generation of quasi-solid electrolytes in electrochemical devices, face two formidable challenges: low mechanical toughness and insufficient ionic conductivity. To overcome these hurdles, diverse methods for solidifying ionic liquids and fabricating mechanically robust and ionically conductive gel electrolytes have been proposed. In this study, we developed physically crosslinked ion gels by the phase separation of a semi-crystalline structure of poly(vinyl alcohol) (PVA) in an ionic liquid. In the PVA ion gels, phase-separated crystals serve as network junctions. When mechanical stress is applied, the non-covalent bonds formed among polymer chains dissipate a substantial amount of energy. The resulting ion gels exhibited outstanding mechanical properties, with an extremely high toughness of ~46.24 MJ m-3 and remarkable stretchability of ~2135%. Moreover, the ion gels possessed excellent electrochemical performance, boasting a high ionic conductivity of approximately 20 mS cm-1 and maintaining stable electrochemical windows of approximately 3 V. These ion gels were successfully employed as stretchable strain sensor and the devices exhibited outstanding linearity, sensitivity, and operational durability. |
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N00.00032: Effect of Corona Block Asymmetry on Chain Exchange in Triblock Copolymer Micelles Taehyoung Kim, En Wang, Joanna M White, Frank S Bates, Timothy P Lodge Chain exchange kinetics in block copolymer micelles are determined primarily by the interaction parameter (χ) and the degree of polymerization of the core block (Ncore). Micelle chain conformation, determined by the block copolymer architecture, can significantly impact the kinetics. In this research, we investigated the effect of an asymmetric ABA′ architecture on chain exchange dynamics in triblock copolymer micelles. The triblock copolymer had a constant length polystyrene (PS) middle block, but different lengths of two poly(ethylene-alt-propylene) (PEP, PEP′) end blocks. Using time-resolved small-angle neutron scattering (TR-SANS), we compared the chain exchange kinetics for spherical micelles containing diblock, symmetric, and two asymmetric triblock copolymers prepared in squalane, a PEP-selective solvent. As the asymmetry parameter (r) increased, the rate of chain exchange accelerated tenfold from the diblock (r = 0) to asymmetric (0 < r < 1) and to a symmetric triblock copolymer (r = 1). Possible reasons for this behavior will be discussed.[1] Our work sheds light on the relationship between polymer architecture and micelle dynamics, thereby contributing to a better understanding for practical applications. |
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N00.00033: Effect of sulfonation level on the morphology, local structure, and proton conductivity of hydrocarbon-based random copolymers Sol Mi Oh, Courtney Leo, Emily Grumbles, Justin G Kennemur, Karen I Winey Although perfluorosulfonic acid polymers are widely used proton-exchange membranes, the economic and environmental disadvantages arising from fluorine have stimulated interest in hydrocarbon-based polymers. In previous work, we studied a linear polyethylene with a phenylsulfonic acid pendant group precisely on every fifth carbon and found the proton conductivity to exceed 0.1 S/cm above 70% relative humidity at 40 °C. To improve the precessability and mechanical properties of this polymer, this study explores lower sulfonation levels. Using X-ray scattering, FT-IR, pulse-field gradient NMR, electrochemical impedance spectroscopy, we determine the nanophase separation behavior of these polymers, the local chemical state and diffusion coefficient of water and the proton. A moderate reduction in sulfonation level enhances the mechanical toughness of while maintaining high proton conductivity. We attribute this high proton conductivity to the nanoscale morphology of percolated water channels in the membranes containing bulk-like water. |
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N00.00034: Counterion Size and Polarity Effects on Ionomer Dynamics Grace Sasko, Chathurika J Kosgallana, Gary S Grest, Dvora Perahia Numerous studies have shown that clustering of ionizable polymers controls the structure and dynamics of these macromolecules and consequently affects their properties. The clustering process is impacted by several factors, among them polymer topology and electrostatic interactions. With the goal of understanding the interrelation between clustering and polymer dynamics, the current study uses atomistic molecular dynamics (MD) simulations to probe the effects of counterion size and polarity on the dynamics of polymer melts using polystyrene sulfonate in the ionomer regime with sulfonation fraction f=0.09, below its entanglement length. The counterion chosen is N R4+ with R=H or CH3, varying the ratio of CH3:H affecting the size and the polarity of the cation. The systems were built in Biovia, Molecular Studio, and ran in LAMMPS and GROMACS. The static and dynamic structure factors were calculated and correlated with the characteristics of the ionic clusters. We find that this series of counterions significantly modifies the cluster size and shape in comparison to small inorganic cations such as Na+, impacting the structure and dynamics of the melts. The structure of the melts as the counterion is varied will be first discussed followed by introducing the dynamic structure factor S(q,t) and mean square displacement studies that together capture the motion of the polymers on multiple length scales. |
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N00.00035: Scaling Theory of Polymer Solutions: Viscosity, Chain Self-diffusion, and Osmotic Pressure Ryan Sayko, Andrey V Dobrynin Understanding properties of polymers in solutions remains one of the fundamental problems of polymer science. We applied a scaling approach based on the relationship between the solution correlation length ξ=lgν/B and the number of monomers g per correlation volume to analyze viscosity, chain self-diffusion coefficient, and osmotic pressure of charged and neutral polymers in solutions. The B-parameters and scaling exponent ν are determined by the solvent quality for the polymer backbone and type and strength of monomer-monomer interactions at different length scales. In our analysis of dilute and semidilute solution regimes, we highlight differences in the B-parameters obtained from solution viscosity, chain self-diffusion, and solution osmotic pressure. The extension of this approach to the entangled solution regime allows us to obtain the chain packing number and complete the set of parameters that describe dynamics of polymers in solution. This method is implemented to characterize the statics and dynamics of charged and neutral polymers in solutions. |
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N00.00036: Investigate Molecular Bottlebrush Conformation and Aggregation Status Under Different Solvent Quality Sidong Tu, Chandan K Choudhury, Michaela Giltner, Igor Luzinov, Olga Kuksenok Molecular bottlebrushes (MBBs) could be used as enzyme stabilizer, oil-repellent film modifier, polymer blend compatibilizer and so on. The implementation of these applications is owing to the control of MBB aggregation process and cluster morphologies. In this work, we focused on the effects of solvent quality on the aggregation process of MBBs. With Dissipative Particle Dynamics approach, we characterize the conformations of the MBBs in the limit of infinite dilution (single MBB) and average size of agglomerates containing multiple MBBs in solutions. We compare the conformation and aggregation status and probe three cut-off criteria used to identify MBB clusters. Using these criteria allows one to correlate the agglomeration status of MBB in various solvent qualities. |
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N00.00037: Ionic Conductivity Measurements of Single-ion Solid Copolymer Electrolytes based on Oxanorbornene Monomers Dean A Waldow The need for energy storage both in mobile as well stationary applications continues to grow. Safety issues of lithium-ion batteries have prompted work on polymer-based electrolyte materials with added lithium salts to address flammability but these typically suffer from lower ion conductivity due to ion coupling to polymer dynamics. The resulting ion conductivity of these materials is from both anions and cations where anion conductivity can be a hinderance which has prompted research into single-ion polymers. This report details the synthesis of oxanorbornene-based copolymers where one repeat unit has an oligomeric ethylene oxide (OEO) side chain and the other has a side chain with a sulfonimide type anion and lithium cation (TFSI). These copolymers are synthesized using a Grubbs catalyzed ring-opening metathesis polymerization reaction with varying monomer compositions. The TFSI anion is incorporated in the monomer either before polymerization (graft-through) or after polymerization (graft-to) both via a click reaction. By increasing the OEO content, the glass transition temperature can be lowered although resulting in a lower lithium content. The conductivities of these single-ion copolymers have been measured as a function of temperature using electrochemical impedance spectroscopy. The results demonstrate increased conductivity with decreased glass transition temperature despite lower TFSI content. |
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N00.00038: Hierarchical Dynamics of Polymer/Molecular Nanoparticles Hybrid Systems Huiming Xiong Fundamental understanding of the effects of the nanoparticles on chain conformation and dynamics of the polymers in hybrid polymer systems is interesting in both academic and industrial fields. Herein, the hierarchical dynamics of non-sticky polyhedral oligomeric silsesquioxane molecular nanoparticles (MNPs) tethered type-A polymer, poly(1, 2-butylene oxide) (PBO), and the PBO/MNPs nanocomposites have been studied. Non-crystalline and dielectric "invisible" MNP was specially designed to ensure its miscibility with PBO matrix. The chain dimension and dynamics of PBO in the nanocomposites have been investigated in broad frequency and temperature windows by utilizing broadband dielectric spectroscopy and rheology. The confinement, solvent and filler effects in this type of non-sticky nanocomposite model system have been discussed. Segmental and chain dynamics of PBO tethered with MNPs have been also investigated experimentally by a combination of broadband dielectric spectroscopy, rheology, and pulsed-field-gradient nuclear magnetic resonance techniques, to provide a fundamental understanding of the effects of chain ends and topology on the hierarchical dynamics of polymers. |
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N00.00039: Poster: Multilayer hydrogel microcubes: Effects of templating particle morphology on cubic hydrogel properties Daniel Inman, Veronika Kozlovskaya, Pavel Nikishau, Sarah Nealy, Eugenia Kharlampieva Non‐spherical stimuli‐responsive polymeric particles have shown critical importance in therapeutic delivery. Herein, pH‐responsive poly(methacrylic acid) (PMAA) cubic hydrogel microparticles are synthesized by crosslinking PMAA layers within PMAA/poly(N‐vinylpyrrolidone) hydrogen‐bonded multilayers templated on porous microparticles. Herein, the effects of template porosity and surface morphology on the PMAA multilayer hydrogel microcube properties are investigated. We found that the hydrogel structure depends on the template's calcination time and temperature. The pH‐triggered PMAA hydrogel cube swelling depends on the hydrogel's internal architecture, either hollow capsule‐like or non‐hollow continuous hydrogels. The loading efficiency of the doxorubicin (DOX) drug inside the microcubes analyzed by high‐performance liquid chromatography (HPLC) shows the dependence of the drug uptake on the network structure and morphology controlled by the template porosity. Varying the template calcination from low (300 °C) to high (1000 °C) temperature results in a 2.5‐fold greater DOX encapsulation by the hydrogel cubes. The effects of hydrogel surface charge on the DOX loading and release are also studied using zeta‐potential measurements. This work provides insight into the effect of structural composition, network morphology, and pH‐induced swelling of the cubical hydrogels and may advance the development of stimuli‐responsive vehicles for targeted anticancer drug delivery. |
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N00.00040: Poster: Controlling mechanical properties of poly(methacrylic acid) thin multilayer hydrogels via hydrogel internal architecture Veronika Kozlovskaya, Maksim Dolmat, John F Ankner, Eugenia Kharlampieva We report on altering the mechanical behavior of ultrathin poly(methacrylic acid) (PMAA) multilayer hydrogels by changing the network's internal organization. The hydrogels were synthesized by cross-linking PMAA layers in poly(N-vinylpyrrolidone) (PVPON)/PMAA hydrogen-bonded multilayers prepared by dipped or spin-assisted (SA) layer-by-layer assembly using sacrificial PVPON with molecular weights of 40,000 or 280,000 g mol−1. The effect of PVPON molecular weight on hydrogel stratification, swelling, and hydration was assessed. We found that hydrogel swelling, the number of water molecules associated with the swollen hydrogel, and water density within the SA PMAA hydrogels can be controlled by choosing the molecular weight of PVPON. With similar cross-link densities, greater swelling and hydration at pH>5 were observed for SA PMAA hydrogels synthesized using higher-Mw PVPON. The enhanced swelling of the SA hydrogels resulted in softening with a lower Young’s modulus at pH>5. A twice greater softening of the SA PMAA hydrogel than that prepared by dipping was observed, with Young’s modulus values decreasing to tens of megapascals in pH > 5 solution. Unlike simply changing bulk hydrogel cross-link density, programming polymer network architecture enabled selective modulation of the cross-link density within hydrogel strata, and polymer chain intermixing through hydrogel stratification controls the internal architecture, hydrogel swelling, and network mechanical response. |
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N00.00041: Cosolvent incorporation tunes the nanostructure formation and thermal responsivity of aqueous PNIPAM/silyl methacrylate copolymers Jason D Linn, Fabian A Rodriguez, Michelle A Calabrese Polymers functionalized with inorganic silane groups have been used in a wide range of applications due to the silane reactivity. Stimuli-responsive polymers in these hybrid systems can be used for applications including sensing and optical coatings. Of particular interest is the thermoresponsive poly(N-isopropyl acrylamide) (PNIPAM) functionalized with 3-(trimethoxysilyl)propyl methacrylate (TMA), which has demonstrated unique aqueous thermal and optical responses. We previously showed that localizing the TMA in blocky domains led to the formation of uniform structures above the cloud point temperature, in comparison to disperse aggregates from random copolymers. Blocky localization also led to greater thermal cyclability than in random copolymers. Here, we investigate the role of solvent species and content on the size and dispersity of structures formed above the cloud point temperature in blocky-functionalized and random copolymers. Mixtures of solvents can introduce additional phase transitions and alter the phase boundaries based on temperature and composition. Cosolvent incorporation alters the aggregation of NIPAM/TMA copolymers, changing size and dispersity. Additionally, the optical response and cyclability depends on the copolymer composition and the cosolvent content. Cosolvent incorporation thus increases the versatility of inorganic-functionalized responsive polymers by providing a simple way to tune the structure size and response, leading to distinct applications. |
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N00.00042: Rate-dependent thermotropic phase transitions in liquid crystalline oligomers Emily C Ostermann, Chun Lam Clement Chan, Shawn M Maguire, Emily C Davidson Thermotropic liquid crystals (LCs) undergo temperature-dependent phase transitions between the isotropic, liquid crystalline, and crystalline states. However, metastable states are often only accessible at fast cooling rates that kinetically limit the transition from the isotropic to the equilibrium state. In this study, we synthesized monodisperse liquid crystalline oligomers by combining two different mesogens in varying sequences via iterative exponential growth synthesis using alkyne-azide click chemistry. These oligomers exhibit highly rate-dependent LC phase transitions, which we characterized through thermal, optical and X-ray scattering methods under targeted temperature ramp rates and annealing protocols. Precisely defining the conditions at which LC phases are accessible and stable (or metastable) allows us to tailor processing and chemical structure for targeted applications. |
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N00.00043: Probing Hydration Changes of Perdeuterated Poly(N-isopropylacrylamide) Across the Demixing-Transition with Vibrational Spectroscopy Alfons Schulte, Dharani Mullapudi, Alec Nieth, Nicolas Harms, Christopher Bennett, Dirk Schanzenbach, André Laschewsky, Christine Papadakis Replacing hydrogen with deuterium can have a profound effect on the phase behavior of biological and synthetic polymers. We investigate concentrated aqueous solutions of perdeuterated poly(N-isopropylacrylamide) (PNIPAM-d10) employing Raman scattering and infrared absorption spectroscopy. In comparison to PNIPAM the cloud point temperature increases by several degrees in PNIPAM-d10. The C-D vibrational bands of the alkyl groups are shifted to lower frequencies by a factor of 1.4 as expected for the isotope effect. In variable temperature experiments we observe an abrupt red-shift of the peak frequencies of the C-D bands at the demixing transition similar to those of the C-H bands in PNIPAM. These frequency shifts may be attributed to dehydration of the polymer chains at their coil-to-globule transition. |
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N00.00044: Elasto-magnetic Jumping Gels: Magnetic Latch-controlled Performance Xiaona Xu, Alfred J Crosby, James J Watkins Latch-Mediated Spring Actuation (LaMSA) drives the outstanding performance of many living organisms, including mantis shrimp and trap-jaw ants, which can generate high power motion without relying upon chemical reactions. In LaMSA systems, latches help to store and suddenly release elastic energy, allowing elastic recoil to dictate the power-amplified motion. A latch mechanism commonly found in natural, as well as engineered systems, is an elastic snap instability. While efficient, minimal feed-forward control can be realized with conventional snapping-based LaMSA systems. Here, we introduce a snapping soft gel device, in which the onset of the snap-through instability is mediated by a magnetic field. We fabricated disk-shaped swollen gel composites with dispersed magnetic particles. As the gels deswell, elastic internal forces develop and are resisted by an external magnetic field. Upon removing the magnetic field, the accumulated elastic energy is immediately released, driving a power-amplified snap-through instability. We present measurements that relate elastic energy storage and magnetic field dynamics to kinetic energy release in the snap-through deformation. |
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N00.00045: How does gelation impact the mechanical properties of polymer networks? Insights from polymer mechanochemistry Aaliyah Z Dookhith, Gabriel E Sanoja Polymer networks that sustain large reversible deformations are widespread in engineering, biomedical, and electronic applications. At high temperatures or solvent concentrations, these materials are excessively brittle due to negligible energy dissipation in the vicinity of cracks. Recently, this issue was resolved by Gong and co-workers by embedding a stiff, and pre-stretched polymer filler network within a soft and extensible polymer matrix network. Yet how the molecular architecture of these filler and matrix networks ultimately dictates the macroscopic fracture toughness remains unknown. |
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N00.00046: Elastomers of Oligocellulose Derivatives with Tunable Structures and Properties Howard Wang, Feng Jiang, Shuaishuai Chen, jiajun feng, Robert M Briber Oligocellulose (OC) with low polydispersity indices has been produced through acid-assisted hydrolysis of long cellulose chains in concentrated phosphoric acid at elevated temperatures. A series of OC-graft-poly(isobornyl methacrylate-random-n-butyl acrylate) [OC-g-P(IBOMA-r-BA)] elastomers have been synthesized via activators regenerated by electron transfer for atom transfer radical polymerization (ARGET ATRP). Tunable molecular architectures and phase morphologies structure and corresponding mechanical properties have been demonstrated. The synergistic behaviors of physical and chemical crosslinking networks are responsible for the unique mixture of elasticity and plasticity and the evolution of hysteresis in cyclic deformation. |
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N00.00047: Self-assembly and structural relaxation in 'patch-clasping' nanoparticles Ahyoung Kim, Kireeti Akkunuri, Chang Qian, Lehan Yao, Kai Sun, Zi Chen, Thi Vo, Qian Chen Polymer-grafted ‘patchy’ nanoparticles (NPs) can self-assemble into open network structures, making them great building blocks for tunable metamaterials. However, a fundamental understanding of the underlying driving forces remains elusive. Here, we combine simulation and experiments to study the assembly dynamics of a model system of triangular gold nano-prisms functionalized with polystyrene-polyacrylic acid block copolymers (PS-b-PAA). We show that inter-NP bonds formed between interacting polymeric patches are longitudinally robust and rotationally flexible. Scaling theory reveals that inter-NP bond formation is driven by chain reorganization between interacting patches. This enables the development of a coarse-grained model that reproduces experimental dynamics of network chains formed from multiple NPs. Simulations reveal that the network’s rotational relaxation, and therefore reconfiguration, is influenced by chain architecture and relative bond orientations between NPs. Our results suggest that tuning the relative orientations between patchy-NP during bond formation can provide a powerful handle for controlling the dynamical responses of reconfigurable nanomaterials. |
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N00.00048: Role of Processing and the Air-Polymer Interface on Crystallization of Poly(3-hexylthiophene) Jesse L Kuebler, Tucker Loosbrock, Joseph Strzalka, Lucia Fernandez Ballester Conjugated polymers—plastics capable of charge transport—are promising candidates for electronic devices such as field effect transistors, solar cells, and flexible sensors. In thin films, interfaces (such as the air-polymer interface) are known to play an important role in structure formation and final device properties, but the exact relationship is not well understood. To understand how a free surface interface affects morphology, orientation, and final properties across the thickness of P3HT (a model conjugated polymer) thin films, this study combined in-situ UV-vis spectroscopy and grazing incidence wide angle X-ray scattering (GIWAXS). A two-step crystallization process was revealed: first, surface-induced highly edge-on oriented spherulite-like structures formed in a ~20 nm layer at the air-polymer interface at T ~25 °C higher than the bulk crystallization temperature (TC,BULK) regardless of the film thickness. Then, the remainder of the film crystallized near TC,BULK with orientation that depended on film thickness. Overall, the results demonstrate that the air-polymer interface has a significant effect on the crystallization and final orientation of P3HT which is expected to have large implications for device performance. |
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N00.00049: Role of ring-size and side-chain length in artificial water channel permeability Tyler J Duncan, Harekrushna Behera, Paul R Irving, Nico Marioni, Harnoor S Sachar, Meron Y. Tadesse, Zidan Zhang, Everett S Zofchak, Manish Kumar, Venkatraghavan Ganesan Membranes are an integral part to the water-energy nexus and produce approximately 142 billion liters of desalinated water per day. A common trade-off observed in reverse osmosis membranes is an exchange between permeability and ion rejection (>99%). One such solution to overcome this upper bound is inspired by biological membranes that display high rejection and high permeability. Synthetic transmembrane channels mimic the function of aquaporin protein channels by promoting one-dimensional water transport and selectively transporting water via angstrom scale pores. We investigate one such synthetic channel architecture, ligand-appended pillarene, to evaluate how design parameters within the channel chemistry, such as channel ring-size (m=5,6), appended-ligand length (n=4,6,8), and appended chemistry, impacts the permeability of these synthetic channels. |
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N00.00050: Ion transport in weak polyelectrolyte membranes at varying external pH Yongha Kim, Ralph H Colby, Hee Jeung Oh Charged polymer membranes are of great interest in various applications, ranging from environment, energy, and health. Understanding of ion transport in charged polymer membranes is critical to the advancement of technologies related to polymer electrolytes in batteries, water purification, critical element extraction, environmental remediation, and medical isotope purification. Here, we designed a systematic library of weak polyelectrolyte membranes based on polyacrylic acid (PAA). A series of polyacrylic acid (PAA) based polymer networks were synthesized with varied charged group contents and controlled water swelling. By adjusting external pH, the number of sodium counter cations dissociated and condensed on the polymer backbone can be systematically changed, leading to different ion transport and dielectric properties in the polymers. We evaluated ion and water transport properties (solubility, diffusivity, and permeability) in the resultant polymer membranes. These transport properties are correlated with dielectric properties in the polymers via dielectric relaxation spectroscopy (DRS). This model system enables us to elucidate the mechanism of ion transport in charged polymer membranes. |
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N00.00051: Effect of water content and sulfonation level in a fluorine-free random copolymer on nanoscale morphology and proton transport Victoria S Lee, Max S Win, Amalie L Frischknecht, Karen I Winey Fluorine-free polymers are of interest for use as proton exchange membranes in fuel cells due to lower cost and greater membrane stability. The random copolymer under study consists of a linear polyethylene backbone with either a phenylsulfonic acid (p5PhSH) or phenyl (p5Ph) group pendant to every fifth carbon. We used atomistic molecular dynamics simulations to study the nanoscale morphology as a function of water content (λ = 3, 6, 9, and 12 waters per sulfonic acid) and sulfonation level (p5PhSH:p5Ph ratios of 50, 70, and 90%). The ion exchange capacity (IEC) of the copolymers ranges from 2.69-4.14 mmol/g. At higher λ and sulfonation values, systems exhibited percolated, bicontinuous domains of water and the hydrophobic polymer, as determined by visual analysis and cluster analysis. The water pore size distribution narrows as IEC and λ increase, indicating less tortuous channels. The water diffusion coefficient also increases with increasing IEC and λ. Fractal dimension df scales well with the diffusion coefficient because higher df indicates more isotropic water domains. When comparing results at 90% sulfonation to p5PhSH (95% sulfonation), the diffusion coefficient normalized by the bulk water diffusion coefficient is nearly identical, indicating similar behavior. |
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N00.00052: What is the impact of ion aggregation and counterion condensation on salt transport in ion exchange membranes? Nico Marioni, Akhila Rajesh, Zidan Zhang, Benny D Freeman, Venkatraghavan Ganesan Ion exchange membranes are widely used in water purification and energy storage applications to selectively and efficiently regulate salt transport. However, concerted motions of ions arising due to ion aggregation and counterion condensation are often neglected when interpreting salt transport. In this study, we apply the Onsager transport framework to atomistic molecular dynamics simulations to study the impact of such physics on salt transport properties in a model cation exchange membrane. Cations and anions, distinct cations, and distinct anions tend to move in the same direction due to the formation and resulting motion of ionic aggregates. Such motions, in general, increase the salt diffusion coefficient and decrease the conductivity relative to "ideal" values which envision the ions to move independently of each other. In contrast, condensation-induced slowdown inhibits the motion of ionic aggregates since the condensed counterions serve as a connection between aggregates and the immobile polymer matrix. Such effects decrease deviations of salt transport properties from the ideal assumption. |
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N00.00053: Impact of side chain comonomer PEGMA as blocking group in Ion exchnage membranes for CO2 reduction product crossover: Electrochemical Cell Application Antara Mazumder, Bryan S Beckingham CO2 reduction cells are one of the attractive techniques to cope with CO2 emission issue. A typical CO2 reduction cell consists of two cells separated by an ion exchange membrane (IEM). The major role of IEM is to prevent the transport of various CO2 reduction products (formate, acetate, methanol, and ethanol). Therefore, it is necessary to tailor the membranes to block the transport of these products. Previously, to suppress CO2 reduction product crossover we introduced a series of uncharged comonomers, acrylic acid (AA, n=0, where n is the number of PEG repeat units), hydroxyethyl methacrylate (HEMA, n=1), and poly(ethylene glycol) methacrylate (PEGMA, n=5), where we observed the crossover of carboxylates were significantly suppressed in PEGMA-containing films in co-diffusion. To further understand this, we prepared a series of PEGMA (n=9)- containing films and measured the permeabilities and solubilities of these films to carboxylates (formate and acetate) and alcohols (methanol and ethanol) in one- and two-component mixtures. In one-component permeation, we observed permeabilities to all solutes being increased with increasing PEGMA content (increased water volume fraction). However, emergent behavior was observed for the co-transport of carboxylates with alcohols. For instance, we observed the permeabilities to acetate in co-diffusion are decreased with increasing PEGMA content. This behavior motivates further investigation for rationally designing ion-exchange membranes. |
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N00.00054: Mixed binary alkali halide salt transport in PEO systems Aubrey Quigley, Everett S Zofchak, Nathaniel A Lynd, Benny D Freeman Salt permeability coefficients are important properties of membranes for industrial applications such as water purification and energy generation; however, there are few systematic studies probing the differences in permeability as a function of external solution composition. Understanding how ion transport is affected by the presence of other ions can help advance the design of membranes tailored with specific ion affinities. Here, we use a model cross-linked poly(ethylene glycol) diacrylate membrane to examine how permeability coefficients of binary alkali halide salt mixtures vary as a function of external salt mole fraction. We see that, at constant ionic strength, mixed salt permeability is largely governed by mixed salt partitioning. Furthermore, starting from the Nernst-Planck framework, we have derived a model for predicting permeability coefficients based off a thermodynamic partitioning model and the Mackie-Meares model for diffusion. This new model, with no adjustable parameters, shows great agreement in conditions with minimal ion-ether oxygen coordination (i.e., Na+, Cl-, and Br-), and shows slight overpredictions in cases with strong cation-oxygen binding (i.e., K+). |
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N00.00055: Tuning Interfacial Interactions for One-step Ordering of Block Copolymer Films with Tunable Pore Sizes for Wastewater Filtration Membranes Kshitij Sharma, Khadar B Shaik, Maninderjeet Singh, Chenhui Zhu, Mohammad K Hassan, Alamgir Karim Wastewater is now contaminated with oil, organic compounds, toxic metals, and a variety of complex impurities due to the rapid rise in oil and gas, petrochemical, pharmaceutical, and food processing industries. Polymeric membranes present an easy and energy-efficient solution for wastewater filtration. Versatile membranes that remove both particulate and oily matter from wastewater using multiple separation mechanisms are highly desirable. This work presents a methodology to rapidly order block copolymer thin films with well-defined through-thickness channels having minimal tortuosity. The technique involves casting BCP films from solution mixtures doped with block-selective plasticizing additives that segregate into one of the BCP domains. Owing to the selectivity and plasticization capability of the additive, its preferential solvation of BCP components in the solvent mixture, and its interaction with the substrate, the film is fully ordered with perpendicular domains on unmodified substrates. With careful selection of the casting environment, i.e., the concentration of the additive and the selective solvents, completely perpendicular domain morphologies with tunable domain sizes can be achieved during the casting process, potentially giving high fluxes and variable pore sizes. The thin BCP films form the active layers and are supported by commercial membranes like polyether sulfone for mechanical strength. They are treated to selectively crosslink one and etch the other block to open the pores which have size cutoffs for 90 percent solute rejection in the range of 40 nm to 80 nm. With monodisperse pore sizes and low tortuosity, they overcome the limitations of size segregation and flux. The perpendicular assembly is characterized by using atomic force microscopy and grazing incidence small angle x-ray scattering. At the same time, membrane performance is tested using a dead-end pressure cell to study flux, membrane stability, and separation efficiency for polymer solutions and oil/water suspensions. |
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N00.00056: Revealing selective analytes binding mechanism of PEGylated phospholipid CoPhMoRe by CG Molecular dynamics simulation Woojin Kim, Yullim Lee, Sooyeon Cho, YongJoo Kim Corona phase molecular recognition (CoPhMoRe) uses heteropolymer wrapping nanotube to recognize specific analytes for biosensing applications. Near-infrared fluorescent SWCNT (single walled carbon nanotube) where PEGylated phospholipid adsorbed can detect SARS-CoV-2 nucleocapsid and spike protein rapidly with label free. In this work, using CG (coarse grained) molecular dynamics simulation, PEGylated phospholipids with different hydrophobic tail, PEG length and different end groups with SWCNT were analyzed at various weight percent (wt%) to reveal which conditions provide a good binding space for analytes. According to the simulation results, hydrophobic tails have a very strong tendency to aggregate and the longer hydrophobic tail length, the stronger the clustering effect. As a result, the number of binding sites on the SWCNT surface increases. In addition, when the attraction to the SWCNT surface where lipid clustering occurred is enhanced and sufficient binding sites exist, more analytes can be adsorbed to the SWCNT surface. |
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N00.00057: Probing the Impact of Chain Architecture on Segmental Dynamics in Semi-Crystalline Poly(oligocyclobutane) Shawn M Maguire, Stavros Drakopoulos, Cherish Nie, Richard A Register, Paul J Chirik, Rodney D Priestley, Emily C Davidson Recently, a new family of alkene-spaced semi-crystalline poly(oligocyclobutyl) (pDVOCB) polymers derived from butadiene has been synthesized. These unique polymer microstructures have demonstrated promise as chemical recyclable polymers with excellent retention of their tunable, thermomechanical properties. However, due to the high crystallinity innate to this microstructure, information regarding their segmental dynamics has been difficult to detect via traditional calorimetry as the heat capacity increment is small due to the small amorphous fraction. In this work, the molecular dynamics of a series of pDVOCB polymers are studied via experimental relaxation dynamics techniques. Leveraging the improved sensitivity of these techniques to chain relaxations, insights into the effects of varying monomer architecture, tacticity, and molecular weight are obtained. Further, secondary relaxation processes are found to occur at lower temperatures, related to the local movements of cyclobutyl units. This improved understanding of molecular motions in pDVOCB, as well as the governing factors influencing them, provides insights into structure-property relationships important for the design, processing, and applications of these chemically recyclable polyolefins. |
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N00.00058: Core-Modified DPD Simulations of Helical Polymers on Spherical Nanoparticle Surfaces Michael A Hore, Ankit Saha Polymer helices exhibit a precise arrangement of monomers and functional groups along an axis, which leads to unique chemical and physical properties, with particular uses for biological and medical applications. Mixing polymers and nanoparticles (NPs) to make nanocomposites can further enhance or augment the physical properties of materials. However, to achieve improved properties from the nanoparticle component, the spatial dispersion of NPs needs to be fine-tuned. Grafting polymers to the NP surface is one method to control dispersion. The combination of nanoparticle surface curvature and the spatial confinement between adjacent chains can alter the conformation of the grafted polymers and also affect the quality of the NP dispersion. Here, we study the structure and dynamics of helical polymers grafted to a spherical NP surface using a combination of core-modified DPD simulations and proper orthogonal decomposition (POD) of the monomer motions to examine their relaxation modes. Although the relaxation modes are not affected by the helical structure of the chains, we find quantitative differences in the structure and relaxation times of the helical brush as compared to traditional polymer-grafted NPs. |
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N00.00059: Self-diffusion of Linear and Star Polyacids in Layer-by-Layer Films: Impact of the Polycation Molecular Weight Parin Purvin Shah, Aliaksei Aliakseyeu, Jordan Brito, Svetlana A Sukhishvili We explore the effect of molecular weight of a polycation – poly(diallyldimethylammonium chloride) PDADMAC (35 kDa, 70 kDa, and 325kDa) - on the salt-triggered lateral diffusion of linear and star poly(methacrylic acid)s (L-PMAA and s-PMAA, respectively) of matched molecular weight (60 kDa) in layer-by-layer (LbL) films. Both L-PMAA and s-PMAA deposited exponentially with low molecular weight PDADMAC at pH 5, but formed thinner, linearly growing films with higher molecular weight PDADMAC, suggesting slower polymer mobility. Exposure of the assembled films to NaCl solutions revealed higher stability of films containing linear polymers compared to star-containing films, and increased stability of films constructed with high molecular weight of PDADMAC. FTIR studies showed that an increase of Mw of PDADAMC led to lower ionization of both linear and star PMAA in the films suggesting a significant dependence of density of ionic pairing on molecular weight. Fluorescence recovery after photobleaching (FRAP) technique was used to measure lateral diffusion of Alexa-488 labeled polyacids. The diffusion coefficients (DII) of the assembled polyacids were lower for films constructed with higher-molecular-weight PDADMAC, and films of linear and star polymers exhibiting different scaling exponents for such as dependence. This work provides an insight into mobility of assembled linear and star polyelectrolytes and their dependence on the local structure of LbL films determined by a binding partner. |
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N00.00060: Structural Dynamics Evolution of EVOH during Polymer Upcycling Reaction by Ex-Situ Electrochemical Impedance Spectroscopy Chien-Hua Tu, Eli J Fastow, Anne Radzanowski, Bryan Coughlin, Karen I Winey Ethylene vinyl alcohol copolymers (EVOH) have several applications including food packaging given its exceptional vapor and oil barrier performance. While EVOH traditionally has a branched architecture, we study a linear EVOH synthesized by hydroboration/oxidation of alkenes in polycyclooctene . This new synthetic route produces EVOH with partially unsaturated or fully saturated backbones and a range of hydroxyl functionality. |
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N00.00061: Implicit-solvent coarse-grained simulations of linear-dendritic block copolymer micelles Mariano E Brito, Sofia Mikhtaniuk, Igor M Neelov, Oleg Borisov, Christian L Holm A variety of nanoassemblies can be conveniently achieved by fine-tuning the strength of the hydrophobic interactions of block copolymers in selective solvents, giving rise to assemblies with various interesting topologies. In particular, block copolymer micelles have attracted great attention in the area of drug delivery and imaging in biomedicine due to their easy-to-tune properties and straightforward large-scale production. In the present work, we have investigated the micellization process of linear–dendritic block copolymers in order to elucidate the effect of branching on the micellar properties. We focus on block copolymers formed by linear hydrophobic blocks attached to either dendritic neutral or charged hydrophilic blocks. We have implemented a simple protocol for determining the equilibrium micellar size, which permits the study of linear–dendritic block copolymers in a wide range of block morphologies in an efficient and parallelizable manner. We have explored the impact of different topological and charge properties of the hydrophilic blocks on the equilibrium micellar properties and compared them to predictions from self-consistent field theory and scaling theory. We have found that, at higher degrees of branching in the corona and for short polymer chains, excluded volume interactions strongly influence the micellar aggregation as well as their effective charge. |
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N00.00062: Optimizing the Synthesis of High Molecular Weight Thermoresponsive Triblock Copolymers for Processing Scalability Clarissa Huisman, Jason D Linn, Soumi Das, Michelle A Calabrese Stimuli-responsive block copolymers are used in a variety of applications including printable electronics, thermoresponsive spray coatings, and drug delivery systems. These polymers are especially favorable in applications due to their tunable properties, versatility, and potential scalability. Polymer architecture has a crucial role in responsiveness, and reversible addition-fragmentation chain transfer (RAFT) polymerization can be used to achieve well-controlled polymers. In this project, RAFT is used to synthesize low dispersity poly(N-isopropylacrylamide-b-dimethylacrylamide) (P(NIPAM-b-DMA)) triblock copolymers. Polymerization was carried out using two RAFT chain transfer agents, 2-(1-carboxy-1-methylethylsulfanylthiocarbonylsulfanyl)-2-methylpropionic acid (CMP) and 2-(dodecylthiocarbonothioylthio)-2-methylpropanoic acid (bis-DDMAT). CMP contains end carboxyl groups, while bis-DDMAT contains end dodecyl carbon chains creating different resulting triblock structures, which should lead to different behaviors in solution. While previous experiments utilizing these triblocks were limited to lower molecular weight polymers, larger molecular weight polymers tend to have higher tensile strength and better longevity in applications. Therefore, we are interested in raising the molecular weight of these polymers to study how this affects structure and processability. Following successful synthesis, cloud-point testing was performed to study optical properties of the polymers as a function of temperature. This work connecting polymer architecture to solution processability will be beneficial to increase the scalability of these stimuli-responsive polymers. |
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N00.00063: Magnetic Field Induced Ordering Of Block Copolymers Milena Mesfun, Arit Das, Grace Kresge, Michelle A Calabrese Poloxamers are amphiphilic ABA type triblock co-polymers that act like a surfactant in water, creating a micelle with a “B” type polypropylene oxide core and “A” type polyethylene oxide coronas. They are widely applicable as hydrogels, which are notably utilized in biocatalysis, drug delivery, and drug stability. In this project, we probed an atypical response of disordered poloxamer solution to ordered gel transition in response to magnetic fields. The behavior of a poloxamer solution in presence of an applied magnetic field (B = 0.5T) was investigated using magnetorheology, where the rheological characteristics of the samples were studied while exposed to an in situ magnetic field. Specifically, the time required by the poloxamers to transition from their disordered to gel state under magnetization, referred to as critical time, was tracked as a function of block ratio and molecular weight. The gels were characterized using small-angle x-ray scattering (SAXS), which revealed their structural information. The critical time decreased exponentially and the modulus remained relatively consistent when increasing the molecular weight of the poloxamer. These results demonstrate the tunability of magnetically-induced poloxamer gels for wide-ranging applications. |
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N00.00064: Mechanism of Plasticization and Antiplasticization in Chitosan-Based Systems Baris Eser Ugur, Michael A Webb Plasticization is often utilized to modify the thermomechanical properties of polymeric materials for various applications. While the effects of plasticizers have been well characterized for a wide array of polymer-additive combinations, the molecular mechanism of plasticization is not fully understood. We employ molecular dynamics simulations to characterize the mechanism of plasticization and antiplasticization in chitosan-based systems with a focus on nanoscale additive-polymer interactions and their effects on the glass transition temperature and elastic properties of the material at various temperatures. We evaluate the validity of previously proposed theories on the plasticization phenomena, and highlight specific chemical moieties that govern the plasticization and antiplaticization mechanism. Furthermore, we investigate the evolution of nano- and macroscale properties at the antiplasticization to plasticization crossover concentration to establish a structure-property relationship. This study aims to help understand the effect of additives in polymer properties and allow more informed design of plasticized systems for applications including pharmaceutics, packaging and agriculture. |
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N00.00065: Mechanics of 3D Printed Microbial Hydrogel Composites Samson O Adelani, Nicole Garza, Morgan B Riffe, Jason A Burdick, Konane Bay The majority of 3D-printed engineered living materials are printed on flat surfaces limiting the complexity and size of the materials. Additionally, the interplay between microbial cell density and hydrogel matrix stiffness has been shown to impact the final mechanical properties of 3D-printed microbial hydrogel composites. However, since these inks of materials are typically extremely soft, they require crosslinking as they are 3D printed. Therefore, the final mechanical properties of these materials are fixed in the 3D printing process. We will overcome these challenges, by utilizing a 3D support media that fixes the ink into place allowing for the cells to grow before crosslinking. Here, we 3D print photocrosslinkable methacrylated hyaluronic acid and Escherichia coli into a 3D support media swollen with liquid growth media. We show how crosslinking after incubating the 3D printed impacts the final cell density and stiffness of the microbial hydrogel composites. Our results thus provide fundamental insights into how the growth of cells in confined environments can affect the mechanics of 3D-printed microbial hydrogel composites. |
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N00.00066: Modeling microwave-induced heating of 3D-Printed Structures of Polypropylene filled with SiC Whiskers Arefin M. Anik, Erik L Antonio, Igor Luzinov, Olga Kuksenok One of the widely used methods of 3D printing of polymers is fused deposition modeling (FDM) or fused filament fabrication(FFF), which requires a thermoplastic filament to be directed toward a heating block and then deposited layer-by-layer to produce a finished part. Polypropylene(PP) is one of the widely used polymers due to its properties, processability, and low cost. Silicon carbide (SiC) whiskers dispersed within PP matrix absorb microwave radiation and generate heat. To model microwave-induced heating of PP-SiC composites, we solved a heat transfer equation within the cubic sample coupled with the electromagnetic wave equation within the entire microwave oven. We use COMSOL Multiphysics@ software to integrate this system of equations. The composite properties were assumed to be uniform on the length scale of interest. We varied the volume fraction of the SiC whiskers (from 0.3 vol % to 3.0 vol %) and calculated the temperature within the samples during the microwave heating. Our modeling results approximately captured the extent of heating observed in our experiments. Our concurrent experiments also showed (ELS Antonio et al, ACS Appl. Mat & Interf 15, 40042, 2003) that microwave heating of the 3D-printed sample significantly improves its mechanical properties. |
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N00.00067: Continuous Spun Fibers via Centrifugal Force Spinning Louie Edano, Cheryl L Slykas, Vihar Trada, Carina Martinez, Naveen Reddy, Vivek Sharma Centrifugal Force Spinning (CFS) provides an alternative fiber spinning method from other well-developed fiber spinning methods, and allows for quick and efficient manufacture of continuously spun fibers. In this contribution, a list of ideal polymer solution properties such as polymer entanglements, extensional relaxation time, and evaporation rate is compiled through torsional rheometry, Dripping-onto-Substrate (DoS) protocols, and thermogravimetric analysis (TGA). These properties are paired together with fiber spinning process parameters to provide an optimized processability map, predicting fiber formation and morphology. The resulting fiber morphologies are observed through SEM and the fiber mat mechanical properties are characterized. |
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N00.00068: Tuning Polymorphism of Poly(vinylidene fluoride) Thin Films via Capillary Pen 3D Printing Jiaen Wu, Shawn M Maguire, David Bershadsky, Emily C Davidson The β-phase crystal structure of poly(vinylidene fluoride) (PVDF) exhibits superior ferroelectric properties relative to other PVDF polymorphs. Therefore, promotion of this phase via processing is an ongoing pursuit in the field of energy storage, especially for polymer-based dielectric capacitors. However, the β-phase is not thermodynamically favored, requiring implementation of non-equilibrium techniques including stretching, electric field poling, ultrafast quenches from the melt, and filler addition. Here, we demonstrate a method to tune β-phase crystal content in PVDF thin films via capillary pen 3D printing. This allows for fabrication of thin-films of highly controllable thickness and geometry through simple modification of print conditions. By balancing flows within the PVDF solution during printing coupled with solvent evaporation kinetics and controlled substrate temperature, β-phase crystal content can be tuned in stable films of 80-500 nm thickness. Thus, capillary pen 3D printing is a simple, one-step method that allows for precise control over polymer microstructure and demonstrates promise as a technique to prepare thin-films used in polymer-based dielectric materials with increased energy capacitance. |
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N00.00069: Evolution of Polystyrene Adhesion on a Si Substrate Coupled with Interfacial Structural Relaxation REIKI ETO, Hidenobu Taneda, Yuma Morimitsu, Keiji Tanaka Adhesion using polymers to assemble various materials has been attracting attention as an alternative to mechanical bonding. This is because polymer adhesion promotes lighter weight and higher toughness in structural materials, such as in mobility applications. Polymer adhesion is expected to depend on van der Waals forces and is considered to develop at the point of contact between the polymer and the adherend. However, it is also known empirically that adhesive force increases over time after contact. This is expected to be related to the structural relaxation of polymers, however, it is still open. In this study, with the aim of elucidating the polymer adhesion mechanism at the molecular level, we systematically changed the condition of the annealing process for polystyrene (PS) thin films on the adherend, Si substrates, and examined the effects of heat treatment on the adhesion properties. The adhesion strength drastically increased after thermal annealing at 50 K above the glass transition temperature for 1 h. In addition, the adhesive strength gently increased as the annealing time. This indicates that the adhesion strength depended on not only van der Waals forces but also the conformation of polymer chains at the interface. |
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N00.00070: In-Situ Real-time AFM Observation of Folded-Chain Crystallization of Single Isolated Isotactic Poly(methyl methacrylate) Chains in a Langmuir-Blodgett Monolayer at the Molecular Level Jiro Kumaki, Yusaku Takahashi The crystallization process of a single isolated polymer chain into a folded-chain crystal (FCC) was clearly visualized at the stem level in situ and in real time by atomic force microscopy (AFM). The sample was a single Langmuir monolayer deposited on mica, in which isotactic poly(methyl methacrylate) (it-PMMA) was solubilized as isolated chains in an it-oligo(MMA) monolayer, the molecular weight of which was too small to crystallize.. The crystallization of an isolated it-PMMA chain into a FCC composed of a double-stranded helix of the single chain occurred under high humidity and was followed by AFM. The nucleation occurred at any point of the chain and the crystal grew by winding the residual part of the amorphous chain. Under the humidity condition at which the nucleation occurred frequently, multiple crystals were formed in a single chain to form a necklace crystal. Further, the growth of a crystal formed at the end of an amorphous chain was observed at the stem level. Unexpectedly, the crystal grew not only on the side where the amorphous chain was attached but also significantly on the opposite side where no amorphous chain was attached, clearly indicating that the chains significantly slipped inside the folded double-stranded-helix crystal and crystallized on the opposite side. The crystallization behavior of a single isolated chain provides new insight in understanding the polymer crystallization process. |
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N00.00071: On slip predictability for sheared granular systems Lou Kondic, Philip Bretz, Miro Kramar We consider a sheared granular system experiencing intermittent dynamics of stick-slip type via discrete element simulations. The considered setup consists of a two-dimensional system of soft frictional particles between solid walls, one of which is exposed to a shearing force. The slip events are detected using stochastic state space models applied to various measures describing the system. We show that the measures describing the forces between the particles provide earlier detection of an upcoming slip event than the measures based solely on the wall movement. We find that a typical slip event starts with a local change in the force network. For the changes that become global, we find a sharp critical value for their size. If the size of a global change exceeds the critical value, it triggers a slip event; if it does not, a much weaker micro-slip follows. Quantification of the changes in the force network is made possible by formulating clear and precise measures describing their static and dynamic properties. |
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N00.00072: Unveiling the Role of Physicochemical Bonds on the Mechanical Behavior of Colloidal Gels Elnaz Nikoumanesh, Ryan Poling-Skutvik Soft materials are characterized by their intricate interplay of structure, dynamics, and rheological properties. This complexity makes it challenging to accurately predict their response to shear stress. Here, we investigate how the nature of colloidal bonds – entropic repulsion, physical entanglements, electrostatic attractions, and covalent bonds – affect the mechanical characteristics of gels. Our research aims to enhance our ability to engineer gels and colloidal suspensions with tailored responses and advanced functionalities by exploring the fundamental physics governing these responses. We selected diverse models that encompass a broad spectrum of materials, each possessing unique chemical bonds within their microstructure, such as cellulose nanocrystals modified with salt, bentonite, Carbopol, and cellulose nanofibers. We investigate the critical role played by these structural bonds and their response to linear and nonlinear deformations. Specifically, we apply our novel rheological approach – serial creep divergence (SCD) – to accurately determine the yield transition and critical stress and to reveal the physics and origin of yielding. This comprehensive approach allows for a detailed comparison of how these materials respond to shear stress, ultimately advancing our understanding of the intricate interplay between chemical bonding and material behavior within soft, amorphous materials. |
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N00.00073: Dynamic Heterogeneity in Plasticized Polystyrene Thin Films Jaladhar Mahato, Han Yang, Alec Robert Meacham, Laura Kaufman Polymer dynamics near the glass transition temperature (Tg) is complex, and a complete molecular scale theory for the glass transition is lacking. Relaxation timescales that characterize polymer dynamics near Tg display highly non-exponential behavior and span several orders of magnitude on approaching Tg. Rotational dynamics of individual fluorescent probes provide insight into host nanoscale environments, thereby reporting local dynamics typically obscured in ensemble measurements. Modulation of a polymer matrix network’s rigidity by swelling with good solvents is an understudied route to accessing dynamics in the glassy regime, and such experiments can shed light on plasticization processes. We perform controlled swelling of polystyrene with toluene, monitored via a quartz crystal microbalance (QCM), to target effective temperatures near Tg as monitored by the average rotational correlation time of perylene diimide probe molecules. Characterizing the distribution of rotational correlation time and degree of non-exponentiality of individual probe molecule relaxation reveals clear differences in the degree and temporal persistence of heterogeneity in solvent-swollen compared to temperature-controlled polystyrene in the rubbery regime. |
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N00.00074: Characterizing Rotational Dynamics in Glassy Systems from Single Molecule Intensity Fluctuations Alec R Meacham, Jaladhar Mahato, Han Yang, Laura Kaufman The dynamic heterogeneity exhibited by molecular rotations in glassy systems has long been characterized at the single molecule (SM) level by extracting timescales from linear dichroism (LD) collected via orthogonally polarized, wide-field fluorescence imaging. However, due to photons lost when collecting fluorescence images in this manner, localization precision is diminished relative to single channel collection. This makes examinations of dynamic heterogeneity as it manifests in translation measurements and the associated phenomenon of rotational-translational decoupling challenging to characterize as such measurements require high localization precision. Here, a method for extracting rotational dynamics of glassy systems at the SM level from intensity fluctuations of fluorescent probe molecules excited with circularly polarized light and collected in a single channel configuration is presented. Rotational dynamic timescales and degree of heterogeneity extracted from the LD and intensity approaches show good agreement, and the intensity-based approach is demonstrated to be robust across optical configurations, probe molecules, and in both polymeric and small molecule glass formers. |
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N00.00075: Probing the Viscoelastic Properties of Stable Glass Surfaces Weiduo Wang, Brandon Mcclimon, Peng Luo, Kritika jha, Robert W Carpick, Zahra Fakhraai Nanoscale glass films are widely used in coating and display industries. However, their properties can deviate greatly from those of bulk glasses, which has been attributed to the existence of a liquid-like surface. Experimental and simulation work show a complex dependence of the surface relaxation time and elasticity on temperature. Here we use Atomic Force Microscopy (AFM) based nanoscale dynamic mechanical analysis (nDMA) to study the mechanical properties of the surfaces of various molecular glass systems. These films are produced either through physical vapor deposition to make stable glasses (SG), or through liquid cooling to produce ordinary glasses (OG). With tuning the applied force and contact area, we measure the local mechanical properties profile at various depths from the surface. The surface of all glass films (Both SG and OG) shows strong viscoelastic behavior and become liquid-like at frequencies below several Hertz, well below their glass transition temperature (Tg), corresponding to a much faster relaxation times compared to the bulk. We also observed a strong gradient of the relaxation within the surface, indicating dynamical anisotropy of the surface layer. However, temperature-dependent measurements indicate that the change in surface Tg may highly depend on the choice of the molecule. These results provide insight into the gradients of surface elasticity with high depth precision. |
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N00.00076: Bioorthogonal synthesis of supramolecular peptide polymers Hanyuan Gao, Tianren Zhang, Matthew G Langenstein, Weiran Xie, Jeffery G Saven, Shi Bai, Darrin J Pochan, Joseph M Fox, Xinqiao Jia High molecular weight supramolecular peptide polymers with tunable composition, chain flexibility and dynamic properties represent the next-generation advanced materials that overcome the limitations of covalently constructed synthetic polymers. Herein, computationally designed peptides capable of forming antiparallel, coiled-coil, α-helical bundles were utilized as the monomers (bundlemer) to synthesize high molecular weight protein-like supramolecular assemblies. Solution phase step-growth polymerization was performed in aqueous media employing an efficient, rapid and bioorthogonal cycloaddition reaction between s-tetrazines (Tz) and trans-cyclooctenes (TCO). The resultant polymers were characterized physically to determine the intrinsic viscosity, diffusion coefficient and hydrodynamic radius. The apparent polymer molecular weight was estimated to be 100-3000 kDa. Measurements by transmission electron microscope and small angle X-ray scattering indicate the formation of long, semiflexible/flexible rods with a Kuhn length of 6-7 nm. When the polymerization concentration increased, physical gels with defined viscoelastic properties were obtained via intermolecular entanglements. Hydrogels prepared at a higher bundlemer concentration were found stiffer than those obtained at a lower concentration. Overall, the combination of novel coiled-coil bundlemer with bioorthogonal Tz-TCO ligation led to the establishment of protein-like supramolecular polymers. |
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N00.00077: Electrostatic Driven Self-Assembly of Polyoxometalate Macroions in Divalent Salt Solution Ali Hatami, Yingxi Elaine Zhu, Adithya Rathinasabapathy Supramolecular assembly of subnanometer-size macroions, including peptides, proteins, and lipids, in aqueous solutions has gained much interest for their wide potential applications ranging from nanomedicine to energy storage. The electrostatic attraction and self-assembly of multivalent macroions remain inadequately understood, where Debye−Huckel theory for small ions or the DLVO theory for charged colloids become inapplicable. Recently, we have found that inorganic polytungstate (Li6H2W12O40, {W12}) polyoxometalate (POM), which is about 0.8 nm in diameter and bears 8 negative charges upon fully dissolved in water, can spontaneously assemble into well-organized structures of 5-10 mm in narrow size distribution in divalent salt solution. It is in sharp contrast to the thermodynamically stable {W12} aqueous solution added with monovalent salt such as LiCl. As increasing the concentrations of {W12} and CaCl2, We have observed the transformation of supramolecular assemblies into various shapes, including rods, dumbbell shapes, and spheres, using both SEM and confocal microscopy. Such multivalent counterion-mediated electrostatic control of macroion assembly could be general and extended to other POMs and even hybrid inorganic-organic macroion mixtures, opening new approaches to develop nanoscale functional materials. |
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N00.00078: Bound and Bulk Methanol Relaxation of Poly(N-isopropylacrylamide) in a Water-Methanol Mixture Eric Rende, Bart-Jan Niebuur, Wiebke Lohstroh, Christine Papadakis, Alfons Schulte The competition between water and methanol for binding to a thermoresponsive polymer constitutes a fundamental aspect of the co-nonsolvency effect, where the addition of a cosolvent such as methanol to an aqueous polymer solution may lead to a strong reduction of the cloud point and reentrant behavior. The dynamics of water bound to the polymer has been thoroughly studied, however the association of a methanol cosolvent with the polymer chain has been far less characterized. We present an analysis of quasi-elastic neutron scattering (QENS) measurements conducted on a 25 wt% poly(N-isopropylacrylamide) (PNIPAM) solution in water/methanol solvent across the demixing transition. By measuring the signal in solvents differing only by their isotopic composition, the contribution of methanol relative to that of water, i.e. their mutual dynamics, was determined. Analysis of QENS spectra of PNIPAM in a D2O-methanol mixture over a wide frequency range reveals an additional contribution at lower frequencies that may be attributed to methanol associated with the polymer chain, in addition to the bulk diffusion peak. |
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N00.00079: Block Polyelectrolytes Scaffolds Enable 3D Printing of Gelatin Inks at Physiological Temperatures Fahed Albreiki, Tobias Göckler, Defu Li, Alisa Grimm, Felix Mecklenburg, Juan Manuel Urueña, Samanvaya Srivastava, Ute Schepers Rapid prototyping of computer-aided 3D printing of cells is expected to open great avenues in the field of tissue engineering. However, efforts to meet the growing need for biomaterials that act as 'bioinks' for 3D bioprinting are hindered due to the poor mechanical properties of most bioinks. In this contribution, we demonstrate the utility of block polyelectrolyte (bPE) additives to enhance the viscosity and resolve longstanding challenges with three-dimensional printability of extrusion-based biopolymer inks. The addition of oppositely charged bPEs into solutions of photocurable gelatin methacryloyl (GelMA) results in complexation-driven self-assembly of the bPEs, leading to GelMA/bPE inks that are printable at physiological temperatures, representing stark improvements over GelMA inks that suffer from low viscosity at 37 °C leading to low printability and poor structural stability. Hierarchical microstructures of the oppositely charged bPE self-assemblies (either jammed micelles or three-dimensional networks), confirmed by small angle X-ray scattering, is attributed to the enhancements in the shear strength and printability of the GelMA/bPE inks. Varying bPE concentrations enabled facile tuning of the rheological properties to meet the criteria for pre- and post-extrusion flow characteristics for 3D printing. Furthermore, bPE self-assemblies enhance the shear strength of photocrosslinked GelMA hydrogels – photocrosslinked GelMA/bPE hydrogels exhibit higher shear strength than GelMA hydrogels. Moreover, we show the printability assessment of GelMA/bPE inks which indicate excellent two- and three-dimensional printing performance. |
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N00.00080: Rheology of Microstructurally Rearranged Polyelectrolyte Complex Hydrogels Holly Senebandith, Fahed Albreiki, Samanvaya Srivastava In this poster, we present rheological data related to the swelling and dehydration response of polyelectrolyte complex (PEC) hydrogels. PEC hydrogels are self-assembled from ABA + CBC triblock polyelectrolytes (PEs) due to electrostatic attraction and increased entropy from counterion and water molecule release. These hydrogels experience a myriad of microstructures that are influenced by both internal (charged-block length, PE concentration) and external (salt, pH) parameters. In this study, we establish PEC hydrogels as equilibrium structures through a series of controlled swelling and dehydration-rehydration experiments by probing the microstructural rearrangements with small-angle scattering experiments. Furthermore, we investigate the effect of these rearrangements on the shear properties of the PEC hydrogels by performing rheology measurements. We present our findings on the moduli of PEC hydrogels that were diluted to lower PE concentrations and the moduli of PEC hydrogels that were de- and then rehydrated to various PE concentrations by comparing them to the moduli of their pristine counterparts at the same PE concentrations. Additionally, we present our results on the moduli of mixtures of PEC hydrogels with initially distinct microstructures. We show that PEC microstructure and the resulting rheological properties can be modulated through dilution, dehydration, and mixing of PEC hydrogels demonstrating in situ tunability. |
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N00.00081: Linking bed forces to granular rheology in geophysical flows using DEM-CFD P.J. H Zrelak, Eric Breard, Josef Dufek Basal forces exerted by geophysical granular flows are responsible for the generation of observable seismic signals. These signals may provide a safe means for remotely analyzing internal dynamics in real-time. To realize the benefit of seismic measurements, basal granular forces must be linked to macroscopic flow dynamics across a range of flow conditions. We perform discrete element simulations of dry and submerged granular flows under plane-shear and inclined flow configurations, relating bulk rheology to basal forces. We find that the variance in basal forcing scales with inertial number (I). We differentiate four flow regimes tracked by this scaling: (1) unsteady particle rearrangement when I < 10-3, where basal forces are dominated by low frequencies and granular temperature is anisotropic in the vertical direction; (2) an intermediate regime when 10-3 < I < 10-2, where granular temperature is isotropic, and basal force fluctuation scaling with I strengthens; (3) a transitional regime when 10-2 < I < 10-1, where increases in basal force fluctuations with I is interupted as the granular bed dilates, partially erasing the contact network and configurational memory; and (4) a collisional regime when I > 10-1, granular temperature becomes anisotropic in the stream-wise direction, and the signal becomes white noise-like up to a cutoff frequency that is dependent on particle scale parameters. These data show that information about complex granular flow rheology maybe encoded in basal interactions. |
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N00.00082: Abstract Withdrawn
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N00.00083: Characterization of Polymer-Grafted Nanorods by Depolarized Dynamic Light Scattering with Genetic Algorithm Optimization Michael A Hore, Nehal Nupnar, Kiril A Streletzky, Geofrey M Nyabere Gold nanorods (AuNRs) have garnered significant attention due to their uniform dimensions and unique optical properties, making them promising candidates for various applications, including drug delivery, imaging, and sensing. For many of these applications, polymers are typically grafted to the AuNR surface to tune solubility, dispersion, immune response, and other important properties. However, characterizing polymer-grafted nanorods with electron microscopy can be difficult and time-consuming, while appropriate analytical form factors for neutron scattering analysis have yet to be identified. Here, we present a novel approach that combines depolarized dynamic light scattering (DDLS) with a genetic algorithm (GA) optimization method that uses the experimentally obtained relaxation rates to quickly determine the optimal dimensions of AuNRs, while also quantifying the deviation from theoretical values. Our work demonstrates that this approach is a fast, cost-effective, and versatile method for characterizing polymer-grafted nanorods in solution, thus addressing a critical need in nanomaterial characterization. Our study of polymer-grafted AuNRs not only aids in understanding polymer behavior but also opens up new possibilities for designing advanced nanocomposite materials. |
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N00.00084: Interfacial nanoparticle layers: Nanorheology and phase separation monitored by scanning electron microscopy. Katelynn O'Donnell, Anthony Raykh, Alexander E Ribbe, Thomas P Russell, David Hoagland Recent advances in electron microscopy enable single-particle monitoring of dense, nanoparticle-laden fluid interfaces. Applying scanning electron microscopy to these interfaces, real-time, in situ nanorheology was performed to understand connections between nanoparticle properties, nanoscale packing and dynamics, and bulk interfacial properties. Such systems display unique behaviors due to the finite ratio of stabilizing ligand size to particle size, affecting the softness of interparticle interactions. To conduct nanorheology experiments in the microscope, new liquid devices and new nanoparticle systems were devised to facilitate quantitative visualization while macroscopic properties (e.g., surface pressure, moduli) were measured. Modification of ligands (e.g., chemistry, length) allowed the tuning of both wetting dynamics and two-dimensional interparticle enthaplic and entropic interactions. When different components (e.g., geometically dissimilar nanoparticles, similar nanoparticles with dissilimar ligands, nanoparticles and polymers) were mixed, two-dimensional phase separation was observed at the nanoscale. |
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N00.00085: High-throughput fabrication of geometrically complex nanoenvironments for single-molecule fluorescence microscopy Louis Wang, Danielle J Mai Nanoenvironments with complex geometries mimic biological interfaces such as the synovial joint, making them valuable tools for investigating single-molecule behavior in biomimetic systems. Current environments that replicate both the interfacial gap (0.01 μm) and roughness (10 μm characteristic wavelength) of the native synovial joint are typically fabricated using focused ion beam (FIB) milling. However, FIB requires serial fabrication of nanoenvironments, making it unfavorable for high-throughput fabrication. In this study, we fabricate multiple 3D nanoenvironments simultaneously by reactive ion etching (RIE) of optically transparent borosilicate glass substrates. Here, we use grayscale photolithography to define 3D photoresist patterns and RIE to transfer photoresist patterns to borosilicate substrates. We characterize etched surface roughnesses using atomic force microscopy and validate etched geometries using laser scanning confocal microscopy. We demonstrate that the range of nanofabricated feature depths and pitches is sufficient to create biomimetic synovial joint environments. These environments will be used to characterize the dynamic behavior of biopolymers using single-molecule fluorescence microscopy. |
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N00.00086: A Photochemical Approach to Realizing an On-Demand Switchable Polymer between a Thermoset and a Vitrimer GYEONGHWAN CHOI, Chae Bin Kim The inability of thermosets to be melt-processed significantly limits their recycling potential because the simplest and most economical way to recycle polymers is to repair or remelt them into new items. A new class of polymer, known as a vitrimer, which features exchangeable covalent bonds, has garnered significant attention as a recyclable and repairable alternative to thermosets. However, the bond exchange chemistries in conventional vitrimers are thermally activated, suggesting that a limited temperature range exists for vitrimers to function as strong thermosets. In this presentation, we propose a sequential photochemical approach to convert a thermoset into a vitrimer and then back into a thermoset on demand. This can be achieved by incorporating a set of latent, heat-stable photo-active catalysts into a model epoxy thermoset. Two photo exposures with different irradiating wavelengths were applied. The first photo exposure releases a catalyst, activating the bond exchange, while the subsequent photo exposure deactivates the catalyst. This approach allows for an on-demand switchable polymer that can alternate between a thermoset and a vitrimer. |
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N00.00087: Enabling Circularity and Upcycling of Post-Consumer-Use Flexible Polyurethane Foam Divya Iyer, Mohammad Galadari, Fernaldy Wirawan, Holly Senebandith, Lucas Willey, Rong Feung Peter Goh, Patrick Getty, Michael Gallagher, Dante Simonetti, Gaurav Sant, Samanvaya Srivastava Of the 15 million metric tons of polyurethane (PU) waste generated annually in the US, flexible PU foam accounts for ~30%. Mattresses comprise 40% of the PU flexible foam market; nearly 50,000 mattresses are discarded daily in the US and each year, 20 million mattresses end up in landfills. Mattresses comprise flexible PU foam layers (memory foam, support foam) with varying chemical compositions (extent of cross-linking or foaming). An absence of comprehensive and easy strategies to classify these layers limits the thorough recycling and appropriate disposal of post-consumer flexible PU foam. To address this challenge, an inexpensive and field-employable strategy correlating observable physical properties to the chemical composition and thermo-mechanical properties of these foams will be shown. This will aid industrial recycling strategies tailored to post-consumer-use flexible PU foam layers. |
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N00.00088: Non-local Shortest Paths: Microstructural Evolution controls Macroscopic Response for Dynamic Polymer Networks Shaswat Mohanty, Yikai Yin, Christopher B Cooper, Zhenan Bao, Wei Cai Highly stretchable and self-healable supramolecular elastomers are promising materials for future soft electronics, biomimetic systems, and smart textiles, to name a few, due to their dynamic cross-linking bonds. The dynamic or reversible nature of the cross-links gives rise to interesting macroscopic responses in these materials such as self-healing and rapid stress-relaxation. However, the relationship between bond activity and macroscopic mechanical response, and the self-healing properties of these dynamic polymer networks (DPNs) remains poorly understood. |
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N00.00089: Direct Observation of Covalent Adaptable Network Rearrangement Using Single-Particle Tracking Christopher Rademacher, Muzhou Wang, Julia A Kalow Covalent adaptable networks (CANs) have received significant attention recently because of their potential to replace conventional thermosets with recyclable materials. Current research has been limited to investigations into different chemistries and functional groups that enable structural rearrangement. This leaves a gap in understanding the nanoscale dynamics that govern this rearrangement. In this work, we synthesized CANs from poly(n-butyl acrylate-s-hydroxyethyl acrylate) (PnBA-HEA) and boric acid. With this chemistry, we will directly visualize the self-diffusion of P(nBA-HEA) chains before and after crosslinking. By tuning the molecular weight between crosslinks as well as the bond strength of the crosslinks, a wide range of diffusive behavior can be accessed. Additionally, the self-healing of adaptable networks can be visualized by dye-labeling one half of an interface and observing the evolution of the interface. Results from this study will be broadly applicable to CANs and can inform how to better design and reprocess them. |
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N00.00090: Poly(n-hexyl methacrylate) Covalent Adaptable Networks (CANs) Made by Reactive Processing to Link Alkyl Side Chains with Dynamic Covalent Bonds Mathew J Suazo, Logan M Fenimore, John M Torkelson Covalent adaptable networks (CANs) may be synthesized by a variety of methods, with the most common being synthesis from monomers. Reactive melt-state processing provides a simple procedure for grafting dynamic crosslinkers onto precursor linear or branched polymers, also resulting in CANs. Reactive processing also allows for the direct examination of structure-property relationships between the precursor polymers and CANs. Here, we synthesized poly(n-hexyl methacrylate) (PHMA) samples of various molecular weights and prepared CANs via reactive processing to graft dialkylamino disulfide dynamic crosslinkers between PHMA side chains. We characterized how crosslinker loading and precursor molecular weight affected the rubbery plateau modulus (which is directly proportional to crosslink density according to Flory’s ideal rubber elasticity theory), stress relaxation time, and elevated-temperature creep resistance of the CANs. By comparing to a previous published study of PHMA CANs made by copolymerization of hexyl methacrylate with dialkylamino disulfide crosslinkers (with the crosslinkers attached to the chain backbone), we determined that the activation energies of stress relaxation and creep viscosity are the same within experimental uncertainty but a function of how the crosslinker is attached to the PHMA chains; the time and temperature conditions for reprocessing were also a function of the method of CAN synthesis. These outcomes demonstrate the importance of synthesis-structure-property-reprocessing relationships in CANs. |
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N00.00091: Design of Polymers With Orthogonal Gelation Schemes for Water-Soluble Photo-Patterned Release Layers Matthew Ticknor, Montana B Minnis, Erik Banta, Qi Lu, Ryan Hayward Photolithographic microfabrication, pervasive in semiconductor device fabrication, micro-electromechanical systems, and microfluidic channels, often involves sacrificial release layers that must be washed away with harsh chemical processing. Fabricated polymer-based microstructures, including stimuli-responsive surfaces, shape-morphing particles, and biomedical devices, may often not survive these steps, motivating the development of easily-removable release materials. Through controlled radical polymerization, we have synthesized water-soluble polymers with two orthogonal gelation mechanisms, one reversible and chemically driven, the other irreversible and photochemically driven. In solution, we first form Schiff bases between pendent benzaldehyde groups and diamine crosslinkers, yielding branched polymers that remain below the gel point. Next, in the solid-state, pendent benzophenone groups are used to photochemically crosslink the material, selectively forming gelled structures in irradiated regions that remain after unexposed regions are removed. After microfabrication of desired polymer structures, washing with a slightly acidic aqueous solution causes the photo-patterned release film to dissolve due to reversible dissociation of the Schiff base. We have studied how the content of the two crosslinking monomers and stoichiometry of diamine to benzaldehyde control the ability to reversibly cross the gel point, enabling effective use of this approach. |
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N00.00092: Room Temperature Repairable Dynamic Covalent Adaptable Network with UV Responsive Disulfide Bonds Yeomyung Yoon, Chae Bin Kim Dynamic network exchange reaction allows covalent adaptable networks (CANs) to be malleable and reprocessable analogue of thermosetting polymers. Typically, CANs rely on thermally activated network exchange reactions, necessitating high temperatures for their processing and repairing. This high-temperature requirement limits the range of applications for CANs, particularly those that need to be maintained under mild conditions. To address this limitation, in this poster, a new type of CAN that is responsive to UV light will be presented. This UV-responsive CAN can be processed and/or repaired at room temperature by simply exposing it to UV irradiation. Importantly, repairing this material is only achievable when UV irradiation is applied; it cannot be repaired without this step. Furthermore, the application of UV irradiation results in faster stress relaxation, demonstrating that UV exposure accelerates the dynamic exchange reactions within the CAN. This UV-responsive CAN innovation introduces new methods for processing and repairing CANs, making it particularly well-suited for applications that require repair under mild conditions. |
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N00.00093: Poster: How Do Ultrathin Polymers in the Softening Regime Fail? Ava Crowley, Konane Bay Molecular mobility can influence the low and high strain response of ultrathin polymer films. For glassy polymer films, the average molecular mobility contributes to the decrease in maximum stress and elastic modulus. While for polymer films in the softening regime, near or above the glass transition temperature, the confinement induced changes in mobility are associated with the opposite mechanical response, an increase in elastic modulus. Here, we directly measure the stress-strain response of freestanding poly(n-butyl methacrylate) (PBMA, MW = 180 kDa, Tg = 15ºC) as a function of temperature (T= 4 – 30 °C) and film thickness (30 – 300 nm). Below the glass transition temperature, the maximum stress and elastic modulus decrease with decreasing thickness, and as the temperature increases, we observe a transition in behavior where maximum stress and elastic modulus increase with decreasing thickness. These results provide new fundamental insight into how polymer behavior is altered due to changes in molecular mobility upon confinement. |
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N00.00094: How do crumples impact the stiffness of ultrathin polymer films? Lydia Flackett, Konane Bay, Ava Crowley Handling of polymer films becomes increasingly difficult as film thickness decreases. Liquid support layers are often used to ease the manipulation of these films. Here, we demonstrate that a hydrophilic polymer film, poly (methyl methacrylate), can be reversibly folded and unfolded from liquid surfaces resulting in crumples, creases, and folds forming in the film. We investigate the impact of film thicknesses and area on the resultant crumples and how crumples impact the mechanical properties. These results provide new fundamental insights into how polymer behavior is altered due to changes in the ultrathin film geometry upon crumpling the films. |
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N00.00095: Processing Effects on the Physical Properties of Ultrathin Glassy Polymer Films Emika Iino, Myounguk Kim, Alfred J Crosby, Toshiaki Ougizawa The physical properties of ultrathin polymer films with thickness less than 100 nm often differ from their bulk counterparts. Two factors are commonly associated with these changes as a function of film thickness. First, the chain mobility of polymers at interfaces is often different compared to that of polymers away from the interface. Second, higher-order structures controlled by the overlap concentration (C*), such as chain entanglements and free volume, can also be affected by dimensional constraints in ultrathin films. However, it has been unclear how these two factors are intertwined in the context of polymer processing methods. |
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N00.00096: Investigating Microphase Separated Triblock Copolymers as Vehicles for Targeted Mechano-responsive Materials Brandon Jeong, Antonia Statt In recent years, research on force-responsive molecules has grown, providing avenues for the development of mechano-responsive materials for a variety of applications. While there has been progress towards the development of many force-responsive molecules (mechanophores) with a variety of response mechanisms, sufficient fundamental understanding of force distributions in adequate bulk materials is currently lacking. Recent studies have shown that microphase-separated triblock copolymers are promising as mechanophore carriers over their elastomers due to their greater design space and increased activation efficiency. Here, we take steps towards exploring this design space using coarse-grained molecular dynamics simulations. We simulate a microphase separated triblock copolymer melt with periodic boundary conditions and incrementally elongating the system along one axis with isothermal-isobaric conditions to mimic experimental tensile deformation. We present our findings on the effect of mechanophore location along the chain on the bulk activation behavior using molecular-scale data gathered using simulations. |
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N00.00097: Polymer Crystallization in Nanoemulsion Systems Shichen Yu, Christopher Y Li Polymer crystalsomes are a new type of polymeric nanoparticles, which can form by crystallization at curved liquid/liquid interface of nanoemulsions. Previous work showed the polymer shell is single-crystal-like with a splayed lattice wrapped into a spherical shell whose size ranges from 100nm to several micrometers. The highly dynamic nanoemulsion system offers a unique opportunity to control further the crystalsome size, size distribution, and morphology, which are essential for their end applications. In this work, using poly(lactic acid) (PLA) as an example, we demonstrate that while polymer crystallization is confined mainly in the emulsion droplets, inter-droplet interaction, which often manifests itself as droplet coalesce or Oswald ripening, can also alter polymer crystallization pathways. Stabilizing nanoemulsion can lead to much-improved polydispersity of the crystalsomes. Possible polymer chain exchange was followed by blending nanoemulsions formed by the R and S enantiomer of PLA nanoemulsions. Our results reveal that nanoemulsion is a versatile platform for fabricating functional polymer nanoparticles and advancing our understanding of polymer crystallization. |
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N00.00098: Crystallization of molecular bottlebrushes bearing single- and double-crystalline side chains Carl Furner, Jeffrey T Wilk, Christopher Y Li, Bin Zhao, Ethan Kent, Michael Kelly Molecular bottlebrushes (mBBs) are an important polymer system for studying the architecture dependence of various phenomena, such as self-assembly and mechanical response. In this work, mBBs are employed as the model system to study the molecular structure and architectural effects on polymer crystallization. A grafting-to method was used to syntheisze mBBs bearing poly(ethylene oxide) (PEO) side chains, with grafting density ranging from 0.19-0.91. The effect of side chain grafting density on the nucleation and growth of PEO was decoupled in a series of non-isothermal and isothermal crystallization measurements. This system is compared with a 3-arm star bottlebrush synthesized from a 3-arm star PMA backbone to reveal the architectural effect. Furthermore, mixed mBBs with double crystalline side groups were synthesized to understand confined crystallization in mBBs. Poly(caprolactone) side chains are grafted alongside PEO side chains to achieve a random graft copolymer with high grafting density and varying side chain composition. Our study shows that the grafting density increases the melt-memory effect of side chains, backbone architecture reduces the growth rate of crystals grown from the melt, and that mixed grafted bottlebrushes follow some trends shown in block copolymer systems in nucleation order and confined crystallization. These three systems illustrate the broad range of properties attainable through architecture control in bottlebrush copolymers. |
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N00.00099: Entanglement Effect on Folding Behaviors of Semi-crystalline Polymer during Melt-Crystallization Zheng Huang, Toshikazu Miyoshi, Chenxuan Sun, Fan Jin In the earlier theoretical research, impact of entanglement on folding during crystallization was minimized. The combination of 13C isotope labeling and NMR spectroscopy allows us to quantitatively determine stem to stem distance as well as chain folding distance, hence, we are able to probe chain-level structure. Our recent work indicated that polymer chains are possible to fold prior to crystallization. In this poster, we would like to investigate the folding structure of a semi-crystalline polymer in melt-grown crystals (mgc) by using solid-state NMR spectroscopy and SAXS measurement. First, various 13C enriched poly(L-lactic acid) (PLLA) samples with different molecular weights (Mw = 2.5k – 300k g/mol) across critical entanglement length (Mc = 16k g/mol) were prepared in order to observe the molecular weight dependence of folding structure of PLLA. We revealed that entanglements influence the folding number during crystallization. Second, we attempt to observe the entanglement effect through diluting entanglement density, i.e., blending the PLLA above and below the Mc with different ratio and molecular weight. Based on the experimental results, we would like to highlight the impact of entanglements on folding of semicrystalline polymer in the melt-grown crystal. |
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N00.00100: Structure and Mechanical Property of Highly Branched Polyethylene Thermoplastic Elastomers Bohao Peng, Toshikazu Miyoshi, Keaton Turney, James Eagan Highly branched polyethylene (PE) thermoplastic elastomer (TPE)s can be synthesized using Brookhart-type α-diimine nickel and palladium catalysts, which show a range of branching number and identity. In this work, we aim at elucidating the structure-property relationship of various PE-TPEs through solution-state and solid-state 13C NMR spectroscopy and mechanical tensile testing. By applying solid-state NMR spectroscopy, DSC, and XRD, it was revealed that small degrees of crystallinity (< 5%) yields polyethylenes that are sufficiently reinforced to exhibit TPE behavior. Across PE samples with similar branching numbers, we relate the effects of branch identity, crystallinity, and molecular weight on the tunable mechanical properties. The structure-property relationship of the PE-TPEs will be discussed. |
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N00.00101: Molecular Level Study into Protonated and Deuterated Polyolefin Blends by Solid-State NMR WALTER G ROMANO, Bohao Peng, Toshikazu Miyoshi, James Eagan, Arsalaan Pathan, Zheng Huang Recycling different plastics post-consumers causes downgraded performance due to the physical and chemical property differences conflicting with one another. These properties stem from the incompatibility of the blends to crystallize and blend. As there are millions of tons of waste every year, the ability to effectively blend two plastics such as polyethylene and polypropylene becomes crucial. In this poster, a molecular-level study of polyolefin blend co-crystallization will be explored by utilizing solid-state NMR spectroscopy. It is through NMR spectroscopic techniques and the use of selectively activating various parts of the blend through isotopes that aspects of the arrangement can be made. We will conduct studies into the co-crystallization of the blends utilizing deuterated polymers to access the chain-to-chain interface differences. This will give us the ability to see the relative extent of interaction as well as providing overall system kinetics. From these experiments, a diagram of the co-crystallization structure can be made as well as a defined system to analyze crystallization. |
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N00.00102: Thin Film Crystallization of Molecular Bottlebrushes Carl Furner, Jeffrey T Wilk, Christopher Y Li, Bin Zhao, Michael Kelly Thin film crystallization of molecular bottlebrushes bearing semicrystalline poly(ethylene oxide) (PEO) chains has been investigated. The unique bottlebrush architecture results in rich crystalline morphologies in ultrathin films, including flat-on single crystals and fiber-like structures, with the fiber-like crystals being the predominant phase. This observed morphology sharply contrasts with the behavior of linear PEO, where flat-on crystals dominate in ultrathin films, and relatively thicker films typically exhibit edge-on crystals. The growth of these fiber-like crystals was monitored using in situ atomic force microscopy (AFM) and optical microscopy, which revealed anisotropic growth rates. A detailed chain packing mechanism will be discussed. Our findings underscore the significant influence of both the solid substrate's confinement and the tethering chain effect associated with the mBB architecture on the pathways of polymer crystallization. |
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N00.00103: Suppressing crystalline phases of liquid crystalline polymers Kirstin Bode, Chun Lam Clement Chan, Emily C Ostermann, Shawn M Maguire, Emily C Davidson Thermotropic liquid crystalline (LC) materials rely on temperature-dependent reversible transitions between liquid crystalline (e.g. nematic) and isotropic states. However, many mesogens that demonstrate LC phases as monomers do not show LC behavior in the polymer form; instead, they form semi-crystalline polymers whose crystallinity can inhibit the desired material response to stimuli. In order to suppress the crystallinity of the LC polymers, copolymers of LC mesogens and non-LC spacers were prepared by first synthesizing macromonomers via azide-alkyne click chemistry. These macromonomers were then polymerized to form polymers with known mesogen-to-spacer ratios. Wide-angle X-ray scattering (WAXS) and thermal characterization of the resulting polymers was then undertaken to determine the impact of spacer content and polymer composition on the crystallinity and LC phase transition temperatures of these materials. |
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N00.00104: A computationally-informed unified view on the effect of polarity and sterics on the glass transition in vinyl-based polymer melts Tianyi Jin, Connor W Coley, Alfredo Alexander-Katz We unveil a unified view on the effect of side chains on the glass transition temperatures (Tg) in polymer melts using molecular dynamics simulations, density functional theory calculations, and available experimental data. We use acrylates as a model system and evaluate the effect of n-alkyl side-chains on Tg. We find that backbone dihedral angle fluctuations follow established patterns due to sterics, as expected. However, we also find that the dihedral angle orthogonal to the backbone, which normally is neglected when discussing the effect on Tg, introduces a secondary rotational degree of freedom which impacts strongly Tg. These results are in agreement with experiments, and generalize to multiple other polymer systems, as is demonstrated using available experimental data. Conversely, n-alkyl pendant groups attached to the side group reduce Tg. Our work establishes a coherent framework that unifies previously established trends, emphasizing the polarity and size effects of n-alkyl chains on Tg. |
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N00.00105: Optical Fibers in Fluoropolymer Cladding Exhibiting Unixial Photomechanical Motion Louis D Ferreira, David R Sheffield, Nathan J Dawson, Matthew Knitter, Joseph Pusateri Stable and repeatable uniaxial pistons at any scale are desirable simple machines for a variety of applications. This study examines photomechanical behavior of optical fibers to actuate the motion exclusively with laser light. Sample fibers were fabricated by doping a polydimethyl-siloxane resin solution with graphene nanoplates and drawing that solution into fluoropolymer tubing before the resin set. When pumped by a continuous-wave laser, the graphene absorbs the light, heating the cured resin which expands within the tube and protrudes out the ends with uniaxial motion. Some of the resulting motion was due to the tube cladding itself expanding and straining from the heat, where the core was pinned to the fluoropolymer cladding. Successive samples were lubricated with a non-refractive castor oil to reduce friction and allow free motion between the core and cladding. The results presented examine the efficacy of adding lubrication to the system on its reversibility, and the contribution of variables such as sample length, variations of inner diameter, and cladding material in repeatability. |
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N00.00106: Molecular dynamics study on the stress-thermal relation of polymer melts under shear flows Kotaro Oda, Shugo Yasuda Understanding the thermos-rheological properties of polymer melts under external flows is quite important in polymer processing. The stress-thermal rule (i.e., the linear relationship between the thermal conductivity tensor and the stress tensor) has been proposed based on a network theory of polymer melts. Experimental and simulation studies have confirmed it indeed holds for the anisotropic parts of the thermal conductivity tensor and the stress tensor of polymer melts under deformation. However, as far as the authors know, there have been few reports on the polymer melt under shear flows, except for a single experiments. |
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N00.00107: Dynamic mechanical properties during formation and degradation of star polymer hydrogels Eleanor Quirk, Michael C Burroughs, Brendan M Wirtz, Tracy H Schloemer, Daniel N Congreve, Danielle J Mai
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N00.00108: Capillarity-Driven Pinching Dynamics and Extensional Rheology of Dilute and Entangled Polymer Solutions Cheryl L Slykas, Jorgo Merchiers, Carina Martinez, Louie Edano, Naveen Reddy, Vivek Sharma Concentration-dependent variation of macromolecular conformations and dynamics in polymer solutions are influenced by molecular weight, degree of overlap, solvent quality, and number density of entanglements. In this contribution, we characterize the shear and extensional rheology response of flexible polymer solutions using the broadest range of concentrations, spanning from ultra-dilute to highly entangled in solvent mixtures. We characterize the response to extensional flows realized in capillarity-driven pinching of a liquid necks by using the dripping-onto-substrate (DoS) rheometry protocols. The concentration-dependent variation in shear vs extensional rheology response reveals distinct influence of polymer and solvent properties. Lastly, we find standard predictions of FENE-P or Oldroyd-B models are inadequate to describe the observed radius evolution datasets. |
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N00.00109: Modeling Liquid-Solid Phase Transitions in Suspensions of Compressible Microgels Oreoluwa E Alade, Alan R Denton Microgels are soft colloidal particles, made of crosslinked polymer gels, whose internal degrees of freedom allow them to respond to external stimuli by changing size. Their sensitive responses to changes in temperature and concentration inspire practical applications, e.g., to drug delivery and photonic crystals. To explore the influence of particle compressibility on thermodynamic phase behavior, we modeled suspensions of microgels that interact via the Hertz pair potential and swell/deswell according to the Flory-Rehner theory of polymer networks. From extensive Monte Carlo simulations that incorporate novel trial changes in particle size [1], we determined the liquid-solid phase boundary (microgel density vs. crosslink density) by computing free energies, osmotic pressures, and chemical potentials of both liquid and solid phases via thermodynamic integration methods [2]. Our results significantly extend previous studies of the phase behavior of (incompressible) hertzian spheres [3]. We further computed latent heats of melting, radial distribution functions, and static structure factors. |
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N00.00110: Modeling the Response of Soft Microgels to Crowding by Nanoparticles Mahesh Aryal, Alan R Denton The internal degrees of freedom of crosslinked polymer networks enable compressible microgels to swell or deswell by absorbing or expelling solvent in solution. The presence of cosolvents or other macromolecules (e.g., nanoparticles) can enrich the swelling response, facilitating applications of “smart” colloidal particles, e.g., as drug delivery vehicles and biosensors. We extend the mean-field Flory-Rehner theory of polymer networks to incorporate, as an implicit species, hard nanoparticles that perturb the polymer network through volume exclusion. Within the free energy landscape of these asymmetric ternary mixtures, we perform Monte Carlo simulations, including novel trial moves [1] that allow microgels to change size and nanoparticles to penetrate microgels. Within our coarse-grained model, we investigate how single-microgel properties (e.g., crosslink density) and solution properties (e.g., microgel and nanoparticle concentrations, solvent quality) influence (1) partitioning of nanoparticles inside and outside of microgels; (2) swelling of microgels; and (3) bulk structure of microgel solutions. Our results can guide experiments and applications by providing insights into how the response of soft (e.g., biological) materials to external stimuli can be tuned by adding nanoparticles. |
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N00.00111: A Kinetic Model for Off-Stoichiometric Crosslinking Reactions of End-Linked Polymer Gels and Networks Haley K Beech, Tzyy-Shyang Lin, Hidenobu Mochigase, Bradley D Olsen The formation of end-linked polymer networks and dilute gels is commonly modeled as idealized chemical reactions resulting in defect-free networks. However, many widely used industrial processes including platinum-catalyzed vinyl-silane crosslinking of poly(dimethylsiloxane) (PDMS) are mechanistically complex and involve a variety of side-reactions. Here, a kinetic graph theory (KGT) model was updated to account for off-stoichiometric reactive groups and side reactions by adding two fitting parameters representing the relative rate of competing side reactions and the probability of side crosslinking events. Elastic effectiveness of the resulting network is calculated with the nonlinear Miller-Macosko theory (MMT), updated to account for side reactions and side crosslinking. Combined, the updated KGT and MMT provide elasticity estimates which capture the experimental peak in elastic modulus observed at an off-stoichiometric silane:alkene ratio in PDMS gels. This model is useful in systems where the crosslinking chemistry yields more complex reaction networks, making it relevant to many classes of polymer network chemistry where classical theories may not adequately capture network behavior. |
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N00.00112: Tuning Elastic and Viscoelastic Mechanical Properties of Double-Network Alginate-Polyacrylamide Hydrogels for Scaffold Design Applications Zhanda Chen, Vignesh Venkataramani, Cole Reinholt, Lydia Kisley Due to their soft consistency and unique physiochemical properties, synthetic hydrogel platforms are excellent candidates to construct 2D scaffolds for cell culture. However, the scope of hydrogel applications in tissue engineering is severely limited by poor mechanical properties and the lack of effective energy dissipation mechanisms. To overcome these limitations, double network hydrogels comprised of two interpenetrating gel networks offer remarkable fracture toughness and stretchability, whose properties can be exploited for rational scaffold designs. Here, we systematically study a series of alginate-polyacrylamide (Alg/PAM) double network gels with variable amounts of CaSO4 ionic crosslinker and cell adhesion molecule modifications. Based on both elastic (uniaxial tension) and viscoelastic (rheology, dynamic mechanical analysis) measurements, in combination with swelling experiments of the gels, we develop a unified model for understanding the molecular structure-property relationships to attain double network gels toward specific cell culture applications where such desired physical properties as elastic modulus, extensibility, and stress relaxation are required. |
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N00.00113: Effect of Kinetically-Distinct Crosslinking on Temporal Mechanical Property Development in Photopolymerized Networks Rithwik Ghanta, Cade McAndrew, Alexa S Kuenstler The degree of crosslinking in polymer networks dictates key mechanical properties including stiffness, toughness, and self-assembly. Crosslinking density has been patterned to form multi-materials with local variations in mechanical properties. This patterning can be achieved through a material system where crosslinking density can be varied with light dose. Thiol-ene click chemistry occurs under light-induced radical polymerization and has the potential for tunability. In addition to being consistent, high yield, and stereoselective, prior work has shown thiol-ene systems are controllable with judicious choice of thiol and ene monomers. In this work, we investigate the kinetics of various ternary thiol-ene systems as a function of light exposure. Using 1H-NMR spectrometry and Fourier Transfer Infrared (FTIR) spectroscopy, we measure functional group conversion at various illumination times, probing the kinetics of thiol addition to both internal and terminal ene groups. In our investigation, we elucidate how steric hindrance, isomerization, and monothiol structure act in the radical addition. We find that thiols will preferentially add to terminal ene groups, and trans-oriented internal acrylate groups homopolymerize on a similar time scale. We correlate these kinetics to the crosslinking density of polymer networks formed using dithiols in this ternary system and the emergent mechanical properties. Ultimately, we present a methodology to directly correlate mechanistic studies of polymerization to bulk physical properties, which is anticipated to have applications in additive manufacturing and designer polymer networks. |
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N00.00114: Crack formation in end-linked polymer networks Devosmita Sen, Kanon Hasegawa, Bradley D Olsen Macroscopic fracture of polymer networks is linked to the molecular behavior of chains within the network, yet the fundamental molecular-level processes that lead to nucleation of a crack and its subsequent propagation remain elusive. Damage zones can be very widely spread in a network containing topological defects, suggesting that there is a finite volume of fracture zone around the crack tip associated with the initiation of the crack, in contrast to the simple assumption of a sharp crack plane. Recent studies have revealed that depercolation of the fracture zone is a necessary criterion for crack propagation. However, the size of this fracture zone is not yet accurately known. To better understand the initiation of fracture, coarse-grained simulations are performed on end-linked networks containing a blend of “weak” polymer chains in a matrix of unbreakable “strong” chains. Chain breaking is studied as a function of the extent of tensile deformation for networks with varying ratios of weak chains below and above the percolation threshold to reveal the extent of localization of chain scission within specific network clusters. As the network is stretched, a series of such chain breaking events lead to depercolation of the fracture zone, eventually leading to macroscopic failure of the material. |
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N00.00115: Scaling in Gel Mechanics: Crossover between Self- and Neighbor-Avoiding Walks Nobu C Shirai, Naoyuki Sakumichi Recent studies on rubber-like polymer gels have highlighted a phenomenon termed "negative energetic elasticity," suggesting that elasticity is not solely derived from entropic contribution. Building on this understanding, we investigate the crossover between the self-avoiding walk (SAW) and the neighbor-avoiding walk (NAW) on a cubic lattice [Phys. Rev. Lett. 130, 148101 (2023)]. This crossover provides insights into the behavior of a single polymer chain within a broader context of polymer gels. Through exact enumerations for steps up to n=20, we clarify the behavior of negative energetic elasticity associated with this crossover. One of the main results of our study is the universal scaling relation between TU∞ and the chain slack, represented as n-r. In this context, TU∞ emerges as the theoretical counterpart of the experimentally observed TU, a consistent measure of normalized polymer concentration. This universal scaling exponent sheds light on the mechanics of polymer gels, especially the behavior related to negative energetic elasticity. Our study provides a comprehensive understanding of the mechanics of polymer gels and offers potential directions for future research in gel elasticity. |
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N00.00116: Crosslink-to-Entanglement Transition and Crosslink Fluctuations in Polymer Networks Yuan Tian, Zilu Wang, Michael S Jacobs, Andrey V Dobrynin We use coarse-grained molecular dynamics simulations to study the mechanical properties of networks with different degrees of polymerization (DP) between crosslinks. The simulations show that there is a transition from crosslink- to entanglement-controlled network elasticity with increasing DP of network strands, nx, which is manifested in changes in the nx-dependence of entanglement and structural shear moduli. In particular, this crosslink-to-entanglement transition results in saturation of the network shear modulus at small deformations and renormalization of the DP of effective network strands determining nonlinear elastic response in the strongly entangled networks with nx >ne (DP of the network strand between entanglements). This crosslink-to-entanglement transition can also be observed from qualitative changes in the time evolution of the correlation function <(R(t+τ)-R(t))2> describing crosslink fluctuations. At short time scales, this function reflects Rouse dynamics of crosslinks, while at longer time scales, it saturates to a constant. The constant value scales linear with the DP of network strands between crosslinks nx for nx <ne. However, for strongly entangled networks (nx >ne), the plateau saturates with increasing DP between crosslinks, nx. |
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N00.00117: Molecular Dynamic Simulation of Free Polymer Chain diffusion into a Regular network. Jude Ann Vishnu, Sebastian Seiffert, Friederike Schmid Core-shell polymer gels are a type of smart material that have received increasing attention in the recent years due to their application in medical field. Here we present a coarse-grained MD simulation study of the inter-diffusion of symmetric system of polymer gel (core) and polymers (shell). We discuss the affect of polymer concentration on inter-penetration and its effect on polymer orientation near the gel-polymer interface. A consequence of this is also seen on the diffusion constant on polymers near gel-polymer interface. Further we extend our study to understand the inter-facial properties like inter-facial width and inter-facial tension by varying the concentration of diffusing polymers. |
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N00.00118: Deformation of Brush Gels and Hidden Length Zilu Wang, Sergei Sheiko, Andrey V Dobrynin Brush gels demonstrate unique mechanical properties when compared to gels of linear strands. Using a combination of molecular dynamics simulations and theoretical analysis, we study mechanical properties of brush gels which strands are made of solvophobic backbones and solvophilic side chains. In poor solvent conditions for the brush backbones, backbones collapse creating reservoirs of the hidden lengths. The degree of backbone collapse is determined by a fine interplay between surface energy of the collapsed backbone and steric repulsion between side chains. The conformations of the brush strands are studied as a function of the degree of polymerization and grafting density of the side chains and solvent quality for the brush backbone. It is shown that the brush strand conformations are directly related to the gel swelling ability. For bottlebrush-like strands, the side chains screen and dilute backbones resulting in the large gel swelling ratios and weakening sensitivity to changes in solvent quality for the backbone. In contrast, for gels with comb-like strands, solvent quality has a pronounced effect on the backbone conformations creating reservoirs of hidden lengths and allowing such gels to sustain extremely large reversible deformations. |
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N00.00119: Coacervation in dilute charged polymer solution Jae Wan Chung, YongJoo Kim Coacervate is dispersed droplet of dense phase, liquid-liquid phase separation of oppositely charged polymer in a mixture of polymer solution. In this study, phase behavior of oppositely charged polymers were investigated as functions of charged polymer length (15,30,45,60) and concentration of counterions in dilute polymer solution limit. Two types of linear polymer chains, which is charged in all positive and all negative, exist in the same number with different concentration of counterions in the simulation box. We observed coacervation and dispersion of polymers upon a change in concentration of counterions. Also, depending on the chain length of the charged polymer, the concentration of counterions at which dispersion occurs is slightly different. Molecular dynamics simulations suggested the dispersion of charged polymers according to counterions, which satisfy the local electrical neutrality of charged polymers. We can observe coacervate in dilute solution limit when the counterion's local influence is small. |
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N00.00120: Counterion distribution around the strongly stretched polyelectrolyte chains: from single molecules to hydrogels Aykut Erbas, Muzaffar Rafique Using all-atom molecular dynamics simulations of a polyacrylic acid chain in explicit water as a model system, we calculated the counterion distribution and condensation profiles around the stretched (weak) polyelectrolyte chains. The condensation under deformation is highly non-monotonic. Ionic condensation around the chain increases as the chain is stretched strongly up until its contour length. This increase reaches a maximum and decreases as the chain is stretched beyond its counter length. A Manning-type condensation behavior can explain the latter case. However, in moderate stretching, condensation changes with solvent distribution around the chain. If chains are crosslinked by their ends to form a polyelectrolyte hydrogel, this unexpected stretch-dependent phenomenon leads to a deformation-dependent counterion condensation in the polyelectrolyte hydrogel. Our results suggest that counterion condensation around polyelectrolytes can exhibit a rich behavior of electrostatic response under deformation. |
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N00.00121: Electrospinning of fouling-resistant non-woven fibrous filtration membranes from PVDF/Polyampholyte blends Anuja S Jayasekara, Ayse Asatekin, Peggy Cebe, Luca Mazzaferro, Ryan O'Hara Poly (vinylidene fluoride) (PVDF) is widely used in filtration and waste-water treatment applications due to its excellent mechanical, chemical, and thermal stability. However, its inherent high hydrophobicity leads to membrane fouling. One way to increase fouling resistance is to improve the hydrophilicity of PVDF-based membranes through blending with more hydrophilic polymers. Our research investigates blends of PVDF with polyampholytes, amphoteric macromolecules with positive and negative ionic groups showing excellent hydrophilicity. Fouling resistant non-woven fibrous membranes were fabricated using electrospinning of PVDF and a random polyampholyte copolymer (r-PAC) blended at different concentrations. r-PAC is synthesized by randomly co-polymerizing three monomers that are either hydrophobic (2,2,2-trifluoroethyl methacrylate); positively charged ([2-(methacryloyloxy) ethyl]trimethylammonium chloride); or negatively charged (methacrylic acid). The obtained fiber mats were characterized by wide angle X-ray scattering, Fourier-transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and scanning electron microscopy. Sessile drop contact angle measurements were used to evaluate the surface wettability of the membranes. Membrane fouling was assessed by fluorescent Bovine Serum Albumin (BSA) absorption tests. |
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N00.00122: Coarse-grained molecular dynamics simulations to study effect of cation charge density in polymer electrolytes Spand B Mehta, Lisa M Hall
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N00.00123: Hexagonal Boron Nitride Modulates Crystallinity and Charge Mobility in PEO–NaNO3 Electrolytes Colby Snyder, Shreyas S Pathreeker, Georgios Papamokos, Russell J Composto Composite polymer electrolytes (CPEs) hold great promise for the development of safe and sustainable batteries. In this study, we find that 2D hexagonal boron nitride (h-BN) has a non-monotonic effect on polymer crystallinity and total ionic conductivity in PEO-NaNO3 electrolytes. The dual Lewis acidity and basicity of h-BN allow it to interact with dissociated salt ions and the polymer matrix itself. PEO crystallinity was quantified using differential scanning calorimetry (DSC) and X-ray diffraction (XRD), and complex formation between NaNO3, PEO, and h-BN was studied using IR spectroscopy. Total ionic conductivity was determined using electrochemical impedance spectroscopy (EIS) as a function of temperature. We find that h-BN has two competing effects on polymer crystallinity and charge mobility in CPEs: 1) nucleation-enhanced crystallization of PEO on h-BN surfaces at low h-BN loading, and 2) spherulitic confinement of PEO at higher h-BN weight loading. DFT calculations confirm strong attractive interactions between h-BN and both free ions (Na+ and NO3-), and we also find lesser attractive interactions between h-BN and PEO. These new findings for Na-polymer electrolytes support our experimental results. Our findings highlight the importance of filler geometry and chemical characteristics in designing CPEs for Na-ion batteries. |
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N00.00124: Mechanisms of Ion Transport in Lithium Salt-Doped Zwitterionic Polymer-supported Ionogel Electrolytes Meron Y. Tadesse, Zidan Zhang, Nico Marioni, Everett S Zofchak, Tyler J Duncan, Venkatraghavan Ganesan, Venkatraghavan Ganesan Recent experimental results have demonstrated that zwitterionic (ZI) ionogel comprised of ZI polymer-supported lithium salt-doped ionic liquid exhibits improved conductivities and lithium transference numbers than the salt-doped base ionic liquid (ILE). However, the underlying mechanisms of such observations remain unresolved. In this work, we pursued a systematic investigation to understand the impact of the ZI content and salt concentration on the structural and dynamic properties of the poly(MPC) ionogel of our model ZI ionogel, ZI poly (2-methacryloyloxyethyl phosphorylcholine) (polyMPC) supported LiTFSI/N-butyl-N-methylpyrrolidinium (BMP) TFSI base ionic liquid electrolyte. Our structural analyses show strong lithium - ZI interaction consistent with the physical network characteristic observed in the experiments. An increase in ZI content causes the ionic liquid (IL) environment to resemble a neat ionic liquid due to lithium ions partitioning into the ZI polymer phase. In contrast, an increase in salt concentration led to the IL environment resembling a salt-doped ionic liquid. The diffusivities of the mobile ions in the poly(MPC) ionogel were found to be lower than the base ILE in agreement with experiments at T$>$300 K. Analysis of ion transport mechanisms shows lithium ions within the poly(MPC) ionogel travel via a combination of structural, vehicular diffusion as well as hopping mechanism. Lastly, the conductivity trend crossover between the poly(MPC) ionogel and the base ILE was rationalized via a temperature study that showed that the base ILE ions are influenced more by the variation of temperature when compared to the poly(MPC) ions. |
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N00.00125: Rapid and highly selective ion conduction via decoupling ion transport from polymer segmental relaxation in single-ion-conducting, polymer blend electrolytes Mengying Yang, Thomas H Epps The inherent trade-off between rapid polymer segmental relaxation and sufficient free lithium ion is known to constrain conductivity enhancements and therefore limit overall performance. The decoupling of ion transport from polymer segmental dynamics is promising to break this inherent anticorrelation. In this work, we blended a glassy single-ion-conducting (SIC) polymer, poly[lithium sulfonyl(trifluoromethane sulfonyl)imide methacrylate] (PLiMTFSI), with a flexible polymer, poly(oligo-oxyethylene methyl ether methacrylate), at various compositions. We connected the ion transport mechanism to the packing efficiency of polymer chains and investigated the composition-dependent thermal and conductive properties via differential scanning calorimetry, alternating current impedance spectroscopy, and dynamic mechanical analysis. High ionic conductivities approaching 1 × 10-2 S/cm were realized as a result of this decoupled ion transport. Additionally, immobilized TFSI- resulted in high Li+ selectivity (Li+ transference number = 0.9), electrochemical stability (up to 4.7 V against Li+/Li, and limiting current density (1.8 mA/cm2), which exceeds many solvent-plasticized SIC polymer electrolytes. |
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N00.00126: Conductivity and Transference Numbers in Lithium Salt-doped Block Copolymeric Ionic Liquid Electrolytes Zidan Zhang, Jakub Krajniak, Jacob Sass, Harnoor S Sachar, Nico Marioni, Tyler J Duncan, Venkatraghavan Ganesan We present multiscale molecular dynamics simulation results comparing the conductivity and transference numbers in lithium salt-doped polymeric ionic liquids (PolyILs) and the lamellar phases of block copolymeric ionic liquids (coPolyILs). In both systems, the anion mobilities decreased with salt loading. Lithium ions exhibited negative mobilities in both systems, but the magnitudes decreased with increase in salt concentrations. More interestingly, the anion mobilities were lower in the lamellar systems compared to homopolymers in magnitude, but the lithium ion mobilities and the transference numbers were less negative in such systems. We examine the anion-cation and lithium-anion interactions in terms of radial distribution functions, coordination characteristics and ion pair relaxation timescales. Based on such analyses, we rationalize the salt concentration dependencies as a result of the interfacial interactions in lamellar systems, and the competition between anion-cation and lithium-anion interactions in both PolyILs and coPolyILs. Overall, the findings presented in this study demonstrates that the modified anion-cation and lithium-anion interactions in the microphase separated coPolyILs may provide a strategy for realizing higher lithium ion transference numbers relative to the homopolymeric counterparts. |
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N00.00127: From Fully Stretched to Collapsed: Bottlebrush Polymer Chain Dimensions when Grafted to Nanoparticles Jensen Sevening, Robert J Hickey Polymer composites are used abundantly in daily life for their unique ability to improve material properties and diversify applications. Polymer grafted nanoparticles (PGNs) have been key to controlling targeted filler dispersion, which is essential for material performance. Thus far, studies on PGNs have been limited by the narrow scope of polymer chemistry and architecture, focusing on linear glassy chains. Macromolecular architecture plays a significant role in controlling material properties, but surprisingly, there are few examples of non-linear polymer chains grafted to nanoparticle surfaces. Here, the presentation will discuss drastic changes in polymer chain dimensions for bottlebrush polymer grafted nanoparticles synthesized via surface-initiated ring-opening metathesis polymerization (SI-ROMP). Bottlebrush PGNs display a substantial change in brush height, which is dependent on environmental conditions. In solvent, the brush heights are consistent with fully extended bottlebrushes, seen in dynamic light scattering (DLS) and cryo-transmission electron microscopy (TEM). In the melt, the brushes collapse on the particle surface, seen in TEM and ultra-small angle X-ray scattering (USAXS). These extreme polymer chain conformational differences with respect to condition have not been observed in linear architectures and is expected to influence self-assembly and the properties of the materials. |
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N00.00128: Nanofillers based on graphene derivatives for reinforcing polyurea coatings Gladys Shi Xuan Tan, Siyu Chen, Daria V Andreeva Polyurea is a well-known elastomer that is widely used as a protection coating due to its excellent mechanical properties and strong impact absorption. As a coating, it can be sprayed on to retrofit structures and thereby alleviate the damage by high-velocity impacts. Mechanical properties such as strength and damping are surrogate factors that determine their effectiveness. However, commercially purchased polyurea has its limits and superior mechanical properties of polyurea are desired such that it can withstand higher loads while at the same time, constructively being able to dissipate energy. Over the years, studies have shown that the use of nanofillers has played an imperative part in increasing the mechanical properties of polymeric coatings. In this work, amine-terminated polymers and isocyanates were reacted to form urea bonds with both soft and hard segments of the polyurea coating. Two-dimensional materials, i.e. graphene oxide (GO) and its derivatives were used as nanofillers to study the effect of the nanofillers in strengthening the mechanical properties. This study offers meaningful insights for designing functional coating that can be effectively used as a coating with the use of nanofillers. |
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N00.00129: Asymmetric Nanoparticle Interaction with Nematic Liquid Crystals Xiaowi Wang Liquid crystals (LC) have attracted a lot of attention due to their unique properties. Such as the discernible orientational ordering unveiled the coveted feature of anisotropic structure greatly popular within the display applications. Due to this feature, introducing particles into the LC system greatly demand in controlled soft matter applications, causing distortions in LC long-range order and shaping particle orientation. Extensive studies focused on spherical or geometric-dependent particles, size, surface anchoring, and LC elasticity while limited studies have investigated asymmetric shape particles. Additionally, Recent notably research on living liquid crystals observes controlled bacterial interactions, yet LC's biocompatibility limits understanding of bacterial shape or mobility's impact. In this study, we explore interactions involving synthetic asymmetric nanoparticles within an LC cell. The gold tadpole nanoparticles are introduced into the LC system to investigate the long-range-order defects and distortions. 5CB(4-Cyano-4'-pentylbiphenyl) were originally mixed with nanoparticles in different diameter and tail length then injected into a planar and hybrid cell. Due to the LC's birefringence properties, a polarized microscope was used to track LC field deformations caused by these nanoparticles. Notably, the unique "butterfly" patterns emerged within the distorted LC due to the interaction between these asymmetric gold tadpole nanoparticles and 5CB. Additionally, the air bubble also detected trailing these particles across samples of various sizes and cell conditions. Consequently, These external variables can control the distorted LC field formation and influence the anisotropic motion of the tadpole particle |
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N00.00130: Isothermal Compressibility of Azobenzene-Containing Epoxy-Amines Measured Using Small-Angle X-ray Scattering Frederick L Beyer, Joseph M Dennis The fracture behavior of polymers shifts from a brittle to ductile response as the environmental temperature cycles from below to above the glass transition temperature (Tg). The ability to rapidly transition through a Tg-like response using an external stimulus is a proposed mechanism by which mechanical properties of a polymer could be temporarily switched, depending on the needed response of the material. This capability could allow a strong, high-Tg polymer with the ability to “switch-on” Tg-like motions when desired. One method for inducing a Tg-like response may be the introduction of molecular motion in the glassy polymer through azobenzene isomerization. Azobenzene isomerization, which is a light-triggered molecular motion, may be sufficient to locally deform the network and encourage long-range chain cooperativity, and thereby transform the glass into a rubber. Isothermal compressibility, an intrinsic materials property often considered to be the inverse of elastic modulus, would be expected to increase if illumination causes the material to soften due to photoisomerization of azobenzene. In this presentation, results will be presented from a recent study in which small-angle X-ray scattering (SAXS) was used to measure isothermal compressibility of azobenzene-containing epoxy-amine networks with and without UV illumination |
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N00.00131: Incorporating metals and halogens into polypeptoid-based photoresists for extreme ultraviolet lithography. Cameron P Adams, Chenyun Yuan, Christopher K Ober, Rachel A Segalman Polymers have long played a critical role in patterning silicon to create microelectronic devices. However, as state-of-the-art “extreme ultraviolet” (EUV, 13.5 nanometer wavelength) photolithography tools now allow for patterning of sub-10 nm features, polymeric photoresists face significant challenges with stochastics and sensitivity. To address these, we have developed polypeptoid-based photoresists to investigate the effects of polymer sequence and dispersity on patternability. In traditional polymeric systems, dispersities in molecular weight, composition, and sequence are compounded by material inhomogeneities in photoresist formulations and poor EUV photon absorption, contributing to unacceptable patterning defects. Sequence specificity of the peptoid system eliminates these variations, enabling precise study of the effects of polymer sequence and dispersity on patternability. Incorporation of metals and halogens probes the impacts of strongly EUV-absorbing elements on photoresist sensitivity at industrially relevant conditions. |
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N00.00132: Relating Dewetting and Molecular Forces of Sandwiched Ultrathin Polymer Films Tera Huang, Evon Petek, Reika Katsumata Previous research has demonstrated that wettability and surface tension of polymer films often possess thickness dependence originating from underlayer effects and material property changes due to nanoconfinement. However, critical thicknesses at which the wetting behavior deviates from the bulk values are reported to be ~ 100 nm, which is an order of magnitude larger than van der Waals potential’s prediction. To investigate this discrepancy, we develop a tri-layered system consisting of a bottom layer of bulk polystyrene (PS, 450 nm thick), a middle of polymethyl methacrylate (PMMA, 15~150 nm thick), and a dewetting PS (20 nm thick) top layer. This system allowed us to investigate the evolution of the spinodal dewetting PS layer pattern over time as a function of PMMA middle layer thickness. Our results reveal that the spinodal pattern is influenced not only by the annealing time but also by the thickness of the middle PMMA layer, suggesting that molecular interactions can propagate the distance comparable to the middle layer’s thickness. We will further discuss the physical parameters, such as Hamaker constant, derived from Fourier transform of obtained images. This study presents an opportunity to modulate the surface wettability of polymer thin films without altering the surface chemistry, simply by the underlayer. |
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N00.00133: Sustainable Superhydrophobic PVDF-grafted Cellulose Membrane for Oil/Water Separation Yoon Huh, Joona Bang Herein we report a facile preparation of superhydrophobic poly(vinylidene fluoride)-grafted cellulose membranes (PVDF-g-CM) for oil/water separation. To provide the durability of membranes, PVDF was covalently bonded to the cellulose membrane via the surface-initiated reversible addition-fragmentation chain transfer/macromolecular design via the interchange of xanthates (RAFT/MADIX) polymerization. The resulting PVDF-g-CMs were characterized by Fourier transform infrared spectrometer, X-ray photoelectron spectroscopy, and water contact angle measurements. The oil/water separation performance was examined using various oils, including n-hexane, chloroform, toluene, diethyl ether, dichloromethane, and silicone oil, and the membranes exhibited excellent performance with separation efficiency higher than 97% for all oil/water mixtures. More importantly, due to the covalently bonding of PVDF on the surface, the PVDF-g-CMs showed superior stability under various environments, including water, oil, and acidic solutions, enabling them for practical application of oil/water separation. |
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N00.00134: Defect Healing in Graphene via Rapid Thermal Annealing with Polymeric "Nanobandage" Claire Senger, Xiao Fan, James Nicolas M Pagaduan, Xiaoyu Zhang, Muhammad Awais Fiaz, Jinglei Ping, Shawna Hollen, Reika Katsumata As defect introduction in graphene from synthesis and characterization processes is unavoidable, it is crucial to establish a new defect-healing method for graphene in post-silicon device fabrication. Current healing methods, such as conventional thermal annealing, are either time-consuming, highly specialized, or tedious. To this end, we have developed a new time- and energy-efficient healing approach for graphene, utilizing polymer-assisted rapid thermal annealing (RTA). In this method, a nitrogen-rich, polymeric "nanobandage" is coated directly onto graphene and processed via RTA at 800 ℃ for 15 seconds, successfully doping nitrogen into graphene. To understand its mechanism at an atomic level, we further investigate the nature of the defects and the location of the inserted nitrogen using scanning tunneling microscopy. This poster elaborates on how the nitrogen dopants bond with the graphene, augmented by in-situ mass spectroscopy to monitor the fragmentation of the nanobandage polymer during RTA. |
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N00.00135: Genomic analysis in a solid state nanopore device using single-strand binding proteins Alexander R Klotz, Victor Corona, Nathan Howald
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N00.00136: Mesoscale Simulations of Anisotropic Patchy Nanoparticles at Oil-Water Interfaces Grant R Kolacny, Abelardo Ramirez-Hernandez, Carlos Salinas-Soto, Esteban Urena-Benavides Cellulose is the most abundant organic material on earth, driving research for the production and use of cellulose-derived nanocrystals as Janus-particle emulsifiers. This study aimed to develop and use a mesoscale model of cellulose nanocrystals to better understand their emulsion stabilization mechanism and organization at the oil-water interface. Cellulose nanocrystals were modeled by anisotropic patchy particles consisting of two hydrophobic and four hydrophilic patches according to the experimentally-inferred structure. These nanoparticles were placed at an oil-water interface, and the effect of nanoparticles length and surface concentration on the interfacial tension and surface pressure were investigated. Interfacial tension was shown to be consistently reduced with increasing surface concentration of nanoparticles, with nanoparticles length having little influence on the final interfacial tension values. Nanoparticle organization was quantified by computing the nematic order parameter, S, at the interface. It was found that nanoparticles organize into rafts that have strong local orientational correlation, but rafts are randomly oriented at the interface, given place to a low global orientational correlation. |
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N00.00137: Epoxy-Cellulose nanocrystals composites with cholesteric sturcture Rebecca (Sujin) Lee, Marcos A Reyes-Martinez, Edwin P Chan, Jeremiah Woodcock This study presents an chemical modification of cellulose nanocrystals (CNCs) to generate chiral nematic CNC-epoxy composites. The surface of CNC was decorated with epoxide groups via reaction with epichlorohydrin (EPH). With increased hydrophobicity of the surface, CNC mixture was well-blended with butanediol. The CNC/epoxy hybrid films retain the photonic characteristics of the CNCs host. The effect of epoxy concentration on the structure, optical properties, and mechanical properties were examined within this study. The method of modification and the unique properties of the modified CNC (hydrophobicity, crystallinity, reinforcing ability, and optical activity) render them a novel bionanomaterial for a range of multipurpose applications. |
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N00.00138: Modeling In Vitro Hyaluronan Synthesis by Non-processive Enzymes Jan Scrimgeour The giant biopolymer Hyaluronan (HA) is commonly synthesized in the membrane of living cell by highly processive enzymes. Given hyaluronan’s use as a medial lubricant, cosmetic ingredient, and treatment for joint pain there has been significant research aimed at gaining control over hyaluronan size and polydispersity during lab-based synthesis to optimize the physical and therapeutic properties of the synthesised material. Of note in this work, is the ability of synthesis enzyme from the bacterium P. multocida to catalyze HA synthesis in a non-processive manner during in vitro reactions [1]. When reactions are seeded with short HA primers this enzyme has demonstrated the ability to produce a highly monodisperse product. While this behavior has been qualitatively attributed to the strong preference for extension of existing product over the formation of new product, there is no quantitative model that explains this behavior. I present kinetic models that describe these in vitro synthesis reactions. Simulation of the reactions allows investigation of the systems’ behavior under a wide range of conditions, including prediction of reaction outcomes. Conditions that reproduce the behavior observed in previous experiments are identified and the results will support ongoing investigations into more complex one-pot synthesis schemes for HA. |
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N00.00139: Poloxamer Gels in Biocompatible Ionic Liquids to Treat Middle Ear Infections Colin K Houts, Charles Knisely, Arit Das The current standard of care for otitis media (OM, middle ear infection) has many limitations including contribution to bacterial antibiotic resistance and unwanted side-effects. Recent research has highlighted the potential of aqueous, drug-loaded poloxamer gels (composed of hydrophilic and hydrophobic blocks) for treating OM. These formulations can be directly administered onto the eardrum for targeted, non-invasive drug delivery. However, small-molecule chemical permeation enhancers (CPEs) must be added to the poloxamer gels to enable drug transport across the eardrum, making formulation difficult. Choline-based ionic liquids (IL) are a potential solution to this problem as they are stable, biocompatible, and can serve as both a solvent and CPE. In this work, the interactions of biocompatible poloxamers and choline-based IL are investigated to fine-tune the rheological and structural properties of the drug delivery system. Poloxamer in choline-hexenoic IL and water was shown to transition to a gel state upon heating with a corresponding gel structure of body-centered-cubic (a = 83.5 A). The anion-to-cation ratio of IL and poloxamer concentration were varied to analyze its effect on sol-to-gel transition and associated final gel structure. The results obtained from this study can be exploited to develop more effective drug delivery routes to treat OM. |
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N00.00140: Beyond alignment: a novel mechanism for developing well-ordered block copolymer materials via low-intensity magnetic fields Grace Kresge, Christopher A Neal, Michelle A Calabrese Prior work in the directed assembly of block copolymers (BCPs) via magnetic fields has primarily relied on the alignment of BCP chains or phases in bulk. In this work, the application of low-intensity magnetic fields (B ≤ 0.5 T) to poloxamer solutions yields a remarkable solvent-mediated disorder-to-order transition, not reliant on alignment mechanisms. In situ magneto-rheology demonstrates this ordering transition is accompanied by substantial increase in shear modulus, surpassing the effects of thermally-induced ordering by several orders of magnitude. Subsequent magnetization induces order-to-order transitions, from cubic to cylindrical micelle packings. The mechanism underlying this ordering behaviors is illuminated via a combination of magnetorheology, small- and wide-angle X-ray scattering, differential scanning calorimetry, and vibrational spectroscopy. This study further quantifies significant reductions in micelle size and aggregation numbers when compared to temperature- and concentration-induced ordering. Overall, low-intensity magnetic fields (B-fields) exert a profound influence on polymer-solvent interactions within this aqueous BCP system, providing the driving force for this anomalous magnetically-induced ordering. |
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N00.00141: Understanding the effect of morphology of hydrophobic polymers on ion selectivity Eric Palacios Pineda Ion exchange membranes (IEM) have been used to separate ions from water, and to separate different types of ions. However, the selective transport of ions of the same charge, such as chloride and nitrate, is not optimized. In our previous work, we showed that coating IEM with a layer of polypyrrole, a conductive polymer, is effective in improving the selectivity between nitrate and chloride. We hypothesize that further improvement of ion selectivity can be achieved by controlling polypyrrole structure, such as tuning the polymer morphology and charge distribution. We use molecular dynamics to investigate the effect of polypyrrole morphology on the selective transport of same-charged ions. We elucidate how polypyrrole morphology influences the partition and diffusion of same-charged ions in the membrane by analyzing the ion diffusion, the dynamic pore size of the polymers, ion hydration and interaction energy landscape. The research sheds light on how to tune morphology of polymeric coatings to achieve high ion selectivity between same-charged ions. |
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N00.00142: Simulation Study of Self Assembly of Block Copolymers upon Solvent Evaporation Juhae Park, Ludwig Schneider, Juan J De Pablo Block copolymers (BCPs) have great technological potential due to their capacity to generate uniform and periodic nanoscale structures through microphase separation depending on the composition, and the segregation strength. For membranes applications, BCPs provide a bottom-up approach to form isoporous membranes that are useful for ultrafiltration processes involving functional macromolecules, colloids, and water purification. Isoporous BCP membrane fabrication occurs by evaporating solvent particles from well-mixed solutions of asymmetric BCPs and solvents in film states, and micro-phase separated structures propagate throughout the film. While the self-assembled structure of block copolymers in bulk systems has been extensively studied, the morphological changes of these block copolymers during solvent evaporation have not been fully explored. |
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N00.00143: SOFT MATTER PHYSICS
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N00.00144: Bridging Ability of Telechelic Polymers Control Linked Emulsion Structure and Rheology Daniel Keane, Ryan Poling-Skutvik Telechelic polymers—polymers with functional endgroups—serve as effective rheological modifiers in colloidal suspensions, enhancing fluid strength and elasticity. In this work, we utilize the telechelic, triblock copolymer polystyrene-b-polyethylene oxide-b-polystyrene (SEOS) to induce network formation in cyclohexane-in-water emulsions. The endblocks of SEOS will partition into the droplets while the midblock remains in the continuous phase, such that each polymer chain will either loop on a single droplet or bridge between two droplets. Based on the polymer molecular weight, the endblock partition strength and the likelihood of the chains forming bridges varies. Using nonlinear rheology and confocal microscopy, we investigate the effects of these differences in polymer bridging strength and density on the emulsions’ microstructures and yielding mechanisms. We relate the yielding behavior to the heterogeneity of bridging in the system, which results from kinetic trapping and multibody effects. These findings can aid in the design of novel soft materials for applications ranging from 3D printing to biomedical scaffolds. |
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N00.00145: Oil-water-poloxamer emulsions for non-invasive treatment of otitis media Charles T Knisely, Michelle A Calabrese The physics and mechanisms involved in solution-to-gel transitions of aqueous poloxamers with additives is one region of polymer physics that remains difficult to design and control. Tuning transition properties of such solutions remains important for transdermal and transtympanic drug delivery applications. Here, rheometry is utilized alongside differential scanning calorimetry and small-angle X-ray scattering to elucidate mechanisms behind gelation of oil-water emulsions containing Poloxamer 407, methyl laurate, lower molecular weight reverse poloxamers, and ciprofloxacin—for use in noninvasive treatment of otitis media (ear infections). This system can be tuned to gel at body temperature without a significant loss of mechanical properties, leading to greater efficacy of drug delivery systems. The hydrophobic nature of methyl laurate was found to induce gelation in poloxamer concentrations thought to be below the usable range for gelation applications. We show that such solutions allow for increased sensitivity to additives, allowing for more precise modifications. Specifically, modifications to reverse poloxamer molecular weight and poly(ethylene oxide) content are shown to significantly impact gelation properties and antibiotic drug release profiles as compared to neat Poloxamer 407-reverse poloxamer systems. These insights are promising for the continued improvement of noninvasive drug delivery systems for otitis media and other relevant transdermal treatment methods. |
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N00.00146: Can creasing patterns be predicted from a charge crystallization analogy? Tyler A Engstrom, Zoe Bonasera, Florian Sprinzing Prior work has shown that a simple “shear lag” model may be useful as a description of microscopic creases that form in compressed hyperelastic materials, as this model maps to two-dimensional (2D) electrostatics and treats the nonlinearly deformed crease core analogously to a thermodynamically inconsequential vortex core [1]. Here, we extend the shear lag concept to study patterns of macroscopic creases formed under equibiaxial compression [2,3]. Collections of finite-length creases are represented as collections of charged line segments that have pairwise, 2D screened-Coulomb interactions with each other. Random structure searching combined with conjugate gradient relaxation is used to predict ground state crystal structures formed by these line charges as a function of density and screening length. We compare our findings to known equibiaxial creasing patterns, including a square lattice of I-shaped creases with perpendicular nearest neighbors, and a triangular lattice of oriented Y-shaped creases [3]. Given the similarity of these patterns with 2D auxetic patterns, our results may also yield new insights in the latter context. |
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N00.00147: How do fixed pins affect elasticity and rheology of jammed, sheared particles? Xiang Li, Jean Luc Ishimwe, Abir K.M.S. Mahmud, Amin Danesh, Michael J Bolish, Cacey S Bester, Brian Utter, Katharina Vollmayr-Lee, Amy L Graves It has recently been shown that fixing degrees of freedom by adding pinned particles tunes static and dynamic properties of a two-dimensional, soft granular system near jamming. These properties include the jamming threshold, linear elasticity, presence of bond order, and force network topology [1]. |
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N00.00148: Experimental characterization of osmocapillary flattening on gel surfaces with multiscale topogrophy Qihan Liu, Canhui Yang, Jie Zhu When the surface stress tries to deform a polymer gel, it can either deform the polymer network with the solvent, known as elastocapillary deformation or pull the solvent out from the polymer network, known as osmocapillary phase separation. While elastocapillary deformation on gel surfaces has been widely studied, osmocapillary phase separation remains largely a theoretical hypothesis. Here we synthesized non-volatile ionogels cast on sandblasted glass with known surface topography and characterized the swelling-dependent surface topography. Our experiments show that the flattening of the surface features over different length scales can be accurately described by established linear elastocapillary theory when the gel has a low swelling ratio. However, as the gel swells, the elastocapillary theory gradually underestimates the surface flattening. The additional flattening must be explained with an osmocapillary model. This work highlights the importance of osmocapillary phase separation when studying highly swollen gels where existing works often assume that elastocapillary deformation is the only surface deforming mechanism. |
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N00.00149: Non-affine Dynamics of a Sheared Athermal System with Pins Abir K.M.S. Mahmud, Amin Danesh, Jean Luc Ishimwe, Xiang Li, Michael J Bolish, Cacey S Bester, Brian Utter, Amy L Graves, Katharina Vollmayr-Lee We use molecular dynamics simulations to study a two-dimensional athermal, bidisperse system with purely repulsive harmonic interactions. Energy is dissipated via interactions depending on relative velocity. The system additionally includes fixed degrees of freedom in the form of miniscule particles, ‘pins,’ located on a square lattice. Via the motion of rough top and bottom walls composed of frozen particles, we shear the system at a constant rate. During shearing, we adhere to one of two approaches: either maintaining constant pressure or constant packing fraction. For constant pressure shearing, implemented via a top wall which is able to move vertically, we observe a vertical pressure gradient for higher pin densities. |
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N00.00150: Dynamics and rheology of colloidal rod suspensions measured with differential dynamic microscopy laura G Morocho, Nikhil Sonthalia, Ryle R Rel, Esther Yang, Ryan J McGorty Colloidal rod suspensions can form a variety of structures and can form arrested phases at relatively low volume fractions. These properties make them excellent rheological modifiers and useful as model systems to understand complex systems like networks of biopolymer filaments. Both macro- and micro-rheology methods have characterized rod suspensions and gels. Here, we use a relatively new microrheology technique, differential dynamic microscopy (DDM), which combines elements of video microscopy and dynamic light scattering. With DDM we explore how the time scale of density fluctuations, form of the intermediate scattering function, and non-ergodicity parameter scale with both rod volume fraction and aspect ratio. Because DDM works with real space images, we can verify with direct visualization the length scales we pull out from the light-scattering-like analysis framework of DDM. Further, we compare our DDM microrheology with macroscopic bulk rheology in order to make connections between microscale dynamics and bulk mechanical properties, connections which have been built for colloidal gels of spherical particles but which are more challenging to make with anisotropic particles. |
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N00.00151: Yielding Transition in Active Systems Leonardo L Relmucao, Carlos J Villarroel, Gustavo Düring Active matter is a growing area of recent interest due to the wide range of fascinating systems and phenomena which can be studied[1]. In particular, high-density active systems have yet to be studied intensely, despite having many questions and no answers. This work is focused on a dense active system to understand this dynamic controlled by avalanches, unifying quasistatic and dynamic regimes. |
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N00.00152: Early Warning System For Debris Flows Carlo Maino, Saskia Gindraux Debris flows pose significant threats to infrastructure and life. Previous work has established empirical rainfall thresholds for debris flow triggering for single well-studied catchments. However, these approaches suffer from limited transferability to catchments with diverse geology and cannot accommodate varying precipitation patterns driven by a changing climate. In this study we use machine learning (ML) to enhance an existing debris flow early warning system (EWS) for 26 high-impact catchments in the Canton of Valais, Switzerland that triggers alerts when a unique precipitation threshold is exceeded. We extend this methodology to a further 100 catchments in the region with varying geology. Our ML-driven EWS offers a promising avenue to improve debris flow prediction and monitoring, contributing to more effective risk mitigation strategies in a geologically diverse landscape. |
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N00.00153: Tumbling Dynamics of Confined Chiral Active Nematics Zeyang Mou, Rui Zhang Chiral structures and dynamics are prevalent in active and living systems, including chiral biomolecules, helical flagella, and circular motion of microswimmers near a surface. In this study, we investigate the tumbling dynamics of confined chiral active nematics. We demonstrate that the self-spinning of active nematic units can lead to the emergence of novel defect dynamics and spontaneous flow patterns. We further explore the influence of geometry confinement on the dynamics of chiral active nematics, revealing distinct defect dynamics modes and their transitions as the system size and shape vary. Our findings shed light on the complex interplay between activity, confinement geometry, and flow-tumbling parameters in chiral active nematics, providing insights into their dynamical behaviors, and offering opportunities for their applications. |
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N00.00154: Active extensile stress promotes 3D director orientations and flows Mehrana R. Nejad, Julia Mary Yeomans We use numerical simulations and linear stability analysis to study an active nematic layer where the director is allowed to point out of the plane. Our results highlight the difference between extensile and contractile systems. Contractile stress suppresses the flows perpendicular to the layer and favors in-plane orientations of the director. By contrast, extensile stress promotes instabilities that can turn the director out of the plane, leaving behind a population of distinct, in-plane regions that continually elongate and divide. This supports extensile forces as a mechanism for the initial stages of layer formation in living systems, and we show that a planar drop with extensile (contractile) activity grows into three dimensions (remains in two dimensions). The results also explain the propensity of disclination lines in three-dimensional active nematics to be of twist type in extensile or wedge type in contractile materials. |
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N00.00155: Investigating Root Growth in Granular Media with X-ray Computed Tomography Ethan T Mills, Soham Dorle Granular and particulate systems play a vital role in various natural processes, industrial applications, and medicine. Previous research has utilized X-ray computed tomography to analyze soil packing around root growth (Bauer, 2015), however, identifying how root growth changes across different plant species remains to be accomplished. This project focuses on the impact of Arabidopsis root growth as a well investigated model plant on the local packing of granular media. Using daily scans taken over a two week period, the Arabidopsis samples are examined during its primary root growth. We employ X-ray computed tomography to collect scan samples and utilize MATLAB for image analysis. Using image analysis algorithms such as binarization and morphological erosion, we extract grayscale information from voxels to identify particle centroid locations and subsequently segment and isolate the root volume. This data provides valuable insights into the particle system, enabling the tracking of particles and quantifying changes in local packing density with set-voronoi tessellation. This project’s findings serve as a foundation for future research analyzing how root growth impacts the local properties of granular systems, shedding light onto the interactions between root during growth and the granular media it is embedded in. |
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N00.00156: Poster: Molecular Dynamics Simulations of Water in Confined Surfaces. Jose E Nicasio, Shoumik Saha, Dilip Gersappe The freeze-thaw cycles of water in confined media, such as in porous soil is necessary for proper infrastructure development in cold regions experiencing large variations in temperature as a result of climate change. In this project we use the TIP4P/2005 model of water in the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) to try and uncover some poorly understood qualities of confined water. The four site TIP4P/2005 model was chosen over other water models, and even over other four site models, since it gave the most accurate results for density over other models for hexagonal ice. This model includes sites for two hydrogen atoms, one oxygen atom, and a virtual "m" atom between the two hydrogen atoms. Previous literature shows that when liquid-ice boundaries are coexisting with solid surfaces there is a solidification effect on the water molecules even with minimal or no change in temperature or pressure. The Tersoff potential was used to simulate the interactions between the SiO2 wall atoms. We ran simulations of both alpha-quartz crystalline silica as well as annealed amorphous glass silica and compare the ice crystallinity, interface RDF, and atomic density in the Z-direction at varying cooling rates. These results will allow us to understand the fundamental principles of ice formation in confined systems. |
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N00.00157: Manipulating Piezoelectric Phononic Crystals to Create Phononic Devices Alison Root, Tejas Dethe, Andrej Kosmrlj Phononic crystals are periodic metamaterials that interact with elastic waves due to their structure which can be useful for a variety of devices. A soft phononic crystal will buckle under compression, changing its phononic properties and therefore device behavior. This system can be used to make devices with multiple states for sensing applications, or devices that can be tuned to their specific use. To date, much of the research on soft phononic crystals explores externally applied tractions that change the entire structure of the crystal. We propose a soft piezoelectric phononic crystal that can be manipulated in a more targeted fashion with electric fields, which could allow a single phononic crystal to act as different devices depending on the applied electric field. |
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N00.00158: Effects of solvent quality on non-equilibrium self-assembly of polymer fragments during nanogel degradation Zafrin Ferdous Mira, Vaibhav A Palkar, Olga Kuksenok Nanogels find their uses in a broad range of applications, and in many examples these soft particles are placed into solvents of various quality. Controlled degradation can be used to dynamically tailor size, shape, dynamic properties, and aggregation of nanogels in various environments. We focus on hydrogel particles formed by the end-linking of four-arm polyethylene glycol precursors and characterize controlled degradation of these spherical particles in solvents of various qualities. We use Dissipative Particle Dynamics (DPD) approach with modified Segmental Repulsive Potential (mSRP) to overcome unphysical topological crossings of bonded polymer chains. We vary solvent quality in our simulations by choosing corresponding Flory–Huggins interaction parameter capturing interactions between the polymer and solvent. We identify the reverse gel point in various solvents via peak values of the reduced weight average degree of polymerization. We characterize self-assembly of the degraded polymer fragments and remnant nanogels in solvents of various quality. Further, we quantify variation in non-Gaussian character with the extent of degradation reaction depending on solvent quality. |
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N00.00159: DLCA Aggregate Divine Proportion Shape, Fractal Dimension, and the Pascal Triangle. Christopher Sorensen Aggregation is a non-equilibrium process of fundamental importance for dispersed particulate systems. Here I present a restricted hierarchical model of diffusion limited cluster-cluster aggregation (DLCA). The model yields an analytical calculation of the fractal dimensions and self-preserving cluster shapes in two and three spatial dimensions in excellent agreement with those found in nature and simulations. It is shown that the shape is described by a generalization of the Fibonacci series to all spatial dimensions and found in systematic diagonals of the Pascal Triangle. |
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N00.00160: Dynamics of Polyelectrolyte Coacervate Droplets Under External Electric Field ANUSHA VONTEDDU, Aman Agrawal, Alamgir Karim Mixing oppositely charged polyelectrolytes can lead to liquid-liquid phase separation, where polymer-rich droplets (coacervates) are suspended in water, similar to oil-water emulsions. These droplets serve as a model for understanding intracellular phase separation, where similar kinds of phase separation processes lead to the formation of membraneless organelles. In this study, we explored the response of these “artificial” membraneless organelles to electric pulses as an external stimulus. The coacervate droplets were subjected to controlled low dc and ac electric fields. We found that the droplets first assumed an oblate shape and later transitioned into prolate shapes beyond a critical effective field strength. Upon discontinuation of the electric field, the droplets spontaneously returned to their initial spherical configuration. This deformation behavior is attributed to electrohydrodynamic (EHD) flows occurring within the droplets, akin to the phenomena observed in oil droplets in oil-oil suspensions. The equilibrium between electric stress, interfacial tension, and viscous forces orchestrates this deformation process. To our surprise, the extent of deformation in these artificial MLO’s was far beyond what has been observed in oil droplets. |
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N00.00161: Diffusion of concentrated DNA rings undergoing dynamic concatenation Danna Aguilar, Ryan J McGorty, Philip D Neill, Juexin Marfai, Bailey Arnold, Rae Anderson Topoisomerases can cleave, twist, untwist and reconnect ring DNA polymers to enable diverse biological processes including DNA replication and repair, as well as the formation of concatenated structures such as kinetoplasts. When DNA rings are highly overlapping, these topological operations can dramatically alter their diffusion and conformations. Here, we use single-molecule conformational tracking to characterize the non-equilibrium transport and conformational dynamics of highly concentrated DNA rings undergoing dynamic concatenation via the linking and unlinking action of Topoisomerase II. We show that these toplogically-active Olympic rings can exhibit both enhanced and halted diffusivity depending on the Topoisomerase digestion rate and DNA concentration. Future work will build on this bio-inspired platform by incorporating additional enzymes that fragment and ligate DNA for in situ alteration of DNA length. |
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N00.00162: Time-varying diffusion and conformations of topologically-active DNA in composites Michael A Arellano, Juexin Marfai, Ryan J McGorty, Rae M Robertson-Anderson The dynamics and conformations of DNA and other polymers are highly dependent on their topology, especially when the molecules are highly overlapping. DNA exploits the topological conversion from supercoiled to ring to linear forms to allow for processes ranging from replication to repair. Yet, how the dynamics and conformations of DNA molecules evolve during these enzymatically-driven topological operations is largely unknown. Here we use flourescence microscopy and single-molecule conformational tracking to determine the time-evolving center-of-mass motion and conformational size and shape of the DNA undergoing topological conversion from supercoiled and ring architectures to linear chains and fragments. We further investigate the role of dextran crowding on these non-equilibrium properties to shed light on our previous macrorheology results that demonstrated sharp transitions between elastic-like and fluid-like states in DNA-dextran composites. |
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N00.00163: Cholesterol-doped Gear DNA origami: Self-assembly, characterization and lipid membranous interactions Farzin Masshali, Stephen A Sarles In this study, we report the assembly and imaging of Gear-shape DNA Origami (DO) with nine cholesterol-terminated oligonucleotide sequences for anchoring to a lipid membrane, and six fluorescent dye molecules for visualization in confocal microscopy. Following the folding process using an established protocol, transmission electron microscopy (TEM) confirmed the consistent creation of DO structures and established that the inclusion of cholesterol and fluorescent tags does not hinder the assembly of DO structures. To assess DO adsorption on lipid membranes using confocal microscopy, we mixed DO structures, both with and without cholesterol anchors, with giant unilamellar vesicles (GUVs). In the absence of cholesterol anchors, the dye molecules exhibited a uniform distribution of fluorescence in the surrounding solution, whereas GUVs had dim interiors and minimal localized green fluorescence at their outer membrane boundary. In contrast, in the presence of cholesterol-anchored DO there was a sharp increase toward the outer limits of the GUVs. Based on this visual evidence, it can be inferred that the DO, along with their cholesterol anchors, exhibit a significant propensity to adsorb onto the GUVs in substantial quantities. Moreover, it can be observed that the interiors of the GUVs lack illumination, which suggests that DO does not permeate through the membrane. In parallel, calorimetry and electrophysiology techniques are used to quantify cholesterol-doped DO interactions with lipid bilayers. |
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N00.00164: Heat transfer through functionalized carbon nanotubes for photothermal therapy of cancer Delaram Nematollahi, Kieran Mullen, Dimitrios Papavassiliou, Roger Harrison Carbon nanotubes (CNTs) modified with annexin V (AV) protein exhibit the potential to effectively eliminate cancer cells through photothermal therapy. These CNTs possess an affinity for anionic phospholipids found on the surface of cancer cells. Subsequent exposure to near-infrared radiation or radiofrequency fields can induce thermal damage to metastatic cancer cells. |
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N00.00165: Ions Control Assembly of DNA-Functionalized Nanoparticles in Concentrated Electrolytes Roger J Reinertsen, Sumit Kewalramani, Felipe Jimenez-Angeles, Steven J Weigand, Michael J Bedzyk, Monica Olvera De La Cruz Achieving a comprehensive understanding of concentrated electrolytes is challenging due to complex ion-ion and ion-solvent effects. This work utilizes highly charged DNA-functionalized gold nanoparticles to study electrostatic forces in concentrated salt solutions. Small-angle X-ray scattering measurements reveal that divalent cations induce the reversible crystallization of these nanoparticles into face-centered cubic, body-centered cubic, or amorphous structures. The type of structure formed depend on cation type and concentration. Interparticle separations within the assemblies exhibit a non-monotonic dependence on salt concentration; The structures contract with added salt at low salinity, but swell when salt is added at high salinity, where classical theory predicts electrostatic forces to be of negligible range. Observations from wide-angle X-ray scattering and molecular dynamics simulations implicate ion-ion interactions as driving this unexpected swelling at high salt concentration. Changing the solvent mixture to lower the dielectric permittivity increases the electrostatic coupling in the system and enhances these effects. This work demonstrates continuous evolution of interactions between charged objects as salt concentration increases to saturation, providing insight on how ion-ion correlations shape how electrolytes interact with charged materials. |
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N00.00166: How does a DNA motor turn around a corner on DNA origami? Hon Lin Too, Pei Yang, Winna Siti, Zhisong Wang The development of nanosystems capable of executing both translation and rotation bear the potential to catalyse a transformative shift in the landscape of nanorobotics. DNA origami emerges as a promising technology to realize such system, and our recent demonstration of an autonomous, non-bridge burning DNA bipedal motor, capable of executing both translation and rotation on a triangle DNA origami, attests to the feasibility of this approach [1]. Notably, the motor’s motion is inextricably linked to the system’s nanomechanics. To understand how the nanomechanical factors affect the motor foothold search process, additional fluorescence experiments are performed, and oxDNA, a coarse-grained simulation, is used to extract the underlying free energy profile. The simulation captures several non-trivial experimental observations, including a larger decrease in the plus-end fluorescence data at the corner compared to the linear segment, the dependence of the plus-end fluorescence data to the motor length and the foothold positions around the corner. Based on our findings, we provide suggestions to improve the motor walking performance on DNA origami. Our study reveals the intricate nanomechanical effects of motor-origami performance for complex motion, thus contributing to the advancement of DNA nanorobotics. |
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N00.00167: A computational model for studying severing on a Microtubule lattice Pete Miller The microtubule cytoskeleton is shaped by several proteins which regulate all aspects of microtubule growth and shrinkage. Severing proteins are one such microtubule regulator that plays a key role in many cellular processes including mitosis and meiosis, neurodevelopment, and cell migration. How severing proteins work with other microtubule regulating proteins in order to perform these functions is not well understood. Recent in-vitro experiments have shown that free tubulin can repair nanoscale damages of microtubules created by severing proteins. Based on this observation, we study a model that describes microtubule severing as a competition between the processes of damage spreading and tubulin-induced repair. We use a two-dimensional computational model that simulates the removal and reincorporation of tubulin dimers on a microtubule lattice, and quantitatively analyze the resulting severing events. We compute the probability of severing events and the time for severing events to complete as a function of tubulin concentration and compare our results to published results to extract information about severing events. Our preliminary results show similar qualitative behaviors to those seen in published experiments, such as mean severing time scaling with concentration of free tubulin. This model can be extended to examine the effect of tubulin-induced repair on rescues in dynamic microtubules and analyze the size of newly incorporated tubulin. |
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N00.00168: Optimal navigation of interacting active particles on complex landscapes Vishaal Krishnan, Sumit Sinha, L Mahadevan Active many-body systems composed of many interacting degrees of freedom and operating out of equilibrium give rise to non-trivial emergent behaviors across several scales. While non-equilibrium statistical physics provides an effective theoretical framework for developing bottom-up forward models, a corresponding inverse, top-down framework to ascribe function to active many-body systems is lacking. Here we use stochastic optimal control theory to achieve the emergence of functional active matter, in the context of navigation on complex landscapes. We develop the Adjoint-based Path Integral Control (Adjoint-PI Control) algorithm which implements optimal control based on the Feynman-Kac path integral formulation using continuous-time back-propagation. We use numerical experiments of stochastic optimal control of single and many interacting particles in complex external landscapes, and use theory to show that optimal work done is inversely proportional to the length of the time horizon of optimal control. We also study the competition between extrinsic noise strength and the intrinsic energy-scale encoded in the interaction potential. Taken together, our Adjoint-PI Control algorithm provides a foundational framework to control non-equilibrium systems optimally to achieve navigational functionality. |
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N00.00169: Navigation in noisy environments with optimal reorientation Francesco Mori, L Mahadevan In order to move in a straight line, dung beetles switch between egocentric strategies, continuously updating an internal estimate of the location, and geocentric strategies, using landmark cues to correct their trajectory. Applying optimal control theory to a minimal model, I will derive the switching strategy that maximizes the speed. I will discuss the role of environmental, execution, and sensory noise. |
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N00.00170: Heterogeneous Dynamics of Molecular Ions in Grain Boundaries of 1,3-Dimethylimidazolium Hexafluorophosphate Plastic Crystals Hyungshick Park, Bong June Sung Organic ionic plastic crystals (OIPCs) are soft solid electrolytes consisting of charged molecular ions. Although they form crystalline structures, they show high ionic conductivities and plastic-like mechanical properties. To understand their high ionic conductivity even in the crystalline phase, the translational and rotational behaviors of ions have been widely studied. Among them, defects such as point vacancies or grain boundaries are considered to enhance the transport of ions in OIPCs. For example, experimental studies revealed that conductivities and defect concentrations increased together with increasing temperatures. In addition, various experimental and simulation works found that fast and slow diffusing ions coexisted in OIPCs. However, the ion transport mechanism remains elusive at a molecular level partly because it is hard in experiments to systematically control the types of defects. Therefore, we perform molecular dynamics simulations to understand the effect of defects on the dynamics of ions in lithium-doped OIPCs. Two types of defects are considered: 1) point vacancies and 2) grain boundaries (GBs). With point vacancies, the mobilities of all species of ions are facilitated in a heterogeneous fashion. However, the transference number of Li+ decreases with increasing concentrations of point vacancies. In the case of GBs, disordered structures at boundaries are observed. We find that Li+ diffuses along the boundaries and coordinates with more anions than Li+ in bulk crystals without any vacancies. We also find that the time scales of the dynamic heterogeneity of the ions are sensitive to the types of defects. |
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N00.00171: Water Hydrogen Bonding Structures and Dynamics Facilitating CO2 Capture by Amino Acids at the Air-Water Interface Santanu Roy, Benjamin Doughty, Xinyou Ma, Uvinduni I Premadasa, Dengpan Dong, Vyacheslav Bryantsev Amino acids (AA) are showing great promise in direct air capture (DAC) of CO2 at the air-water interface. Water mediates the involved reactions through the solvation of the reactants, intermediates, and products via H-bonding interactions. The local H-bonding structures, their reorganization dynamics during the progress of the reactions, and their reformed structure around the product states are the critical details that set the reaction equilibrium, thermodynamics, and kinetics. In this presentation, we will discuss the utility of reaction rate theory and the semiclassical modeling of the vibrational sum-frequency generation spectroscopy (vSFG) in elucidating the roles of the local solvation structures and reorganization dynamics in the AA-based DAC at the air-water interface. Specifically, the effects of the negative and neutral charge states of the AA and their surface activity on the solvent orientational ordering and coordination number and how these effects are further tailored by the product states of the DAC reactions will be illustrated. In addition, we will provide insight into the solvent rotational dynamics at the interface. Such a molecular-level, detailed understanding of the interfacial structure and dynamics will be critical to enhance the DAC probability. |
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N00.00172: Representing DNA Tranport Phenomena in Cytoskeletal Networks Isaac Blacklow, Dylan P McCuskey, Daisy H Achiriloaie, Jemma Kushen, Jennifer L Ross, Rae M Robertson-Anderson, Janet Y Sheung In the cytoskeleton, motor proteins consume energy from their surroundings to exert forces upon the network’s polymers. This activity complicates transport dynamics across the network, often leading to anomalous diffusion distinct from normal Brownian motion. Many studies have characterized such transport with ensemble-averaged mean-squared displacement (MSD), relating MSD to lag time by MSD ~ Δtα, where α < 1 and α > 1 indicate subdiffusion and superdiffusion, respectively. Here, we use single-particle tracking to examine the transport of fluorescent microspheres, circular DNA, and linear DNA across cytoskeletal networks of microtubules and kinesin. However, while traditional ensemble MSDs give us a rudimentary understanding of particle movement, we notice unprecedented multi-phasic behavior that compels us to seek an alternative method of data representation. Disaggregating the MSDs reveals distinct populations of particles that ensemble MSDs average together. By examining videos with split spatial heterogeneity, we color-code the particle MSDs to conclude that the differences between these populations are related to diffusion dynamics. To better present these dynamics, we plot density distributions of the anomalous scaling exponents (α) for each particle MSD at a given lag time. Such distributions present intriguing transport dynamics that the traditional ensemble MSDs do not suffice to encapsulate, and our results have implications for many biological and industrial processes. |
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N00.00173: Improved quantification of colloidal dynamics with machine learning and simulations Dylan Gage, Gildardo Martinez, Justin Siu, Emma Kao, Juan Carlos Avila, Ruilin You, Ryan J McGorty Techniques like dynamic light scattering and particle tracking are often used to quantify the dynamics or rheological properties of soft matter systems or complex fluids. A more recent technique that combines features of optical microscopy and light scattering is differential dynamic microscopy (DDM). This technique utilizes microscopy-acquired real-space videos to calculate correlation functions using a framework similar to light scattering methods. DDM has been used to measure the diffusion of colloids or nanoparticles, the dynamics of gels, and the fluctuations of cytoskeleton networks driven by molecular motors. In most of these cases, 1000s of image frames are necessary to analyze the dynamics accurately with DDM. To overcome the need to acquire large amounts of imaging data, we use a convolutional neural network (CNN) to denoise DDM data. With this machine learning approach to DDM, we can accurately quantify motion using imaging data acquired in significantly less time. Training of the convolutional neural network can involve using vast amounts of experimentally acquired data across a range of conditions. More efficiently, we can train the CNN using simulated video microscopy data. We show that models trained on simulations work well on experimental data. With this approach, we quantify dynamics that are quickly evolving in time and demonstrate how high-throughput measurements of rheological properties can be performed. |
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N00.00174: High Throughput Screening towards the Rational Design of Active Matter Rae M Robertson-Anderson, Jonathan A Michel, Qiaopeng Chen, Karthik Reddy Peddireddy, Michael J Rust, Jennifer L Ross, Moumita Das, Ryan J McGorty, Megan T Valentine We introduce sample-agnostic techniques to screen microscopy data from active matter systems for three properties of interest: ability to transmit force, significant contractile motion, and lifetime of structures. Screening of large data sets can be laborious, and may slow optimization of experimental protocols, and so means of rapidly identifying promising specimens are highly desirable. We have developed computational tools to apply efficient heuristics to series of images to identify samples which may have a desired trait. Because all techniques are designed to be sample agnostic, all that is required is a set of image intensity data at regular time intervals. We thus anticipate our software will be of interest to the broader soft matter community. We assess the possibility of force transmission by testing for correlation of velocity directions over large distances, a necessary, though not sufficient condition. We have found a decreasing correlator corresponds with the breakup of anactomyosin network into small clusters. To check for contractility, we look for a decreasing characteristic decay length in image intensity autocorrelations. Finally, we quantify the persistence of the spatial structure of a sample by computing the largest void size in the intensity field. |
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N00.00175: Defect Dynamics in Colloidal Crystals Assembled using Time-Varying Magnetic Fields Sibani Lisa Biswal, Dana Lobmeyer Time-varying magnetic fields can be used to assemble colloidal crystals. Specifically, rotating magnetic fields supply a continuous energy input that allows for dynamic changes in the crystal microstructure as a result of grain boundary rearrangements. Interfacial shear acts as a mechanism by which voids within the crystal initially act as a sink to dissipate defects, but can also act as sources of grain boundaries due to local energy and microstructure arrangments. In many cased, local rotation induced by shear at the void produces rapid orientational changes before forming a distinct grain boundary that translates through the bulk of the colloidal crystal. This grain boundary propagation either creates grain boundaries that persist or generates a temporary grain boundary that ultimately merges with an existing one, thereby removing a grain and its grain boundary in the process. In both cases, |
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N00.00176: Aggregation and Cluster Composition in Latex-Pigment Mixtures: A Molecular Simulation Study Ashley R Knoerdel, John K Riley, Steven G Arturo, Antonia Statt Aggregation and stability of colloidal suspensions is important in many applications, ranging from food products to paints. Composite and aggregate formation in high-end latex-based coatings is not well understood on the fundamental level. Using molecular dynamics simulations, we aim to provide insights into cluster formation in a mixed system of latex and pigment particles. Understanding this system is challenging, as the system contains not only latex and pigment particles, which are comprised of multiple layers, but dispersants and other additives that affect the cross and self-interactions of all components. We will provide insights to this system to understand how the interactions between different components will affect the aggregation of clusters, and hence the final mechanical and optical properties of the formed paint films. By varying the amount of latex compared to pigment in the system, the total volume fraction of latex and pigment, and the strength of the cross- and self-interactions we investigate cluster size, shape, composition, and the system's propensity to aggregate. |
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N00.00177: Dynamics of C-Shaped Particles Moving Through an Obstacle Field Ollie Yakimow, Scott V Franklin We experimentally study the motion of C-shaped superellipse sector particles (SeSPs) as they fall through an obstacle array. SeSPs are two-dimensional particles parameterized by corner sharpness, aspect ratio, and opening angle; these parameters are sufficient to represent a large variety of shapes, including discs, rods, and concave and convex particles. Our obstacle array consists of circular pegs (cm-regime) placed with rhombic symmetry and a spacing slightly larger than the SeSP diameter. We use particle tracking to map SeSP translational and rotational motion, investigating how peg-particle interactions change the particle trajectory of a single particle moving through the array. Because of a concave particle shape, single particles can be arrested by a single peg, behavior not seen in circular or elliptical particles. From there, we move on to study collective motions of multiple particles, investigating cooperative motions that result in clogging and jamming, both locally in an isolated region of space and globally, arresting the bulk flow. |
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N00.00178: Impact of Particle Morphology, Preparation Method, and Confinement on the Angle of Repose for Granular Materials Ethan Zimmerman, Donovan Corbin, Jonah Goolsby, Klebert B Feitosa Understanding and predicting avalanches, mudslides, and other similar granular flows has many applications in geophysics, civil engineering, and mining. The angle of repose is an important parameter characterizing particle flow in granular piles. We investigate how the angle of repose depends the particle's aspect ratio, preparation method, and confinement. For piles made of prolate particles of aspect ratios ranging from 2.5 to 6 flowing down from a channel, the angle of repose decreases with increasing aspect ratio. By contrast, numerical studies report an opposite trend, although for particles within a smaller and narrower range of aspect ratios then the ones we tested. Interestingly, when the pile is formed by rotating the container, the angle of repose increases with aspect ratio, suggesting that pre-existing entanglement between longer particles helps sustain steeper slopes. We also observed that pile confinement has a relatively smaller impact on the angle of repose, with greater confinement making the angle of repose generally steeper regardless of aspect ratio. |
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N00.00179: Influence of surfactant choice on stratification of freestanding micellar films Yash Vidyasagar, Chenxian Xu, Chrystian Ochoa, Vivek Sharma, Sehar Ahmed Ultrathin foam films containing supramolecular structures like micelles in bulk, and adsorbed surfactant at the liquid-air interface, undergo drainage via stratification. At a fixed surfactant concentration, the stepwise decrease in average film thickness of a stratifying micellar film yields a characteristic step-size that also describes the quantized thickness difference between coexisting thick-thin flat regions. It is well-established that step-size is inversely proportional to the cubic root of SDS concentration, and cannot be estimated by adding micelle size to Debye length, as the latter is inversely proportional to the square root of SDS concentration. Recently we contrasted the step-size obtained from the analysis of nanoscopic thickness variations and transitions in stratifying SDS micellar foam films using Interferometry Digital Imaging Optical Microscopy (IDIOM) protocols (that we developed) with the intermicellar distance obtained using small-angle X-ray scattering. We found that step-size equals to intermicellar distance obtained using scattering from bulk solutions, and stratification driven by the confinement-induced layering of micelles within the liquid-air interfaces of a foam film provides a sensitive probe of non-DLVO oscillatory forces and micellar interactions. In this contribution, we examine the concentration dependency of step-size and layer number for anionic surfactants, including SDS, SDBS, and NaN, and contrast these with observations for nonionic surfactants. |
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N00.00180: Influence of Surfactants, Polymers and Proteins on Foam Film Drainage Chenxian Xu, Carina Martínez Narváez, Lena Hassan, Patrycja Kotwis, Vivek Sharma Foams can be described as colloidal dispersions containing large gas cells separated by thin liquid films, whose junctions are called Plateau borders. Drainage of individual ultrathin foam films (thickness < 100 nm) into Plateau borders is governed by the interplay of capillarity, disjoining pressure, viscosity, and interfacial rheology. It is well-established that confinement-induced structuring and layering of supramolecular structures like micelles, liquid crystals, colloidal particles, or polyelectrolytes within foam films results in drainage via stratification. Only few examples show the possibility of stratification in foam films containing polymers or proteins. In this contribution, we visualize and analyze drainage in foam formulated with surfactants, proteins, polymers and their mixtures, and describe the specific connection to foam stability and applications in diverse areas in foods, cosmetics, environmental remediation, oil recovery, and healthcare. |
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N00.00181: Poster: Coarse-Grained Modeling of Ionic Liquid Crystals Logan M Hennes, Marvin Diaz Segura, Jennifer L Schaefer, Jonathan K Whitmer Solid-state electrolytes are hypothesized to be a safe alternative to liquid electrolytes currently used in lithium-ion batteries, which can simultaneously meet the growing consumer demand for energy-storage. The best mechanisms for incorporating the solid state are a matter of significant research. Polymer based electrolytes have received significant attention for their mechanical stability, but often exhibit low conductivities which limits their technological impact. Partially ordered ionic liquid crystals could improve the ionic conductivity by allowing the dissociated ions to migrate within charge-rich layered domains. This work focuses on developing a physics-based coarse-grained model of ionic liquid crystals as a means to assess this hypothesis and the feasibility of these materials for energy storage. In particular, we will explore the limits of phase behavior, influence of the phase on conductivity, and the influence of added solvent in facilitating ion motion. |
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N00.00182: Phase transitions and dynamcis in ionic liquid crystals confined in nanopores Hiroki Nobori, Daisuke Fujimoto, Jun Yoshioka, Takashi Konishi, Ken Taguchi, Koji Fukao We investigated the phase transition behavior of ionic liquid crystals, 1-methyl-3-alkylimidazolium tetrafluoroborate, [Cn mim]BF4, confined in cylindrical nanopores using differential scanning calorimetry, X-ray scattering, and dielectric relaxation spectroscopy. For n=12 and 10, the isotropic liquid phase changes to the smectic phase and then to a metastable phase for the cooling process. During the subsequent heating process, the metastable phase changes to the isotropic phase via crystalline phases. The transition temperatures for this ionic liquid confined in nanopores decrease linearly with the increase in the inverse of the pore diameter, except for the transitions between the smectic and isotropic phases. In the metastable phase, the relaxation rate of theα-process shows the Vogel-Fulcher-Tammann type of temperature dependence for some temperature ranges. The glass transition temperature evaluated from the dynamics of the α-process decreases with the decrease in the pore diameter and increases with the increase in the carbon number n. The confinement effect on the chain dynamics can clearly be observed for this ionic liquid crystal. For n=10, the melting temperature of the crystalline phase is slightly higher than that of the smectic phase for the bulk, while that of the smectic phase increases more significantly with the decrease in pore diameter than that of the crystalline phase. This suggests that the smectic phase can be a thermodynamically stable phase due to the confinement effect. |
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N00.00183: Study of waveguides based in liquid crystals interfaces Guillermo Reyes, Juan Adrian Reyes, Panayotis Panayotaros We study an air-glass interface with an additional thin bilayer consisting of a cholesteric liquid crystal doped with silver nanospheres, and a silver thin film. |
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N00.00184: Lipid Membrane Interactions with Polymer-Grafted Nanoparticles Jordan Darling, Mohamed Laradji, Abash Sharma, yu zhu, Eric J Spangler Many recent studies have been performed to investigate the interaction between nanoparticles with lipid membranes. In most of these studies, the nanoparticles interact directly with the membranes through their surfaces. The fluidity and elasticity of a lipid membrane allow it to deform, such as it conforms to the surface of an adhering nanoparticle to an extent determined by the competition between the adhesive interaction and the membrane's curvature energy. An interesting result of these deformations is that they can be long-ranged and, thereby, lead to membrane-curvature-mediated interaction between adhering nanoparticles. This can result in the aggregation of the nanoparticles on the membrane. Furthermore, high adhesive interaction leads to the endocytosis of the nanoparticles. In some applications, both endocytosis and membrane-induced aggregation of nanoparticles are not desirable. Here, we will show that surface modification of the nanoparticles by partially grafting their surfaces with hydrophilic polymers prevents both their endocytosis and aggregation. Systematic simulations, using a coarse-grained implicit-solvent model, with varying values of the grafting density, length of the polymer chains, and strength of the adhesive interaction, are performed to determine the optimal set of parameters to suppress endocytosis and aggregation of polymer-grafted spherical nanoparticles on lipid vesicles. |
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N00.00185: Transfer Kinetics of Cargo Items among Mobile Nanocarriers Md Faruk Hossain Micelles, liposomes, microgels, dendrimers, and nanoparticles represent nanocarriers that deliver cargo items–often drug molecules–to a target. We calculate the kinetics of collision-mediated transfer of cargo items within ensembles of chemically distinct mobile nanocarriers in the Gaussian regime. To this end, the relevant rate equations for collision-mediated transfer of cargo items are expressed in the continuum limit as a set of Fokker-Planck equations and solved analytically. The solutions fully describe the time evolution of an arbitrary initial distribution of the cargo items among the nanocarriers toward equilibrium. |
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N00.00186: Analyzing Depolarized Dynamic Light Scattering by Solutions of Elongated Particles Kiril A Streletzky, Geofrey M Nyabere, Nehal Nupnar, Michael A Hore Using Depolarized Dynamic Light Scattering (DDLS) to study structure and dynamics of geometrically anisotropic nanoparticles in solution requires good quality intensity correlation data collected at a range of angles and concentrations and careful consideration of appropriate assumptions and various geometrical models. This project is aimed to analyze the effectiveness of different approaches to DDLS data analysis and use of appropriate assumptions for the solutions of geometrically anisotropic nanoparticles. The focus was on three geometrical models: de la Torre's straight cylinder, Perrin's prolate ellipsoid, and Martchenko et. al.’s spherocylinder and on two different approaches to data analysis. In the first approach, the angular dependence of relaxation decay rates of measured intensity correlation functions was used to obtain translational and rotational diffusion coefficients of the system that were then used for finding the geometrical anisotropy of the particles for a given model. In the second approach, a single scattering angle correlation functions were analyzed, and their decay rates used to solve for particle dimensions using the same geometrical models. Both approaches and the three geometrical models were tested on the DDLS data on aqueous solutions of gold nanorods (AuNRs). The conclusions on the applicability and limitations of each approach for various geometrical models will be presented. |
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N00.00187: Liposomes-Induced Nanostar Self-Assemblies of Spherical Nanoparticles yu zhu, Abash Sharma, Eric J Spangler, Mohamed Laradji Using molecular dynamics of a coarse-grained implicit-solvent model, we show that liposomes can self-assemble spherical nanoparticles, adhering to the liposomes' inner surface, into novel quasi-two-dimensional star-like nanoclusters. The geometric details of these nanostar assemblies depend on the number of adhering nanoparticles. The simulations indicate that for weak adhesion strength, the spatial correlations of the adhering nanoparticles are weak. However, over a wide range of intermediate values of the adhesion strength, the increased nanoparticles' degree of wrapping leads them to deform the spherical vesicle from a three-dimensional geometry to a flattened two-dimensional star-like geometry, in which the nanoparticles' positions are highly correlated. At high adhesion strength, the nanoparticles are exocytosed. Interestingly, several long-lived transient states, depending on the number of nanoparticles, including tetrahedra, triangular prisms, octahedra, etc., form during the transformation of the nanoclusters' geometries from three to two dimensions. The stability of the nanoclusters is inferred from free energy calculations based on the Helfrich Hamiltonian. These novel two-dimensional nanoassemblies should have various applications. For example, they can be used as bio-friendly gears in molecular machines. |
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N00.00188: Gravity and Patch Coverage Impact on Patchy Colloidal Gel Collapse Umesh V Dhumal, Roseanna N Zia Patchy colloidal gels with strong directional interactions exhibit a rich range of phase behavior and serve as a robust model system for protein and other gels. Equilibrium and non-equilibrium states (e.g., gels and glasses) are influenced by the number and size of patches on particle surfaces. While the morphology and compactness of these systems are predominantly determined by the strength of inter-particle potential, gravity plays a role in shaping the number and size of clusters. Moreover, the extent of patch coverage dictates when gravitational effects come into play. Previous investigations into the collapse of colloidal gels under gravity have identified three distinct phases: slow compaction, transition to rapid collapse, and long-term densification, indicating that the primary mechanism driving gel collapse is non-equilibrium phase separation. In this work, we examine how the interplay between gravitational force and patch coverage affects the collapse of colloidal gels. We characterize microscopic changes in the gel structure by tracking particle positions, coordination numbers, and bond dynamics. Osmotic pressure helps distinguish between phase-separation-driven condensation and compaction due to gravity. Besides monitoring the gravitational collapse, we construct a comprehensive phase diagram encompassing equilibrium and non-equilibrium phases. |
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N00.00189: Equilibrium structured liquids: Self-assembled fluid structures stabilized by nanoparticles Anthony Raykh, Alex McGlasson, David Hoagland, Thomas P Russell The gross liquid-liquid interfacial morphology of structured liquids can be altered in response to a bulk external stimulus. We previously created structured liquid droplets by jamming nanoparticles at their liquid-liquid interfaces, but these nonequilibrium systems were unstable to emulsification. To achieve better morphological stability, i.e., to avoid emulsification, we now have fabricated structured liquids with magnetic nanoparticles, finding unexpected and stable morphologies that quickly reassembled when broken apart. The stable morphologies were not always those of minimal interfacial areas. This setup provides a novel platform for studying the packing and dynamics of nanoparticles at interfaces, as well as for building thermodynamically stable liquid structures. |
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N00.00190: Stress-stress Correlations in Soft Particulate Gels H. A Vinutha, Albert Countryman, Fabiola Diaz Ruiz, Xiaoming Mao, Emanuela Del Gado, Bulbul Chakraborty We investigate the spatial correlations of microscopic stresses in soft particulate gels using 2D and 3D numerical simulations. We use a recently developed theoretical framework predicting the analytical form of stress-stress correlations in amorphous assemblies of athermal grains that acquire rigidity under an external load. These correlations exhibit a pinch-point singularity in Fourier space. This leads to long-range correlations and strong anisotropy in real space, which are at the origin of force-chains in granular solids. Our analysis of the model particulate gels at low particle volume fractions demonstrates that stress-stress correlations in these soft materials have characteristics very similar to those in granular solids and can be used to identify force chains. We show that the stress-stress correlations intensity patterns reflect changes in shear moduli and network topology, due to the |
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N00.00191: Assembly by Solvent Evaporation: Free Energy, Role of Solvent and the Equilibrium State Alexander Upah, Alex Travesset, Leandro Missoni, Mario Tagliazucchi Many ordered nanostructure assemblies with crystalline and quasi-crystalline order have been experimentally realized via solvent evaporation, where the presumably equilibrium state is free of solvent. Understanding the equilibrium structure and thermodynamic stability of these realized nanoparticle (NP) systems requires precise free energy and internal energy calculations. In this talk, I will systematically discuss two aspects of nanoparticle assembly by solvent evaporation. First, I will discuss the factors that control the accuracy calculations via molecular dynamics simulations for free energies in the dry state to 1 kBT precision, such as timestep, thermostat type, drag coefficient, and the parameter of the harmonic bias potential, ultimately providing optimal parameter values and precise calculations of free energies and internal energies. Second, I will discuss the process of solvent evaporation in a superlattice and compare the results against the predictions from a mean field molecular theory (MOLT). Application of both MD and MOLT computations allows for efficient calculation of various thermodynamic and dynamical quantities of a given nanoparticle system, allowing a detailed understanding of nanoparticle assembly via solvent evaporation. |
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N00.00192: A density-independent reentrant jamming transition in confluent monolayers of synthetic cell-mimics PRAGYA ARORA, Souvik Sadhukhan, Saroj K Nandi, Dapeng(Max) Bi, Ajay K Sood, Rajesh Ganapathy In assemblies of rigid particles, increasing the packing fraction can drive the transition from a fluid-like to a jammed solid-like state. However, in crucial biological processes such as wound healing, this dynamic arrest occurs while maintaining confluence, with the packing fraction remaining unity. This remarkable feature of cell monolayers is possible because cells are deformable objects and the constraining effects of high density are easier to overcome via changes in the cell shape. Furthermore, recent experimental and theoretical studies suggest that cell shape fluctuations, discarded as experimental noise until now, correlate with dynamics. In this study, we design and assemble a monolayer of synthetic cell-mimics. Our investigation revealed a density-independent re-entrant jamming transition driven by the shape of cells, on increasing activity. We observe that cell shape variability in our synthetic system mimics those seen in confluent cell monolayers and are mutually constrained and follow the same universal scaling as that observed in confluent epithelia. However, we have identified a deviation from this scaling behavior for the fast-moving cells, which exhibit suppressed shape variability. Our simulations attribute this reduced shape variability to a temporary confinement effect imposed by slower neighboring cells. Our synthetic model system allows precise manipulation of both activity and deformability and facilitates a direct comparison with theoretical and numerical predictions. |
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N00.00193: Emergent properties of constrained active particle chains Kimberly Bowal, Kyungmin Son, L Mahadevan, Ho-Young Kim Active collective systems are composed of many individuals that possess the ability to cooperatively change their group shape and motion. Synthetic systems with these properties can be useful for addressing functional applications or elucidating guiding principles in natural collectives. The design and use of these robotic systems requires understanding of the ways that the constraints of individuals affect the functional performance of the collective. We investigate how simple steric interaction rules between active individuals produce a versatile active system with promising functionality, by studying a chain of forward-propelled particles that can be defined by its internal geometric interaction constraints. A variety of emergent properties arise from this dynamic system, including directed movement, interactions with obstacles, and transport of loads. Modifying the geometric constraints between the active chain components provides a rich range of these observed behaviours. The resulting low- and high-level emergent properties are evaluated using an agent-based model, with a focus on understanding how the geometric constraints and relationships between interacting individuals control the collective behaviours. |
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N00.00194: Stringiness and rheology of saliva substitutes Karim Al Zahabi, Lena Hassan, Ramiro Maldonado, Michael Boehm, Stefan Baier, Vivek Sharma Saliva substitutes are man-made formulations commonly used in medicine, food, and pharmaceutical research to emulate the biochemical, tribological, and rheological properties of human saliva. Natural saliva possesses stringiness or spinnbarkeit, governed by extensional rheology response which cannot be evaluated or anticipated from the knowledge of shear rheology response. Even though extensional flows involving saliva are commonly encountered in situations such as swallowing, coughing, sneezing, licking, drooling, and blowing spit bubbles, rheological evaluations of saliva and its substitutes in most studies rely on shear viscosity alone. In this contribution, we provide a comprehensive examination of the shear and extensional rheology of twelve commercially available saliva substitutes and dry mouth treatments using rate-dependent torsional rheometry and dripping-onto-substrate (DoS) protocols, and evaluate their properties based on pioneering studies of saliva's viscoelasticity. Despite the majority of these formulations being marketed as having enhanced rheology, only three displayed measurable viscoelasticity and strain hardening, and did so at viscosities significantly higher than that of saliva. |
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N00.00195: Scaling description of frictionless dense suspensions under inhomogeneous flow. Bhanu Prasad Bhowmik, Christopher Ness Predicting the rheology of dense suspensions under inhomogeneous flow is crucial in many industrial and geophysical applications, yet the conventional 'μ-J' framework is limited to homogeneous conditions in which the shear rate and solids fraction are spatially invariant. To address this shortcoming, we use particle-based simulations of frictionless dense suspensions to derive new constitutive laws that unify the rheological response under both homogeneous and inhomogeneous conditions. By defining a new dimensionless number associated with particle velocity fluctuations and combining it with the viscous number, the macroscopic friction and the solids fraction, we obtain scaling relations that collapse data from homogeneous and inhomogeneous simulations. The relations allow prediction of the steady state velocity, stress and volume fraction fields using only knowledge of the applied driving force. |
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N00.00196: Thermodynamic description of the stress overshoot in sheared soft particle glasses Nazanin Sadeghi, Hrishikesh M Pable, Fardin Khabaz Particle dynamics simulations are used to study the start-up flow of jammed soft particle suspensions in shear flow from a thermodynamic perspective. This thermodynamic framework is established using the concept of the two-body excess entropy extracted from the pair distribution function and elastic energy of the particles. Results show that the evolution of the elastic energy in the system closely mimics the stress-strain behavior at different shear rates. Furthermore, the transient excess entropy of the suspensions at all volume fractions shows general behavior: the excess entropy at high shear rates increases as a function of the strain, shows a mild overshoot, and attains a steady state. On the other hand, it is nearly constant at shear rates close to the dynamic yield stress. Using the transient elastic energy and excess entropy, an effective temperature is defined to establish a relationship between thermodynamics and the static yield stress data. The magnitude of this effective temperature shows a direct relationship with the peak stress and shows universal behavior for suspensions with different volume fractions. |
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N00.00197: Kitchen Pot Thickens, Drop by Drop Somayeh Sepahvand, Louie Edano, Nadia Nikolova, Mohammad Shamsheer, Karthika Suresh, Vivek Sharma Many food formulations contain sugars and polysaccharides as thickeners that influence flow behavior, stability, processability, texture, and mouthfeel. Interfacial and rheological properties of key ingredients including polysaccharides influence production and processing of various foods, as well as the consumer perception and bioprocessing that begin withe every bite. Typically, chefs, formulators and regular cooks in kitchens judge stickiness, stringiness, spinnability, ropiness, and flowability by dripping a sauce or a mixture from a ladle, stretching a liquid bridge between finger and thumb, or by dispensing from a nozzle/bottle onto a substrate. Stream-wise velocity gradients associated with extensional flows spontaneously arise during these operations associated with dripping, dispensing or stretching liquid bridges. In spite of great advances in quantitative characterization of shear rheology response, elucidating, measuring and harnessing the extensional rheology, there remain well-known challenges associated with robust, reliable and affordable measurement of extensional rheology response. In this contribution, we present a range of experiments that emulate the kitchen flows and survey the influence of typical thickeners by quantitative studies relying on visualization and analysis of pinching flows encountered in dripping, dispensing, and stretched liquid bridges. |
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N00.00198: Impact and energy absorption with sticky crumpled matter Wathsala M Amadoru Jayawardana, Andrew B Croll Sticky crumpled matter is a promising material system for the creation of protective layers, such as those used in helmets, body armor, and vehicles. They are lightweight, stiff, and can store significant energy through interfacial phenomena such as adhesion. In this study, we investigate the energy absorption capabilities of sticky crumpled matter using a simple ball drop experiment with high-speed photography and force measurement. We find that the interplay of sheet adhesion, sheet thickness, and sheet modulus plays a key role in the energy absorption process. Our results suggest that sticky crumpled matter can be a viable alternative to current protective structures and materials and have the potential to be used in a wide range of applications. |
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N00.00199: STATISTICAL AND NONLINEAR PHYSICS
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N00.00200: Unveiling Roadway Network Safety: Application of Statistical Physics to Crowdsourced Velocity Data Meshkat Botshekan, Franz-Josef Ulm The incessant rise in vehicle-caused fatality rates worldwide motivates us to investigate the near-miss collision risk in traffic flow using attributes of statistical physics. We find that the statistics of accident precursors can be mapped onto a phase diagram that elevates observables, such as traffic density and velocity fluctuations, to predictive metrics of accident risk. To this end, we derive the near-miss collision risk from the velocity state transition matrix, considering the excessive deceleration of particles in steady-state traffic flow. We probe our model against actual collision data using both simulation-based and crowdsourced vehicle velocity data. We show that an intrinsic near-miss collision risk exists, is confined to congested flow, and predicts the highest likelihood of actual collisions. This risk decreases with increasing randomness in driver behavior—a feature it shares with many other many-body systems with long-range correlations triggered by randomness, e.g., random agents moderating price fluctuations in financial markets. We further advance our discussion by applying the methodology to large-scale crowdsourced velocity data across various states in the United States. Specifically, focusing on a network's ability to sustain functionality and connectivity amid potential disruptions, we examine the reliability and resiliency of roadway networks at the state scale by upscaling path-related attributes. |
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N00.00201: Signature of out-of-equilibrium dynamics in a partially observed system jean-baptiste masson, christian L vestergaard, alexander serov
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N00.00202: Topological phase locking in dissipatively-coupled noise-activated processes Michalis Chatzittofi, Ramin Golestanian, Jaime Agudo-Canalejo We study a minimal model of two non-identical noise-activated oscillators that interact with each |
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N00.00203: Nonequilibrium Thermodynamics on Ratchets in Brownian Computing in terms of First Passage Time and Entropy Production Sho Nakade, Yasuhiro Utsumi, Teijiro Isokawa, Ferdinand Peper Brownian circuits are delay-insensitive circuits that can effectively utilize thermal fluctuations of Brownian particles [1]. In these circuits, thermal noise serves as a resource to drive signals, offering the potential for significantly reduced energy consumption compared to conventional computers. However, the thermodynamic lower limit of the energy consumption on this circuit remains unclear because of its non-equilibrium calculation processes which use the diffusion of Brownian motion. In this study, we aim to elucidate the thermodynamic cost of ratchets, one of the key components of Brownian circuits. Ratchets rectify fluctuating particles and give them a unidirectional motion. They play a critical role not only in increasing computational speed but also in terminating computation and erasing information. We consider a one-dimensional random walk model and derive the first passage time of a Brownian particle for each ratchet performance. We show that ratchets exhibit varying first passage times depending on their positioning even for the same ratchet performance. Our presentation provides a detailed account of the performance and positional dependencies of ratchets in terms of entropy production. |
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N00.00204: Increasing free-energy gain on co-evolving qubit networks Unnati Akhouri An interesting class of physical systems, including those associated with life, can hold thermalization at bay and perpetuate states of high free energy compared to a local environment. The subsystems evolve in a way that depends on and restricts the dynamics of the neighboring subsystems and the environment. How does the network of interactions between subsystems assist in perpetuating states of high free energy? |
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N00.00205: Constraint on local definitions of quantum internal energy Frederico B Brito, Luis Rodrigo Torres Neves Recent advances in quantum thermodynamics have been focusing on ever more elementary systems of interest, approaching the limit of a single qubit, with correlations, strong coupling and far-from-equilibrium environments coming into play. Under such scenarios, it is clear that fundamental physical quantities must be revisited. Here, we question whether a universal definition of internal energy for open quantum systems can be devised, setting limits on its possible properties. We argue that, for such a definition to be regarded as local, it should be determined by using only local resources, i.e., the open system's reduced density operator $varrho$ and its time derivatives. The simplest construction, then, would be a functional $U(ρ, dot{varrho})$. We adopt the minimalist implementation of a bipartite quantum universe, namely two qubits in a pure joint state, and show that the functional relationship cannot be that simple if it is to generally recover the well-established internal energy of the universe. No further hypothesis or approximation scheme was assumed. |
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N00.00206: Entropy flow in CR-gate Radhika Hemant Joshi, Mohammad H Ansari, Alwin van Steensel Cross-resonance gate is a two-qubit gate performed by driving one of the qubits (control) at the frequency of the other (target) [1]. We study such a sytem in the presence of external reservoirs [2]. In our model each qubit is coupled to a reservoir, where each reservoir is at a different temperature. The qubits also interact with each other and hence evolve to become entangled [3]. We calculate the entropy flow through the reservoirs and see how it is affected by the entanglement between the qubits [4]. Obtaining such a relation makes it feasible to control the entropy flow within a system by controlling the entanglement between qubits. |
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N00.00207: ABSTRACT WITHDRAWN
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N00.00208: Towards a random matrix theory of non-Markovian open quantum systems Lucas Sá, António F Oliveira, João Costa, Pedro Ribeiro The evolution of open quantum systems depends on how they interact with their environment, which is, unfortunately, notoriously hard to model. One commonly used approximation is to consider memoryless environments (the so-called Markovian approximation), greatly simplifying the analysis. Assuming the system to be complex, and thus employing random matrix techniques, we show that universal properties emerge in random Markovian dynamics. However, such an approach fails in several situations, such as transport setups and noisy intermediate-scale quantum computers. Therefore, we determine universal signatures of non-Markovian dissipative systems by applying random matrix methods to study their spectral and steady-state properties. We focus on quadratic systems where an exact solution can be found and identify how the departure from Markovianity modifies the universal properties of the ergodic regimes identified in the Markovian case. In particular, we establish how the system-bath coupling and the thermodynamic features of the environment affect spectral and steady-state properties. |
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N00.00209: Effects of Parity-Deformed Heisenberg Algebra in the Dicke Model Saravana Prakash Thirumuruganandham, Edgar A Gómez, Daniel Salazar Camacho, Edward García Daniel Salazar camacho1, Edward García1, Edgar A. Gómez1, Saravana Prakash Thirumuruganandham2 1Programa de Física, Universidad del Quindío, Quindío, Colombia
2Centro de Investigación de Ciencias Humanas y de la Educación (CICHE), Universidad Indoamérica, Ambato 180103, Ecuador
In scientific literature, the Dicke model consists of N two-level systems coupled to an optical nanocavity and exhibits fascinating phenomena such as quantum phase transition. In this system, the system can transition from a normal state to a superradiant state depending on the coupling strength between radiation and matter. This work presents a theoretical and computational study of a Dicke-type system, taking into account a parity deformation in the algebraic structure of the confined radiation mode of the nanocavity. In particular, the effect of parity deformation on different quantum phases is investigated by calculating observables of the system as a function of the coupling intensity between radiation and matter, subsystem entropy, Wigner functions, and Fock distributions for various deformation parameter values. Additionally, calculations of subsystem entropy as a function of the number of two-level systems are presented. It is found that parity deformation can induce significant changes in the Wigner functions and Fock states of the system. |
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N00.00210: Level statistics of real eigenvalues in non-Hermitian systems Zhenyu Xiao, Kohei Kawabata, Xunlong Luo, Tomi Ohtsuki, Ryuichi Shindou Symmetries associated with complex conjugation and Hermitian conjugation, such as time-reversal symmetry and pseudo-Hermiticity, have a great impact on the eigenvalue spectra of non-Hermitian random matrices. Here, we show that time-reversal symmetry and pseudo-Hermiticity lead to universal level statistics of non-Hermitian random matrices on and around the real axis. From the extensive numerical calculations of large random matrices, we obtain the five universal level-spacing and level-spacing-ratio distributions of real eigenvalues, each of which is unique to the symmetry class. Furthermore, we analyze spacings of real eigenvalues in physical models, such as bosonic many-body systems and free fermionic systems with disorder and dissipation. We clarify that the level spacings in ergodic (metallic) phases are described by the universal distributions of non-Hermitian random matrices in the same symmetry classes, while the level spacings in many-body localized and Anderson localized phases show the Poisson statistics. We also find that the number of real eigenvalues shows distinct scalings in the ergodic and localized phases in these symmetry classes. These results serve as effective tools for detecting quantum chaos, many-body localization, and real-complex transitions in non-Hermitian systems with symmetries. |
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N00.00211: Variable Memory: Beyond the Fixed Memory Assumption in Memory Modeling Arjun Karuvally, Hava T Siegelmann Memory models play a pivotal role in elucidating the mechanisms through which biological and artificial neural networks store and retrieve information. Traditionally, these models assume that memories are pre-determined, fixed before inference, and stored within synaptic interactions. Yet, neural networks can also dynamically store memories available only during inference within their activity. This capacity to bind and manipulate information as variables enhances the generalization capabilities of neural networks. Our research introduces and explores the concept of "variable memories." This approach extends the conventional sequence memory models, enabling information binding directly in network activity. By adopting this novel memory perspective, we unveil the underlying computational processes in the learned weights of recurrent neural networks on simple algorithmic tasks -- a fundamental question in the mechanistic understanding of neural networks. Our results underscore the imperative to evolve memory models beyond the fixed memory assumption towards more dynamic and flexible memory systems to further our understanding of neural information processing. |
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N00.00212: Comparison and interaction of micro and macro scale in living neural networks. Lochan Chaudhari
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N00.00213: Statistical mechanics and entropic repulsion of nanoscale origami Matthew J Grasinger Origami is a kind of scale invariant paradigm for morphing robotics, deployable structures, and metamaterials with tunable thermal, mechanical, or electromagnetic properties. There has been recent interest in using origami principles, along with DNA or graphene (among other materials), to design a wide array of nanoscale devices. However, to properly understand the behavior of these origami-based nanodevices, one must consider the interplay of the geometric mechanics of origami with thermal fluctuations, steric repulsion, van der Waals attraction, and other molecular-scale phenomena. Here we develop a model for the statistical mechanics of folded molecular sheets by drawing inspiration from past work on entropic pressure between biological membranes. We use the model to investigate 1) the thermodynamic multistability of molecular origami structures (i.e. multiple local minima of free energy) and 2) the rate at which thermal fluctuations drive its unfolding–that is, its temporal stability. We find that both the thermodynamic multistability and temporal stability have a nontrivial dependence on the origami's bending stiffness, the radii of curvature of its creases, the temperature, and its interfacial energy (between folded layers). We conclude with a brief discussion of how, given a material of interest, the fold pattern may be designed towards transforming nanostructures or molecular origami nanocomposites. |
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N00.00214: The XY-model as a Neuromorphic System, trained via Equilibrium Propagation Qingshan Wang, Clara Wanjura, Florian Marquardt The recent explosion of resources needed to train and run deep neural networks provides an urgent motivation for novel hardware designs which allow us to efficiently implement the functionality of neural networks in physical systems. One of the greatest challenges for such neuromorphic systems is efficient training, preferably based on physical interactions. |
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N00.00215: Interevent Time Correlations for Avalanches on a Conical Bead Pile. Kelly Kim, Susan Y Lehman
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N00.00216: Title:Poster: Persistence in Active Turbulence Amal Manoharan Active fluids such as bacterial swarms, self-propelled colloids, and cell tissues can all display complex spatio-temporal vortices that are reminiscent of inertial turbulence. This emergent behavior despite the overdamped nature of these systems is the hallmark of active turbulence. Using a generalized hydrodynamic model, we present a study of the persistence problem in active turbulence. We report that the persistence time of passive tracers inside the coherent vortices follows a Weibull probability density whose shape and scale are decided by the strength of activity —contrary to inertial turbulence that displays power-law statistics in this region. In the turbulent background, the persistence time is exponentially distributed that is remindful of inertial turbulence. Finally we show that the driver of persistence inside the coherent vortices is the temporal decorrelation of the topological field, whereas it is the vortex turnover time in the turbulent background. |
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N00.00217: Poster: Mapping parameter dependence for tunneling and entanglement dynamics in the kicked top Alex Gran, Arjendu K Pattanayak, Alexander Kiral, Noah J Pinkney, Sudheesh Srivastava We study the Quantum Kicked Top (QKT) as a function of nonlinearity K. Using adiabatic evolution of the parameter, we uncover the phenomenon even when the original spectrum is recovered the states have been shuffled(also termed exotic quantum holonomy). Further, we use measures of spectral bunching and averaged inverse participation ratios across phase-space to identify K values that yield unusual many-body quantum dynamics. In particular, for the 4 qubit QKT we find unusual dynamics for both linear entropy and tunneling at non-obvious K values 4π/3, 2π, ~2.76π, 4π corresponding to sharply-defined local minima in K for spectral bunching. We also see differing K-periodicities for the 4 qubit QKT with the period of 4π for the linear entropy, 8π for measures of tunneling and spectral bunching, and 16π for the adiabatically unrave led spectrum itself. Finally, we show that with increasing number of qubits n, the density of these local minima increases along with the K period, nonlinearly accelerating the number of K values with these degeneracies. We discuss the N → infinity limit. |
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N00.00218: Complete global synchronization of van der Pol oscillators Seido Nagano Complete global synchronization of van der Pol oscillators |
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N00.00219: Title: Graph Theoretic Approach to Investigationg the Critical Thresholds at which Galaxy Filamentary Structures Form Sophia-Gisela Strey, Alexander Castronovo, Kailash Elumalai Numerical simulations and observations show that galaxies are not uniformly distributed. In cosmology, the largest known structures in the universe are galaxy filaments formed from the hierarchical clustering of galaxies due to gravitational forces. These consist of "walls" and "bridges" that connect clusters. Using the Julia programming language, this study takes a graph theoretic approach to model these structures as euclidean networks in three dimensional space. Continuing with a method borrowed from statistical physics and percolation theory, cosmological graphs are reduced based on the valency of nodes to reveal the inner, most robust structural formation. By constraining the network, we are able to identify a threshold for physical features such as length-scale and density, at which galaxy filaments in clusters can be identified. |
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N00.00220: Interactions between crumples in elastic sheets Damian Gimeno, Robert S Hutton, Josh Rudfelt, Gavin Fisher, Eugenio Hamm, James Hanna Crumples are localized regions of elastic deformation in thin sheets. Experiments on bent and sheared sheets reveal two primary types of interaction between crumples, along ridges or valleys, leading to two types of crumple pairs. These pairs can further arrange themselves into one-dimensional patterns. We experimentally measure the force associated with creating and breaking these "bonds" between individual crumples, and between pairs. |
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N00.00221: Phase transitions beyond criticality: using analytic corrections to extend the validity of renormalization group scaling David Hathcock, James P Sethna The renormalization group predicts universal scaling laws near critical phase transitions. But can we extend this understanding of the critical point to accurately capture the behavior throughout the surrounding phases? To this end, normal form theory provides a useful framework: analytic variable changes (in temperature or field, for example) extend the universal scaling function to the entire phase. We apply this idea to the 2D Ising model, where Onsager's exact solution allows for quantitative tests of the accuracy of analytic corrections. By working in a special coordinate frame, in which the Fisher zeros lie on a straight line, we produce expansions of the free energy that converge for all temperatures. Even with minimal knowledge of the critical point, fitting the expansion to data (low- and high-temperature cluster expansions) deep within the phases also produces an exponentially convergent approximation, accurately capturing both the phases and phase transition. Finally, we discuss preliminary work and challenges on extending our approach to the 3D Ising model and systems in an external field. |
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N00.00222: Water-like thermodynamic anomalies in an analytically solvable 1D model Bruno Mota, Mariana Mallard For something so ubiquitous and essential to human life, the water molecule is surprisingly unusual. Water molecules are highly polar, and can interact through either short-range Van de Waals interactions or by forming slightly longer-range hydrogen bonds. Collectively, they can be found in a number of phases. Uniquely among small molecules, it has a solid phase that is less dense than a liquid phase, a result that is counter-intuitive on entropic grounds alone. |
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N00.00223: Lee-Yang theory, complex phase diagram, and supercritical matter Xiaoyu Ouyang, Xinzheng Li, Qijun Ye The supercritical region is often described as uniform with no definite transitions.The distinct behaviors of the matter therein, e.g., as liquid-like and gas-like, however, indicate their should-be different belongings. Here, we provide a mathematical description of these phenomena by revisiting the Lee-Yang (LY) theory and using a complex phase diagram, e.g. a 4-D one with complex T and p. Beyond the critical point, the 2-D phase diagram with real T and p, i.e. the physical plane, is free of LY zeros and hence no criticality emerges. But off-plane zeros in this 4-D scenario still come into play by inducing critical anomalies for different physical properties. This is evidenced by the correlation between the Widom line and LY edges in van der Waals model and water. The present distinct criteria to distinguish the supercritical matter manifest the high-dimensional feature of the phase diagram: e.g. when the LY zeros of complex T or p are projected onto the physical plane, a boundary defined by isobaric heat capacity Cp or adiabatic compression coefficient KT emanates. These results demonstrate the incipient phase transition nature of the supercritical matter. |
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N00.00224: FLUID DYNAMICS
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N00.00225: Thermal diffusivity measurements in sheared neutrally buoyant granular suspension Merin A.P. Heat transport in granular suspensions is an important yet underexplored area with applications in inkjet printing, geological flows, and fluidized bed reactors. However, current understanding of their heat transfer properties is limited, with most research focusing on flow anomalies. This study examines the effective thermal diffusivity of sheared granular suspensions with neutrally buoyant particles in a thin gap Taylor-Couette cell. A steady canonical shear flow is generated with Taylor instabilities suppressed by outer cylinder rotation. Thermal diffusivity of the medium is deduced by temporal temperature decay on the inner cylinder surface. Spherical 1 mm polystyrene and 2 mm PMMA particles were used with density-matched propylene glycol-glycerol solution. The study documents the effects of Peclet(<100) and particle Reynolds numbers(<30) on a suspension with four different volume fractions from 10-40%. |
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N00.00226: Diffusion-mediated Spinodal Decomposition in Ternary Mixtures Tejas Dethe, Niki Abbasi, Howard A Stone, Andrej Kosmrlj Ternary mixtures can undergo phase separation in response to concentration changes. It has been observed that a ternary mixture of oil-water-ethanol in a microchannel with water leads to the formation of a phase separating front, leaving oil- and water-rich stripes in its wake due to ethanol diffusion out of the mixture. We explore these dynamics via a system that is comprised of a stable ternary mixture and a stable single component phase in contact. This interface allows for the preferential diffusion of component 3 out of the mixture (mimicking ethanol), causing the mixture to become unstable and undergo spinodal decomposition from the interface. By rewriting a Flory-Huggins free energy, assuming for simplicity that the interaction parameters involving component 3 are zero, we get an effective binary mixture description, parameterized by component 3. This allows the ternary mixture to potentially become unstable once component 3 concentration goes below a cut-off value. Using Cahn-Hilliard dynamics, we explore features of diffusion-mediated patterns such as length scale, phase composition, and front velocity. We can then extend this model to microfluidic systems for industrial use such as aqueous two-phase co-flows, where advection can affect the phase separated patterns. |
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N00.00227: How to (numerically) calculate tortuosity in porous media? Maciej Matyka, Damian Śnieżek, Sahrish Naqvi, Dawid Strzelczyk, Krzysztof Graczyk Tortuosity is the third parameter (after porosity and permeability) that is most often computed in investigation of transport through porous media. It characterizes the elongation of emergent paths of diffusive, hydrodynamic or electric transport.
In this poster we will present several ways of tortuosity computation. Initially, we spotlight the streamline-based approach. To facilitate this, our docker-integrated OpenFOAM (FVM) framework —engineered to efficiently construct porous media and execute pore-scale fluid flow simulations — will be supplemented with Python script to compute multiple streamlines. We will then compare results derived from this method with those from the velocity-based procedure. The poster will shed light on the challenges posed by these methodologies, especially in conditions like the inertial regime where non-linear dynamics become prominent. Additionally, the discourse will touch upon meshless interpolation techniques suitable to both for streamlines as well as for the Lattice Boltzmann solver in the context of tortuosity. Concluding, we will explore a novel procedure utilizing a deep learning Convolutional Neural Network (CNN) approach, designed to determine tortuosity in randomized porous media. This approach proficiently calculates hydrodynamic and diffusive tortuosity. |
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N00.00228: Why is compressed wood weaker than natural wood in presence of moisture? Debapriya Pinaki Mohanty, Srinivasan Chandrasekar, Mysore Dayananda Recently, compression of wood has emerged as an attractive processing route to transform natural wood into high performance structural materials. While the wood strength is increased substantially by the compression, we show for the first time here, that, concomitantly, diffusion of water is enhanced by the compression. This discovery has come from studies with Balsa and Japanese Hinoki wood which contain controlled porosity. Because of the enhanced diffusion, densified compressed wood is weaker than natural wood in presence of moisture. The diffusion characteristics are related to the wood microstructure. In particular, we find that water diffuses mostly through the solid cell wall and very little via the pores. We obtain the diffusion coefficient of the cell wall material and find it to be an intrinsic property of the wood. The increased effective surface area for diffusion (cell wall) due to eliminating pores in compressed wood is what results in the higher diffusion, with adverse consequences for structural integrity. The directional effect of diffusion in wood is also controlled by the effective surface area distribution. Incidentally, the diffusion study has also provided insights into why nature has engineered specific porous structures in wood. |
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N00.00229: Fluids confined in quenched disordered porous media: Thermodynamics and dynamics Ankit Singh, Yashwant Singh We have developed a theory to calculate structural correlations, thermodynamic properties, and dynamics of a fluid confined within a random porous medium (matrix). Our study demonstrates that the quenched-disorder averaged excess free energy, arising due to the random potential fields of the matrix, can be organized to yield one- and two-body potentials for fluid particles. Averaging over disorder reduces the system to an effective one-component fluid system in which particles experience a one-body (external) potential and interact via an effective pair potential. The effective pair potential is a sum of the bare potential (the one present in the pure fluid) and the matrix-induced potential. The resulting partition function exclusively involves fluid variables. We derive equations for fluid-fluid and fluid-matrix correlation functions, as well as for the free energy, pressure, and chemical potential of the fluid. We utilize the results of pair correlation functions to determine the number of particles in a cooperatively reorganizing cluster (CRC) in which localized particles form "long-lived" nonchemical bonds with the central particle. For a relaxation event to occur, these bonds must reorganize irreversibly, and the energy involved in these processes represents the effective activation energy of relaxation. Our theory is applied to a model system of hard spheres, and we report results for the effective pair potential, correlation functions, thermodynamic properties, and dynamics. The effective pair potential is found to be attractive at the contact point and develops a repulsive peak before decaying to zero. Results for pair correlation functions, structure factor, and relaxation time are compared with simulation results for several fluid densities at two matrix densities. In all cases, a very good agreement has been found. |
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N00.00230: Microswimmers Unveil Novel Dynamical Phase in Active Nematics Partha Sarathi Mondal, Pawan Kumar Mishra, Shradha Mishra Active nematics has shown interesting dynamical and steady state properties: large-scale dynamic structures and collective flows, multi-spatial temporal dynamics etc. for pure active nematics. Whereas it also exhibits interesting dynamical and steady state features in the presence of external agents. Here, we focus on the properties of active nematics when the foreign agents are polar in nature. The example of such systems can be visualised as a collection of active apolar cells, where microswimmers are present as impurities. In this work we performed an extensive numerical study and showed that by varying the motility of microswimmers the background active nematics show an attractive dynamical state. Where the system evolves to a new dynamical rotating phase with the presence of vortices on the macroscopic scales, this phase appears at the cost of globally ordered active nematics. The motility of the microswmmers is responsible for such phase and this phase appears for intermediate range of motility, where microswimmers start to develop local clusters and coherent motion. Whereas the vortex state weakens when clustering of microswimmer increases for large motility. Hence our study provides a new interesting dynamical phase in active nematics, which can be completely tuned by controlling the motility of microswimmers and can be used for differentiating a variety of pathogens in apolar cells. |
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N00.00231: Poster: Visualizing Hydrodynamic Interaction of Scaled-up Flagella Model Daniel A Retic The physical swimming mechanisms used by microorganisms like bacteria are different compared to larger animals like humans. Escherichia Coli (E. Coli) bacteria use hair-like structures called flagella for locomotion. During translational movement, the flagella intertwine to create a bundle, the physical basis of which is not fully understood. To understand flagellar bundling, we created a macro model of four active flagella and one passive flagellum in silicon oil. We are testing if the four active flagella rotating together can give rise to sufficient drag in the surrounding fluid which is capable of propelling the passive one. The Reynolds number is kept constant with actual bacteria (~10^-2). We use Particle image velocimetry (PIV), using tracer particles and laser sheet. I will discuss the experimental design and computational implementation of PIV and then show results obtained in terms of the mean flow field and vorticity for a single model flagellum and how we can extrapolate that learning to our actual five flagella setup. |
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N00.00232: Gecko-inspired adhesive structures for amphibious soft robot locomotion. Sampada Acharya, Peter Roberts, Carmel Majidi, B Reeja-Jayan Over the years, efforts in bioinspired soft robotics have led to mobile systems that emulate features of natural animal locomotion. This includes combining mechanisms from multiple organisms to further improve movement. In this work, we seek to improve locomotion in soft, amphibious robots by combining two independent mechanisms: sea star locomotion gait and gecko adhesion. Specifically, we aim to test and compare various microstructures using different soft polymers to determine the optimal material with the corresponding microstructure configuration. We tested hemispherical, cylindrical and wedge-shaped microstructures made of PDMS and polyurethane to determine the adhesion on glass, acrylic, wood and metal surfaces. We determined the optimal geometric configuration for each type of microstructure by mathematically modeling the adhesion response of various geometric configurations. The gecko-inspired adhesives were subsequently subjected to experimentation on a compliant, pneumatically actuated limb, intended for integration into a soft robot inspired by sea stars. These adhesives, drawing inspiration from gecko adhesive structures, demonstrated a significant augmentation in adhesion properties across different substrates and enabled the robot to ascend inclines with a steepness of up to 25° and to maintain a stable grip on slopes inclined at 51° ± 6° under static conditions. |
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N00.00233: Understanding fundamental challenges to broadly-applicable nanofiber formation from thermoplastics via melt electrospinning Laura Clarke, Brenton D Boland, Neelam Sheoran, Jason Bochinski Although electrospinning (a technique where the presence of a strong electric field results in formation of a fluid cone-jet which transitions into a fiber) is a reliable approach to form polymer nanofibers from a wide range of soluble polymers, its use with melts is more problematic. The high viscosity of thermoplastic melts is incompatible with the most common electrospinning configuration (a long thin needle placed at high voltage through which the fluid must be pumped), intrinsically low ionic conductivity in melts results in relatively large jet diameters [1,2], and additional thinning from jet to fiber due to solvent loss is absent. Resolving these experimental challenges (i.e., utilizing an open flat-plate configuration where pumping is unnecessary and enhancing conductivity with commercial additives) results in a simple system where interactions between the melt and electric field can be visualized and understood to push towards nanofiber formation. In this poster, we discuss controlling flow rate via melt film thickness, manipulating the number of jets to further choke flow, and tracking the transition from jet to fiber: strategies which enable ultimate formation of linear low density polyethylene nanofibers. |
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N00.00234: Eggless Vegan Food Emulsions Nadia Nikolova, Lena Hassan, Angelica Ramirez, Stefan Baier, Vivek Sharma Food emulsions like mayonnaise, remoudale, French aioli, rouille, etc that are used as dressing, dips, or sauce bases are often egg-based. In this poster, we present the challenges and opportunities in emulating such emulsion recipes using plant-based proteins. We focus primarily on emulsification, shelf-life, dispensing, processability and consumer experience or preferences set by the flow behavior. We characterize the shear and extensional rheology response of animal and plant-based emulsions and study the interfacial and bulk rheology of protein-polysaccharide mixtures utilized in making such emulsions. |
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N00.00235: Strategies for designing sustainable biomass microbeads for consumer application Benjamin Robertson, Michelle A Calabrese, Lena M Hoover, Jerry E Rott, Abbie F Nistler, Siena M Quinn, Audrey J Miller While plastic microbeads are useful as exfoliants and rheological modifiers in a wide range of personal care consumer products, billions of these primary microplastics enter the environment daily in the US alone, causing extensive environmental harm. Non-derivatized biomass, in the form of microcrystalline cellulose and Kraft lignin, presents an abundant sustainable alternative to plastic microbeads, but there are a number of processing challenges associated with shaping these forms of biomass into microbeads with the appropriate size, shape, and stiffness to compete with commercial plastics. The poor solubility of cellulose in most conventional solvents, combined with the high viscosities of cellulose solutions create difficulties in dispersing these solutions either through extrusion or emulsion techniques to attain microbeads of the appropriate size – hundreds of microns in diameter. To overcome these challenges, we tuned the extensional viscosity of biomass solutions to enable smaller beads from an extrusion method. Using lessons learned from this extrusion method, we developed our high-yield emulsion method to scalably produce biomass microbeads. Using this method, we tuned interfacial tension to create beads of the appropriate size with a wide range of morphologies, resulting in a viable platform to eliminate a major source of primary microplastics from widely available material. |
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N00.00236: Flow of a Non-Newtonian Liquid Around a Sphere Shayna Sit, Piotr Habdas When a sphere is pulled through a liquid with a yield stress, a fluidized region near the sphere is formed. Based on computer simulations, this region can be described as spindle torus shape. To determine the size of the fluidized region, we pulled steel spheres through tubes of different diameters filled with a non-Newtonian fluid. By measuring the drag force on the sphere as a function of container size we determined the extent of the fluidized region surrounding the sphere. Also, we found that the drag force is not proportional to the velocity, as it is for Newtonian fluids. To study the shape of the fluidized region around the sphere, poppy seeds were scattered throughout the non-Newtonian liquid. Using particle tracking techniques we tracked the position of the poppy seeds and visualized the fluidized region as a steel sphere moved through the liquid. |
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N00.00237: Flat disc suspensions are indistinguishable from macromolecular solutions within planar incompressible flows Stylianos Varchanis, Fabian Hillebrand, Rebecca Hill, Mahdi Davoodi, Amy Q Shen, Robert J Poole We prove analytically that the two fundamental rheological equations for flat disc suspensions and macromolecular solutions, the so-called Oldroyd-A and -B models, respectively, produce identical velocity fields in any planar incompressible flow. We demonstrate that this has significant implications for understanding and controlling nonlinear flow phenomena, such as elastic instabilities and elastoinertial turbulence. We use numerical simulations of Oldroyd-A/-B fluids to illustrate this equivalency in two benchmark flows: the creeping flow in a cross-slot channel and the onset of elastoinertial turbulence in a planar channel. |
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N00.00238: Effects of cosolvent addition on the extensional rheology of PNIPAM solutions Diana Y Zhang, Alec J Schwendinger, Michelle A Calabrese Poly(N-isopropylacrylamide) (PNIPAM), a thermoresponsive polymer known for its lower critical solution temperature (LCST) of ~32 °C in aqueous media, has been studied for a wide range of applications including drug delivery, sensing, and smart coatings. PNIPAM chains undergo a conformational change from hydrated coils in solution below the LCST to collapsed globules that often aggregate above the LCST. Polymer chain conformation significantly affects the amenability of solutions to extensional flow-dominated processes such as spraying and printing, which are of interest for manufacturing coatings and devices at-scale. Adding a cosolvent can change the PNIPAM solution phase windows and thus be leveraged to tune processing windows. Herein, we use dripping-onto-substrate extensional rheometry (DoS) to measure the extensional flow behavior of PNIPAM in dimethylformamide (DMF)/water mixtures. We demonstrate the effects of DMF fraction on two PNIPAM polymers of different molecular weight and dispersity. Most notably, while the LCST exhibits a maximum with increasing DMF content as determined by turbidimetry measurements, the extensional relaxation time (λE) increases monotonically within the same range. At a given xc, λE exhibits an anomalous trend with polymer concentration regardless of polymer molecular weight and dispersity. These results suggest that preferential PNIPAM-DMF interactions evolve with solvent composition in line with prior studies. |
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N00.00239: Spreading, pinching, and coalescence: the Ohnesorge units Vivek Sharma, Marc-Antoine Fardin, Mathieu Hautefeuille Understanding the kinematics and dynamics of spreading, pinching, and coalescence of drops is critically important for a diverse range of applications involving spraying, printing, coating, dispensing, emulsification, and atomization. Hence experimental studies visualize and characterize the increase in size over time for drops spreading over substrates, or liquid bridges between coalescing drops, or the decrease in the radius of pinching necks during drop formation. Even for Newtonian fluids, the interplay of inertial, viscous, and capillary stresses can lead to a number of scaling laws, with three limiting selfsimilar cases: visco-inertial (VI), visco-capillary (VC) and inertio-capillary (IC). Though experiments are |
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N00.00240: Thickness of nano-scale poly(dimethylsiloxane) layers determines the motion of sliding water drops Xiaoteng Zhou, Hans-Juergen Butt, Xiaomei Li, Yuki Nagata, Rüdiger Berger, Kaloian Koynov, Katrin Amann-Winkel, Pranav Sudersan, Yongkang Wang Nanometer thick layers of polydimethylsiloxane (PDMS) are widely applied as hydrophobic coatings because they are environmentally friendly and chemically inert. In many applications, low friction of water drops is required. While the onset of motion (static friction) has already been studied, dynamic friction is less explored. It is not understood which processes lead to energy dissipation and cause friction. Such knowledge is important to minimize drop friction for applications such as heat exchangers or fog harvesting. Here, we measure dynamic friction of water drops on PDMS layers with different thickness and architecture over the whole available velocity regime. The layer thickness L turned out to be a good predictor for drop friction. 4-5 nm thick PDMS layers showed the lowest dynamic friction. A certain minimal layer thickness seems to be necessary to form homogeneous surfaces and reduce the attractive interaction between water and the underlying substrate. The increase of friction above L = 4-5 nm is attributed to PDMS meniscus formation at the contact line due to the surface tension of water. When the contact line moves, the meniscus is dragged across the surface. Energy is dissipated due to stretching of chains and viscous dissipation. AFM force and friction measurements support this interpretation. The effect may be enhanced due to an increasing viscosity of the PDMS layer caused by entanglement of the polymer chains. |
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N00.00241: Rolling in circles: the mysterious dynamics of superparamagnetic Quincke rollers Eavan Fitzgerald Quincke rotation occurs when a dielectric particle in a conducting fluid rotates spontaneously in response to an externally applied DC electric field E. Above a threshold value Ec, for particles near a surface, friction converts rotation into rolling in the plane orthogonal to E at a constant speed set by the field. Typical Quincke systems showcase individual random walks, with collective motion emerging at sufficient densities. We introduce an additional degree of freedom using superparamagnetic (SPM) particles, and observe markedly different dynamics. With no magnetic field B, particles execute tight circular trajectories or even orbits. These are more unstable at higher E fields, as periods of circular motion may be interspersed with short “walks”. We also find that the rolling speed now scales with |E|α, α ≥ 2. Introducing a homogeneous in-plane B in addition to E, linearises the circular motion, causing flows perpendicular to the magnetic field lines. For a fixed E ≥ Ec, rolling speed remains independent of the applied B field. Unlike other recent work on SPM rollers, we observe no enhanced particle interactions, e.g. chaining. While the origin of the circular motion remains elusive, the switch to linear motion in a non-zero B field suggests the particles’ intrinsic magnetic properties are critical in determining their dynamics. |
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N00.00242: Determining Heterogeneous Nucleation Rates of Mg(OH)2 on MgO Using Multiharmonic QCM-D and X-ray Scattering methods Pedro Josue Hernandez Penagos, Masiel Velarde, Christopher M Rouleau, Ke Yuan, Ilia Ivanov, Jose L Banuelos, Juliane Weber Mineral looping using MgO is a promising approach for direct air capture (DAC) of CO2 from the atmosphere at the gigaton/yr scale. One initial step during the MgO carbonation process in the presence of humidity is brucite formation, Mg(OH)2, as a possible passivating phase on MgO surfaces. The influence of temperature and relative humidity variation on heterogeneous nucleation and crystal growth kinetics of Mg(OH)2 on MgO are not well understood under environmentally/DAC-relevant conditions. In this project, quartz crystal microbalance (QCM) commercial crystals were coated with a ~90nm-thick MgO film using pulsed laser deposition (PLD). Similar films were also deposited using RF magnetron sputtering. Atomic force microscopy characterization of PLD-deposited films showed a roughness of 0.21 nm and domain size of ~40-60 nm. Experiments to investigate brucite formation using multiharmonic QCM with Dissipation analysis (QCM-D) were conducted by flowing deionized water at 20 µl/min over the MgO film, as well as under water vapor exposure. This work allowed estimates of dissolution and growth rates by analyzing the time-dependence of mass loss under each experimental condition. Results of QCM analysis using first and second order kinetic models will be presented along with x-ray grazing incidence scattering and reflectivity results to relate molecular and nanoscale structural changes to the QCM studies. |
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N00.00243: Phase Separation of Homopolymer Blended Liquid Crystal Elastomers(LCE) for Creation of Porous Structures Akhila Joy Liquid Crystal elastomers (LCE), with their combination of ordered Liquid Crystal structure and rubber-like elasticity, enable anisotropic responses to external stimuli and efficient transduction of thermal and light energy into reversible mechanical deformation. LCEs are ideal for manufacturing self-driven actuators with complex deformations, and porous LCEs are particularly sought after for their exceptional deformation capabilities. The introduction of porosity reduces density, enhances processability, and increases the surface area available for interaction with external stimuli, all of which offer distinct advantages over solid LCEs. This versatility has led to a wide range of potential applications, including soft robotics, drug delivery, 3D cell scaffold, and sensor technology. In this work, homopolymers are incorporated into the LCEs as a sacrificial domain through blending. Our focus is to fundamentally understand the phase separation behavior of homopolymer in LCE and the relationship between parameters and structure changes, thereby evaluating the actuation performance of the resulting LCEs with controllable porous structures. |
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N00.00244: Interface-Mediated Electrospray Deposition: Understanding the Efficacy of Material Delivery using Substrate Focusing Methods Joseph M Prisaznuk, Xin Yong, Peter Huang, Paul R Chiarot The field-driven nature of electrospray gives it the unique ability to deposit conformal coatings onto a wide range of substrates. The microstructure of these thin films tend to be limited by the spray parameters, such as voltage, suspension volatility, and particle size. Instead of depositing particles to a dry substrate directly, we introduce a water-air interface as the target in order to "reconfigure" the microstructure before the liquid completely evaporates. In this work, we employ a range of thin (0.2 - 1.0 mm) dielectric masks attached to a conductive substrate serving two functions: 1. to define the position of the target droplet contact line and 2. to focus the electrosprayed material towards the waiter-air interface. We primarily consider the case of spherical cap droplets with r = 0.5 or 1 mm, as these are close to the resolution limit of our additively manufactured masks. In addition to the 3D printed ABS/PLA masks we tested FR4 as a focusing material, and observed a reduction in material delivery efficiency. We believe this may be caused by increased charge mobility on the surface of the mask, which would allow the positive electrostatic charge deposited by electrospray to dissipate or redistribute faster than expected. Finally, we can also evaluate the effect of focusing material thickness. By understanding the relationship between mask geometry, material properties, and deposition efficacy, we can find the optimal substrate modifications for our system. |
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N00.00245: Modeling Incipient Erosion and Quantifying Erosion Rates with A Computational Fluid Dynamics Framework Mitchell D Jans, Ian C Bourg Predicting fine-grained sediment erosion is important for evaluating geochemical cycling, contaminant transport, and is foundational to fluvial geomorphic processes. Previous attempts to create predictive models have been insufficient due to the complex hydro-mechanical-chemical couplings that exist between fine-grained particles resulting in mechanically notable particle-particle interactions. In this work, we base our study on our previously developed Darcy-Brinkman-Biot framework. This framework represents clay erosion by incorporating sub-REV (Representative Elementary Volume) properties of bentonite, calculating clay-water momentum transfer quantities, and allowing for phase flow through and around deformable porous media. |
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N00.00246: Inverse design and optimization of stochastic particle dynamics in complex flows Alp M Sunol, Kaylie Hausknecht, mohammed alhashim, Michael P Brenner Understanding and controlling stochastic particle dynamics carries great significance for a wide array of industrial and biophysical processes. Despite their significance, the precise control of such dynamics has remained elusive. The recent emergence of efficient automatically differentiable simulation techniques suggests gradient-based optimization methods as promising approaches to inverse problems in complex physical systems. In this work, we expand upon a previously developed fully-differentiable numerical framework that combines a computational fluid dynamics solver (JAX-CFD) with molecular/Brownian Dynamics (JAX-MD). We account for fluid flow in complex geometries using immersed boundary methods, while explicitly representing the stochastic equations of motion governing suspended particles, which can range from the Brownian motion of colloids to the run-and-tumble motion of bacteria. Our implementation can be used for both optimization problems and data-driven model parametrization. We demonstrate the effectiveness of our approach on a diverse range of novel problems, including optimizing geometry to mitigate upstream migration of bacteria in biomedical devices and fine-tuning fluid properties to obtain desired flow characteristics through heterogeneous porous media. |
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N00.00247: Traveling wave solution of a thermoviscous liquid film on a vertical cylinder Garima Singh, Naveen professor A liquid film coating a cylindrical substrate is unstable to interfacial disturbances governed by Rayleigh-Plateau instability. These initial disturbances grow in time and beyond saturation, develop into a train of traveling waves, wherein the droplets of equal amplitude form at periodic intervals moving downstream at the same speed. Our study focuses on these traveling waves formed by a thermoviscous fluid falling on the outside surface of a vertical cylinder. We treat these traveling waves as a steady state film profile in a moving reference frame. The effects of Bond number, Marangoni number, thermoviscosity number and Biot number have been studied on the film profile and traveling wave speed. Smaller values of Bond number result in larger amplitudes and wave speeds. For a finite value of Biot number, an increase in thermoviscosity number is found to decrease the wave speed and increase the wave amplitude. Furthermore, the effect of Biot number is found to be dependent on the thermoviscosity number and can also result in non-monotonic variation in the wave amplitude. |
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N00.00248: Visualizing a Black Hole Event Horizon using a Light-Sensitive Reaction-Diffusion System Veran Stanek, Taliah G Lansing, Augustus Thomas, Daniel Cohen-Cobos, Niklas Manz We are using chemical reaction-diffusion waves to visualize a black hole event horizon. The event horizon of a black hole is the radius from its center of gravity at which not even light can escape its gravitational pull, but light is able to enter this region. In our table-top analog, we employ the chemical Belousov-Zhabotinsky (BZ) reaction to create easily visible fronts moving in a quasi-two-dimensional system. The black hole is created through a radially symmetrical light gradient with increasing intensity going outward until it reaches a maximal radius, at which the light intensity become zero again – as in the central region. BZ waves created outside our circular light gradient can pass the sharp intensity jump and enter the center regions. BZ waves created at, for example, the center, propagate outward – up the light intensity gradient – but die before reaching the maximal radius. Our experiments are supported by Python simulations using light-sensitive reaction-diffusion waves, replicating our experimental observations. |
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N00.00249: Using Reaction-Diffusion Waves to Visualize Electron Drift Velocity Augustus Thomas, Mahala Wanner, Daniel Cohen-Cobos, Niklas Manz We are using chemical reaction-diffusion waves to visualize the drift velocities of electrons in conductors. Though electrons move very fast, the actual drift velocity along the wire is surprisingly small. In our table-top analog, we employ the chemical Belousov-Zhabotinsky reaction to create easily visible, colorful fronts moving in quasi-one-dimensional channels. The initial chemical composition of the solution defines the electron drift velocity. Using several parallel channels, each filled with a slightly different solution, we can create observable fronts propagating at different speeds. As a result one can compare different conductors (number of free electrons n), applied currents I, or wire radii r on the electron drift velocity in a real material. Our experiments are supported by Python simulations using reaction-diffusion waves, connecting the desired variables n, I, and r with necessary component concentrations. |
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N00.00250: Magnetic field effects on the surfactant concentration over ferrofluid droplet surfaces in shear flows Rodrigo B Reboucas, Paulo H Pimenta, Juan L Barbosa, Taygoara F Oliveira In this work we investigate the impact of a magnetic field on surfactant concentration and interfacial forces across droplet surfaces within shear flows. Our analysis centers on a single two-dimensional ferrofluid droplet covered with surfactants, suspended in an immiscible, non-magnetizable liquid. The model combines incompressible Navier–Stokes equations and Maxwell's equations in the superparamagnetic limit in the single-fluid formulation, augmented by terms accounting for Marangoni, capillary, and magnetic forces at the droplet interface. We solve the surfactant convection-diffusion equation at the surface, while a non-linear Langmuir equation of state relates surfactant concentration to surface tension. The model is numerically solved using finite differences, a level-set method for multiphase flow computation, and the closest-point method for concentration equation. Our findings reveal that even though the surfactant is magnetically neutral, the presence of a magnetic field significantly modifies its distribution at the interface. A magnetic field perpendicular to the primary flow direction shifts the maximum concentration zone from the droplet tips toward the flow vorticity direction, while a parallel field produces the opposite effect. Alterations in surfactant distribution directly impact the surface tension field, offering a potential wireless means of controlling droplet dynamics. |
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N00.00251: Analyzing energy flux in experiments to determine the reflection coefficient of internal waves beams that reflect from varied surfaces Bruce E Rodenborn, Olivia C Roach, Kaden Huiet, Michael Allshouse, Luke Payne Internal wave beams do not propagate long distances in the ocean, and we hypothesize that dissipation upon reflection contributes to scattering wave energy. We study how boundary roughness in our tank experiments affects the reflection coefficient: the ratio of the outgoing energy flux to the incoming energy flux through a surface near the reflection region. We measure the velocity field using particle image velocimetry and determine the energy flux using the work of Lee et al. (Phys. Fluids, 26, 2014). The wave beams are separated using the Hilbert transform method of Mercier et al. (Phys. Fluids, 20, 2008) to calculate the contributions from the incoming wave beam and any harmonic waves. We find high energy dissipation rates (small reflection coefficients) for steep boundary angles or when the boundary is roughened. We also find significant wave energy reflected back from the boundary towards the generation site under these same conditions. |
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N00.00252: Spontaneous Channelization in Draining Thin Film Suspensions Sage Eanet Spontaneous channelization is seen in many everyday draining thin film suspensions, such as yogurt draining down the side of a vertical glass. Furthermore, channelization is also observed as the result of large-scale erosional events including debris flows and mudslides, such as those seen in Montecito, CA in 2018. We hypothesize that there may be some link between these similar phenomena and use small scale thin film flow experiments to attempt to replicate the channelization behavior. Prior research on this topic consists only of one study attributing this behavior to colloidal gelation of particles (Buchanan et al.; 2007); however, channelization is observed in repulsive particles as well, leading us to suspect contribution from another mechanism. We produce channels in the lab using suspensions of quartz particles of varying sizes. Trials including the use of surfactants suggest the importance of the role of capillary action in the channelization process. We propose a phase space of channelization in draining thin film suspensions consisting of the interactions between capillarity and gravity driven flows. We explore the scalability of the capillary process by varying the experimental scale in the lab, with the aim of generalizing the channelization mechanism to explain mudslide behavior as well as commonplace phenomena. |
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N00.00253: Study of mixing enhancement in microfluidic channels through extensional flows Chandrasekhar Kothapalli, James S Taton A micromixer design is proposed that incorporates both shear and extensional flows to promote enhanced mixing in laminar flow systems. The shear flows result from the centripetal forces experienced by the fluid being forced to move along a serpentine channel. The elongational flows result from periodic hyperbolic constrictions placed in the path of the fluid, that subject the fluid to constant stress rates. The result of the overlapping two effects on the fluid dynamics is analyzed using computational fluid dynamics, for a broad range of constriction geometries in terms of width and length. The mixing performance of the designs is quantified both in terms of the absolute value of the mixing index, as well as in terms of the energetic cost of mixing associated with the needed pressure differential. This allows for optimal designs to be identified across Reynold numbers ranging from 10 to 100. |
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N00.00254: A 2D microfluidic model of cerebrospinal fluid motion in periarterial spaces Sasha Toole, Kerstin Nordstrom The glymphatic system is a pathway for metabolic waste clearance in the brain. In a crucial step of this pathway, cerebrospinal fluid (CSF) enters the brain via periarterial spaces. Previous studies in live mice have found that peristaltic waves in the arterial wall, driven by pulsatile blood flow, can induce the flow of CSF in the surrounding periarterial space. However, the exact mechanism driving CSF flow remains unclear among multiple possible contributing mechanisms. We developed a microfluidic device that serves as a two-dimensional model of the arterial wall interface between the periarterial space and inner artery to study the flow of peristaltically driven CSF. With this microfluidic model, we found that the induced flow oscillates with each pulsation of the peristaltic wave and travels in the same direction as the wave, with the bulk forward flow decreasing with higher frequency. We additionally found a promising power law relationship between the Root-Mean-Squared velocity of the induced flow and frequency. These observations contribute new insight to the understanding of CSF flow mechanisms. |
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N00.00255: BIOLOGICAL PHYSICS
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N00.00256: Investigating the Conformational Dynamics of the Enzyme Guanylate Kinase from Mutations at Two Locations Nathan Avey, Zahra Alavi In this study, we look at the conformational dynamics of the enzyme Guanylate Kinase (GK), as well as 3 mutants of the enzyme. Achieving mutations with significant functional change to the protein is generally the result of many changes to the sequence of amino acids, but in the case of GK, we see that with only two mutations have caused changes in the enzyme activity. This mutant is the result of Alanines in residue 175 and 176 being changed to Glycine. Taking use of molecular dynamics, docking, and free energy profiles we provide a full description of the conformational changes of the three mutants. |
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N00.00257: Ligand-dependent, single protein conformational transitions and manipulation Yongki Choi, Sung Oh Woo, Philip G Collins Using a high-resolution single-molecule nanocircuit approach, we observed that enzyme conformational states and transitions are influenced by the specific ligands. In the case of lysozyme interacting with peptidoglycan substrates, it exhibited dynamic transitions between open, intermediate, and fully closed, hydrolysis-ready conformational states with occasional interruptions. However, when interacting with substrate analogs, lysozyme underwent minimal conformational changes, transitioning from an open to a slightly closed, excited state with rapid transition rates. Furthermore, we investigated the potential impact of non-thermal noise on these conformational transitions and its role in enzyme specificity and catalytic activity. |
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N00.00258: Structural ensemble determination of intrinsically disordered protein, NUPR1, by replica-exchange molecular dynamics simulation Seonghun Jang, Sangwook Woo Nuclear Protein 1 (NUPR1) is a transcription regulator and is involved in various diseases, including cardiovascular disease, inflammatory response, and cancer. NUPR1, 82 amino acid residue, is an intrinsically disordered protein (IDP), which is known to have no stable secondary and tertiary structure. NMR or SAXS can characterize the solution structure and dynamics of IDPs, but the ensemble structures revealed by those experimental techniques are rare and are not high-resolution structures. |
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N00.00259: A coarse-grained modelling approach to protein liquid-liquid phase separation: effect of recombinant protein length on self-assembly structures. Alberto Scacchi, Adam Harmat, Laura Lemetti, Yin Yin, Mengjie Shen, Markus B Linder, Sesilja Aranko, Maria Sammalkorpi Phase transitions play an essential role in the assembly of nature's protein-based materials into hierarchically organized structures, yet the underlying mechanisms and interactions remain elusive. A central question for designing proteins for materials is how the protein architecture affects the nature of the phase transitions and the resulting assembly. We examine the assembly of silk-like modular block proteins by a computational bead-spring model. We show that our model can underpin the transition from homogeneous solution to phase separation corresponding to assembly formation for various protein architectures, particularly protein chain length variation [1]. We find that in the assembly phase, a protein length- and concentration-dependent transition between two distinct assembly morphologies, one forming aggregates, and another coacervates, exists, both in the simulations and in our experimental characterization of the equivalent proteins with varying lengths. We deduce that properties and internal structures of the assemblies depend on the protein size. Our experimental data of silk-mimicking proteins support the model predictions. This approach can be extended to investigate other protein design variables. |
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N00.00260: Protein-lipid interactions and anchoring modulate binding between Prion and Doppel protein globular domains and lipid membranes Patricia Soto, Davis Thalhuber, Frank Luceri, Jamie Janos, Mason Borgman, Noah Greenwood The Prion protein is the molecular hallmark of the incurable prion diseases affecting mammals, including humans. The protein-only hypothesis states that the Prion protein plays a critical role in prion diseases by misfolding and accumulating into toxic aggregates. The cellular Prion protein (PrPC) anchors to cholesterol- and sphingomyelin-rich plasma membrane domains. Prion protein conversion happens on the cell surface and is sensitive to membrane composition. A picture of the underlying driving forces that explain the effect of protein - lipid interactions in physiological conditions is needed to develop a structural model of Prion protein conformational conversion. To this end, we characterize the driving forces behind Prion protein-lipid interactions under physiological conditions. Molecular dynamics simulations mimic the dynamics of anchored PrPC on model lipid patches. We also simulate the related Doppel protein on the same patches. Our simulations show that specific protein-lipid interactions and anchoring constraints favor particular binding sites on PrPC and, to a lesser extent, Doppel. Intriguingly, the binding sites of PrPC correspond to loops critical for aggregation and prion transmission. The membrane locally remodels to accommodate inserted protein residues. This work elucidates how interactions modulate the association of Prion and Doppel proteins with membranes to set the stage for understanding Prion protein conformational conversion. |
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N00.00261: Modulation of Actin Polymerization using Curved Nanotopographic Surfaces Jerry Shen, Mona Abostate, Corey Herr, John T Fourkas, Wolfgang Losert Exploring the mechanisms by which actin polymerizes and contributes to cell motility can offer valuable insights into biological processes such as cancer metastasis and wound healing. Structural factors, such as the surface features of the extracellular matrix, can influence how cells migrate. Previous research has suggested that nanotextured surfaces composed of parallel ridges may bias actin-wave polymerization bidirectionally along the ridges. However, extracellular environments are rarely composed of such well aligned surfaces. For better modelling of the heterogeneity in the extracellular environment, we sought to understand the cell sensing of Dictyostelium discoideum cells on curved nanotextured ridges. Fluorescently tagged actin in D. discoideum was imaged on several textures of varying degrees of curvature, and actin polymerization was characterized using optical flow. We show that curved textures modulate the degree of directional bias in actin polymerization. Surfaces with low levels of curvature retain the ability to bias actin polymerization, whereas surfaces with high levels of curvature strongly reduce polymerization bias. This effect appears to be associated with local alignment between actin polymerization and the ridge orientation. |
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N00.00262: A minimal mathematical model of cytoplasmic mixing in large motile cells Sam Silliman, Ulises Diaz, Wallace F Marshall, Moumita Das The cytoplasm of cells is a dynamic fluid with continuous mixing of cellular components. This mixing is vital for cell functions but is complicated by the cell's motion, shape changes, and crowding due to organelles and other sub cellular structures. The giant amoeba chaos carolinensis is an excellent model experimental system for studying cytoplasmic mixing thanks to its large size. While diffusion is sufficient for cytoplasmic mixing in relatively small cells, large cells rely on active mechanisms to facilitate cytoplasmic mixing. Motivated by this, we carry out agent-based simulations of a minimal mathematical model of the dynamics of tracer particles in a large motile cell with low to moderate internal crowding and deformable boundaries. We investigate the emergent cytoplasmic flow and mixing in this model system by characterizing the motion of the tracer particles in terms of their trajectories, mean squared displacements, and velocity correlations. We compare our results with experimental data and estimates of mixing timescales in various fluid flows, and discuss potential mechanisms for mixing in large cells. |
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N00.00263: The role of biomembrane in amyloid toxicity and small molecules protecting the membrane from amyloid-induced damage Nanqin Mei, Carina T Filice, Yue Xu, Danielle McRae, Zoya Leonenko Alzheimer’s disease (AD) is a neurodegenerative disease characterized by dementia and memory loss for which no cure or prevention is currently available. Amyloid toxicity is a result of non-specific interaction of toxic amyloid oligomers with the neuronal cellular membrane. |
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N00.00264: MEASURING HYDRODYNAMIC FORCE AND FRICTION ON LIPID ANCHORED PROTEINS Sreeja Sasidharan, Aurelia R Honerkamp-Smith, Damien Thévenin, Leah E Knepper, Samuel Pash, Emily Ankorm, Gabriel R Cuce, Lingyang Kong, Sang-Jun Park, Larissa Socrier, Yiwei Cao, Linda Lowe-Krentz, Wonpil Im Lipid-anchored peripheral membrane proteins differ from transmembrane proteins in their freedom to explore the entire outer surface of a cell. Flows of surrounding fluid can rearrange these proteins by pushing them to the downstream cell edge, and this transport may be involved in flow mechanosensing. Previously, we developed an experimental method for measuring flow-induced lateral transport of neutravidin bound to biotinylated lipids in model membranes. Making general predictions about flow transport of proteins requires quantitative estimates of the hydrodynamic force and membrane drag. Here, we measure forces from shear flow directly by extending our method to compare flow mobility for lipid-anchored protein constructs with different sizes but identical lipid anchors and membrane compositions. To eliminate uncertainty in the number of biotinylated lipid anchors bound to each protein, we used monomeric streptavidin (mSA). We generated a series of protein constructs with increasing size: mSA, mSA-GFP, and mSA-MBP. We then compared the flow mobility of these constructs with that of commercially available streptavidin. The mobility of proteins measured by the experiment follows the expected order of mSA-MBP> mSA-GFP > mSA, correlated with their size. Our measurements of mobility and diffusion allow us to calculate the hydrodynamic force applied by flow, which is proportional to the hydrodynamic area of each protein. We compare our experimentally determined hydrodynamic areas with values obtained from molecular dynamics simulations. The hydrodynamic forces we apply to the protein constructs are on the order of piconewtons, similar to the forces applied by blood flow to membrane proteins on cells located at blood vessel walls. To demonstrate that flow-mediated protein transport can occur on living cells, we measure the flow-induced lateral transport of GFP-tagged plasma membrane proteins of different sizes on living COS-7 cells. |
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N00.00265: Poster: Two-dimensional Nanoassemblies of Spherocylindrical Nanoparticles inside Lipid Vesicles Abash Sharma, yu zhu, Eric J Spangler, Mohamed Laradji Using molecular dynamics of a coarse-grained implicit-solvent model, we demonstrate that liposomes can induce the self-assembly of uniform spherocylindrical nanoparticles (SCNPs) on the liposomes’ inner surface. The characteristics of these nanoassemblies are contingent upon the adhesion strength, leading to the formation of unique quasi-two-dimensional polygonal and star-like nanoclusters. Our simulations reveal that, under low adhesion strength, the adhering spherocylindrical nanoparticles remain diffusive inside the vesicle. As the adhesion strength increases, the SCNPs assemble to form a regular polygonal geometry. The SCNPs self-assemble into interesting star-like nanocluster geometry as <!--[if gte msEquation 12]> style='mso-bidi-font-style:normal'>ξ i is further increased. The vesicles transform from a three-dimensional structure into a flattened two-dimensional geometry over a wide range of intermediate values of the adhesion strength. At high adhesion strengths, the SCNPs are exocytosed. Interestingly, the evolution of nanocluster geometries from three to two dimensions generates various polygonal and star-like geometries contingent on the nanoparticle count. Free energy calculations based on the Helfrich Hamiltonian are used to assess the stability of the various observed nanoassemblies. |
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N00.00266: Probing and controlling single-molecule interactions with force spectroscopy sakurako tani, Lina A Alhalhooly, Yongki Choi Atomic force microscopy and dynamic force spectroscopy techniques provide the means to explore the spatial distribution of membrane surface receptors and their dynamic interactions with ligands. In this work, we investigated several ligands including integrins at different loading rates. We found a linear relationship between the binding strength of ligand-receptor and the logarithmic loading rate, suggesting that the unbinding process follows the Bell-Evans two-state transition model. Using the energy landscapes constructed from dynamic force measurements and the Kramers escape rate from bound to unbound state under an external force, we evaluated kinetic and thermodynamic parameters, including the potential energy barrier height, kinetic off rate, and the width of the potential well, governing the ligand-receptor transitions between the two states. We discuss the potential of adjusting these parameters to influence the specificity, affinity, and stability of the single-molecule interactions. |
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N00.00267: Abstract Withdrawn
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N00.00268: Equilibrium behavior in phospholipid monolayers: morphology, branching curvature, and stripe width. Benjamin L Stottrup, Zachary McAllister, Bjorn H Solberg, Abram Cressman, Anjiya Panjwani, Cain Valtierrez, Joseph A Zasadzinski Phospholipid monolayers are a valuable model system to investigate the two-dimensional physics of soft thin film systems. The availability of enantiomers of Dipalmitoylphosphatidylcholine (DPPC) in purified form allows us to investigate the chiral nature of model lipid monolayers through fluorescence microscopy and traditional Langmuir thermodynamic techniques. These phospholipid monolayers are the primary lipid component of lung surfactant -necessary for proper respiration. We focus on mixtures of DPPC with cholesterol, hexadecanol (HD), and palmitic acid (PA), which have been previously studied and shown to form equilibrium morphologies over experimental time scales REF: Valtierrez et al., Sci. Adv. v:8:14, 2022. In this poster, we will assess the use of complementary image processing and analysis routines to measure the curvature of morphologies within these monolayers. The introduction of cholesterol within the monolayers stabilizes domain branches which curl and elongated over time. Previously it was shown that domain morphologies evolve to stripes of equilibrium widths. We are currently investigating the distributions of curvatures within the monolayer morphologies and their use as a signature of equilibrium behavior. |
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N00.00269: Simulation and Characterization of Pure RNA condensates Dilimulati Aierken, Jerelle Joseph It is known that pure RNA systems phase separate both in vitro and within cells. Several neurological and neuromuscular disorders are related to RNA-based condensates. However, it is still challenging to characterize microscopic dynamics and morphology of RNA condensates. To investigate the biophysical principles governing RNA condensation, we have implemented and optimized a coarse-grained model for studying RNA structure and phase behavior. Our approach not only reproduces key experimental findings on RNA–RNA phase separation but importantly we achieve multifold speed up in the simulation time compared to the state-of-the-art. With this efficiency, we study the long-time dynamics of RNA condensates as well as its dependency on primary sequences. Our study reveals the relationship between RNA physicochemical features and RNA condensation. Collectively, our work helps shed important insights on the material properties of pure RNA condensates. |
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N00.00270: Uncovering Rules Governing Small Molecule Partitioning into Condensates through Simulation Alina Emelianova, Jerelle Joseph Understanding the rules governing the interactions between small molecules and biomolecular condensates is crucial for engineering effective therapeutics against condensate-related diseases. Previous studies have demonstrated that certain drugs selectively partition and concentrate within condensates, occasionally leading to their dissolution. In this work, we focus on physicochemical principles that govern the interactions between small molecules and condensates. We conducted all-atom explicit solvent molecular dynamics simulations of model condensates and small molecules. As model systems, we studied the interaction between phase-separating aromatic-rich peptides and small molecules with a variety of chemical structures. Notably, we have observed divergent partitioning tendencies among various small molecules. To reveal principles governing the partitioning of small molecules, we compute the potential of mean force between molecular components and inter-residue contact maps, as well as characterize the chemical makeup of individual drugs. Our data reveals that certain small molecules exploit high-affinity binding sites inside condensates, leading to their increased partitioning. Consequently, our study helps shed light on the rules that govern interactions between proteins in condensates and small organic molecules, which can be exploited for therapeutic design against condensate-associated diseases. |
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N00.00271: HP1α oligomeric state modulates Heterochromatin 3D organization: Insights from a polymer model Ramin Basir, Vinayak Vinayak, Vivek B Shenoy While our understanding of heterochromatin’s nanostructure and its role in gene silencing is evolving, it remains nuanced. In this study, we propose a polymer model of HP1α with multiple domains and chromatin at the nucleosome level. This model enabled a detailed exploration of chromatin architecture, revealing a unique nucleosome organization modulated by HP1α's oligomeric states. Specifically, HP1α monomers establish a distinct nucleosome spacing throughout the genome and this spacing becomes locally condensed upon HP1α dimerization. Verification via Förster resonance energy transfer (FRET) microscopy reaffirms our findings. Therefore, our findings provide pivotal insights into the mechanisms of heterochromatin formation and preservation. |
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N00.00272: Perturbing polymerization and nucleation of RAD51 recombinase in a stochastic lattice model Ali S Tabei, Sabryn Labenz, Blaine Williams, Jenna Heinen RAD51 plays a crucial role in the homologous recombination process. We have developed a stochastic Monte Carlo lattice model to study how perturbing different binding properties of RAD51 affects the polymerization of RAD51-RAD51 and its mutants in solution and the nucleation of RAD51 polymers on a single-stranded DNA. |
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N00.00273: Predicting the potential cell size limit prior to bacterial cell division Joydip Chaudhuri Bacterial cells exhibit a diverse range of shapes and sizes, often regulated by the bacterial cell wall, in conjunction with cytoskeletal proteins and internal turgor pressure. Unlike typical polymeric membranes, bacterial cell walls possess greater thickness and rigidity, allowing them to maintain cell shapes while withstanding significant turgor pressure. Our study introduces a theoretical framework to model the dynamics of growing cell walls, rooted in the principle of minimizing energy dissipation. Within a bacterial cell wall, dissipative forces arise from the incorporation of peptidoglycan (PG) strands, while driving forces stem from changes in mechanochemical energy associated with maintaining wall shape. The interplay between mechanical and chemical energy offers insight into cell wall growth dynamics and provides a means to predict the maximum size of bacterial cells prior to cell division. Remarkably, our analysis, employing linear stability techniques on a typical system, closely matches the phase diagram obtained from numerical analysis of the full nonlinear theory. Nonetheless, the molecular intricacies of cell wall composition are still challenging, and we anticipate that a more precise constitutive model will yield even more accurate quantitative results. |
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N00.00274: Control of organ shape development by cellular mechanical properties Loann Collet, Sylvia R Silveira, Luc Lapierre, Agnieszka Bagniewska-Zadworna, Mohammad S Haque, Richard S Smith, Frederick P Gosselin, Daniel Kierzkowski, Anne-Lise Routier-Kierzkowska
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N00.00275: A computational study of the shear response and fracture resistance of the cytoskeleton of the single-celled organism Stentor Hunter Heineman, Soumik Mitra, Wallace F Marshall, Sindy Tang, Moumita Das Creating synthetic systems that mimic life is a captivating research frontier. Yet, current synthetic cell studies overlook a key feature of life: resilience to physical damage. We probe the biomechanical defense mechanisms of the single-celled organism, Stentor, known for its ability to resist and rapidly heal from mechanical wounds. Here we focus on the Stentor's cytoskeleton, the polymeric scaffolding crucial for its integrity and rigidity. Based on Stentor electron microscopy images, we model its cytoskeleton as a composite network: parallel microtubule bundles (KM fibers) integrated with an underlying network that offers transverse connections and contractile elements (myonemes) that facilitate contraction of the KM fibers. We characterize the mechanical response of this network by calculating the shear modulus, fracture resistance, and spatial distribution of stresses for various densities and stiffnesses of KM fibers and the densities of myonemes. Our results shed light on potential cellular wound resilience mechanisms and suggest design principles for robust synthetic cells. |
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N00.00276: Microscale Analysis of Brain Tissue Interaction with Microwave Radiation Denis Tonini In this work, we studied the effects of electromagnetic fields on biological matter at a micrometer distance. The objective is to estimate and compute the induced electric and magnetic fields within biological, using finite element modeling (FEM) software to analytically quantify the effects and resonances at a wide spectrum of frequencies. Our findings reveal that, within the model considered for sub-THz frequencies, electromagnetic waves induce resonance in micrometer-sized tissue, with the field reaching its peak within the biological substance. This insight is used for determining the effect of microwave radiation on induced electric and magnetic fields in the context of both brain stimulation applications and brain sensing. Consequently, the interaction between gray matter tissue and microwave radiation is studied to verify the feasibility and the power density requirements of arrays of nanomagnetic devices to stimulate neuron cells within approximately 100 µm distance. It is well-established that GHz frequencies can exert and promote inhibitory effects on synapses and suppress brains signals similarly to nano-pulsed electric fields. In this study, we utilized a FEM software to estimate the interaction of the electromagnetic field with specifically gray matter carefully controlling various parameters within the comprehensive model to quantify the effects on a micrometer scale in terms of the induced electric and magnetic field from a microwave source. We also calculate the specific absorption ratio (SAR) for different frequencies ranging from MHz to GHz to examine the magnitude of the effects and their implications on bioheating models. |
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N00.00277: Mechanically-driven closure of extreme membrane wounds in a single cell Kevin Zhang, Ambika Nadkarni, Martín Koch, Wallace F Marshall, Sindy Tang Wound healing is a fundamental aspect of living systems and is increasingly recognized in single cells. However, our understanding of single-cell wound healing is limited as many cell types used in prior studies cannot survive wounds larger than a few percent of the cell membrane area. In contrast, the giant single-celled ciliate Stentor coeruleus is a unique model that can robustly heal and regenerate from drastic wounds. Here, we study the interplay of wound healing capacity, wound size, and cell size in Stentor. Remarkably, at all cell sizes tested, Stentor easily survives wounds up to 60% of the cell membrane area, larger than any wounds reported in other single-cell models. This critical wound size corresponds to the geometric limit where the intact membrane area equals the minimum area needed to cover the cell volume (i.e., that of a sphere). In contrast to prior studies that only reported local wound healing events, we observe large-scale wrapping of intact cell membrane at a rate of ~100 – 500 μm2/s to aid in wound closure. We then show membrane wrapping is driven by KM fiber extension and/or myoneme contraction. Our work highlights how single cells can act as mechanical systems to enable large-scale cell functions. |
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N00.00278: Creasing as a candidate mechanism of foveal pit formation Tyler A Engstrom, Indigo S Peppard, Emily Chown, Dylan Mendoza Creasing is a phenomenon observed in hyperelastic materials and is characterized by sharply localized surface deformations that appear at ~35% compressive strain. The foveal pits of anoles (small iguanian lizards) are funnel-shaped and resemble creases when cut along the central axis. Furthermore, during foveal pit formation the anole eye contracts around 35% along this same axis [1]. We investigate creasing in synthetic retina-like geometries using (i) everted hemispherically capped tubes that extend recent experiments with uncapped tubes [2], and (ii) a vacuum apparatus that allows for curing a small puddle of elastomer in a pre-tensioned elastomer bowl. The latter experiment directly tests a recent hypothesis that a reduction in intraocular pressure drives foveal pit formation, and that an observed localized retinal mounding may also be implicated [1]. Our experimental results include features reminiscent of both foveal pits and visual streaks, and may lead to a better understanding of retinal morphogenesis under both normal and pathological conditions. |
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N00.00279: Exploring the Biointerfaces: Ab Initio Investigation of Nano-Montmorillonite Clay, and its Interaction with RGD Molecules Deniz Cakir, Warnakulasuriya Ashan Fernando In our study, we explored how a clay surface modified with Fe and Mg interacts with various RGD molecules. We found specific RGDs that strongly attach to the clay surface. Our calculations showed that the amino group in RGD plays a crucial role in this attachment, suggesting a way to design RGD for clay-based materials. Our calculations established several structural properties that are required to realize strong binding on the surface, including a number of -NH groups and steric effects. Strong binding is crucial since clay strongly binds RGD peptides, prevents detachment, and promotes cell adhesion and migration Additionally, our simulations confirmed that the clay-RGD systems remain stable under ambient conditions. |
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N00.00280: The Synthesis, Characterization, and Biocompatible Study of Boron Nitride Dots Raksha FNU
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N00.00281: Quantifying Microbial Transcriptomic Response to Antimicrobial Nanostructured Surfaces Allison Hohreiter, Bum-Joon Jung, Ralu Divan, Supratik Guha, Anindita Basu Antimicrobial nanostructures (AMNs) can be nanofabricated on surfaces to deter microbial colonization or biofouling. This is of interest for manufactured surfaces that frequently come in contact with biological matter, ex. implants. Our understanding of the mechanisms underlying microbe-AMN interactions has so far been largely sterile, with studies oftentimes modeling interfacial energy and material properties to estimate the forces at play. However, these approaches have not accounted for microbial response to the AMN stimulus, which has yet to be well quantified and may influence the outcome of the microbe-AMN interaction, ex. cell death or survival. To examine the microbial stress response to AMN stimulus, we have applied S. cerevisiae and C. albicans to antimicrobial black silicon nanoneedle surfaces and analyzed their transcriptomic response. |
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N00.00282: DNA Origami Motifs for Fast Localized Communication Mathew O Ogieva, Sebastian Sensale Over the past decades, dynamic DNA origami structures have emerged as promising candidates for nanoscale signal and cargo transport. Despite relatively fast diffusion rates, these structures face limitations in communication speed due to the reaction-limited nature of strand exchange mechanisms used for signal and cargo transfer. In this study, we explore how spatial confinement can expedite communication among DNA walkers and compare two potential mechanisms: one that constrains molecular motion to pseudo-rotational dynamics, and another that confines it to pseudo-linear dynamics. Using stochastic theories, we suggest that a combination of both mechanisms yields the highest velocity enhancement. This study offers novel insights into leveraging structural motifs to optimize signal propagation rates, with implications for sensing and computing applications in reaction-diffusion systems. |
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N00.00283: Supracellular Actin Network Remodeling During the Jamming Transition in Pseudostratified Epithelia Revi Brown, Jennifer Mitchel The tight regulation of the transition between stationary and migratory states is crucial to the proper functioning of epithelial cells during both homeostasis and pathological processes. The study of phase transitions in tissues provides insight into the underlying mechanisms of cellular movement. Recently, several biological tissues have been found to undergo jamming transitions, analogous to those previously described in soft matter particle physics. Human bronchial epithelial cells (HBECs) are a key model system for studying the biological jamming transition, having been shown to transition between a fluid-like unjammed state in which the cellular collective freely remodels, and a solid-like jammed state where motion is arrested. Previous cell culture work found that as basal stem cells differentiate to form a mature epithelium, the cellular collective slows, the shapes of individual cells became more rounded and less variable, as predicted by vertex models, and the tissue undergoes a jamming transition. However, the differentiating HBEC layer exhibits a complex, pseudostratified architecture which has not been accounted for in the models or analysis of collective behavior. Here, through the combination of live imaging and immunohistochemistry, we show that a multicellular dynamical change in HBECs is accompanied by supracellular structural changes in the actin cytoskeleton. As cells jam, the apical actin network percolates across the cell layer, leading to a rigidity transition. These findings provide preliminary evidence of a percolation transition in pseudostratified epithelia by characterizing the connection between multicellular dynamics and structural changes. |
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N00.00284: Active matter invasion and morphogenesis Haoran Xu, Mehrana R Nejad, Julia Yeomans, Yilin Wu Interaction between active materials and the boundaries of geometrical confinement is key to many emergent phenomena in active systems. For living active matter consisting of animal cells or motile bacteria, the confinement boundary is often a deformable interface, and it has been unclear how activity-induced interface dynamics might lead to morphogenesis and pattern formation. Here we studied the evolution of bacterial active matter confined by a deformable boundary. We discovered that an ordered morphological pattern emerged at the interface characterized by periodically-spaced interfacial protrusions; behind the interfacial protrusions, bacterial swimmers self-organized into multicellular clusters displaying +1/2 nematic defects. Subsequently, a hierarchical sequence of transitions from interfacial protrusions to creeping branches allowed the bacterial active drop to rapidly invade surrounding space with a striking self-similar branch pattern. We found that this interface patterning is geometrically controlled by the local curvature of the interface, a phenomenon we denote as collective curvature sensing. Using a continuum active model, we revealed that the collective curvature sensing arises from enhanced active stresses near high-curvature regions, with the active length scale setting the characteristic distance between the interfacial protrusions. Our findings reveal a protrusion-to-branch transition as a unique mode of active matter invasion and suggest a new strategy to engineer pattern formation of active materials. |
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N00.00285: Collectively moving filaments in oil suspensions of the nematode T. aceti Alyssa Agarie, Anton Peshkov Previous research indicates that the nematoda Turbatrix aceti, commonly known as vinegar eels, can synchronize their body oscillations under favorable conditions, such as the droplet's contact angle ( θ > 68°) to produce metachronal waves similar to the one that sports fans create on the stadiums. It is unknown whether these nematodes can still synchronize their motion in high viscosity fluids. We study the collective motion of nematodes in oils of different molecular weight and viscosity. We find that contrary to the water suspensions, nematodes in oil form collectively propagating filaments. We measure the oscillation frequency inside and outside the oil, the number of filament splits, the density of nematodes per region, and how fast the filaments are advancing. We find that the nematodes in less viscous oils were able to spread out faster and create interlocking filaments. In comparison, nematodes in more viscous oils only spread individually without creating collectively moving filaments. Their travel distance was smaller than the one of collective filaments in low viscosity oil. Further research is necessary to determine whether other factors such as oil density may have contributed to the results. |
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N00.00286: Localized Fluctuations of Microscopic Active Particles in Living Cells Johanna Harding, Simin Xia, Chong Shen, H Daniel Ou-Yang Microscopic active particles move through a combination of thermal Brownian motion and self propulsion. Brownian motion is of interest to researchers of drug delivery, algae growth, and nanotechnology. Experiments to understand active Brownian motion can have trouble knowing how to analyze the data they have, leading to the necessity of simulation. |
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N00.00287: Geometric Control of Cytoplasmic Streaming in the Drosophila Oocyte Olenka Jain, Michael J Shelley, Stanislav Y Shvartsman, Brato Chakrabarti, Reza Farhadifar This work probes the role of geometry in orienting self-organized fluid flows in the late stage Drosophila oocyte. Recent work has shown that a theoretical model, which relies only on hydrodynamic interactions of flexible, cortically anchored microtubules (MTs) and the mechanical loads from kinesin motors moving upon them, is sufficient to generate observed flows. While the emergence of flows has been computationally studied in spheres, actual late-stage oocytes are ellipsoidal. |
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N00.00288: Encapsulated bacteria deform lipid vesicles into flagellated swimmers Lucas Le Nagard, Aidan T Brown, Angela Dawson, Vincent A Martinez, Wilson Poon, Margarita Staykova We study a synthetic system of motile Escherichia coli bacteria encapsulated inside giant lipid vesicles. Forces exerted by the bacteria on the inner side of the membrane are sufficient to extrude membrane tubes filled with one or several bacteria. We show that a physical coupling between the membrane tube and the flagella of the enclosed cells transforms the tube into an effective helical flagellum propelling the vesicle. We develop a simple theoretical model to estimate the propulsive force from the speed of the vesicles and demonstrate the good efficiency of this coupling mechanism. Together, these results point to design principles for conferring motility to synthetic cells. |
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N00.00289: Material properties alteration by bacterial active matter Chenxi LIU Active matter, characterized by its inherent non-equilibrium nature, possesses the capacity to transfer energy from individual units to the surrounding environment. Recent work on active suspensions has demonstrated the potential of active units modifying passive material properties. In this study, we present experimental evidence illustrating how bacterial activity controls the dynamics of a binary mixture, leading to substantial changes in material properties. |
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N00.00290: Harnessing the collective motion of the nematode T. aceti to produce work Ashley L Robinson We are experimentally studying the possibility of displacing objects or producing fluid flows using the collective motion of the nematode Turbatrix Aceti, also known as the Vinegar Eel. It has previously been found that under favorable conditions, such as the droplet's contact angle ( θ > 68°), T. aceti can produce synchronously beating and moving metachronal waves. It has been observed that this collective motion can both exert a force on the border of the droplet and produce fluid flows inside the droplet. We want to harness these forces and flows to displace objects and generate on demand fluid flows. For the first goal we use 3d printed wedge shaped micro-boats with various angles of the wedge. For the second goal, we 3d print michrochannels with triangularly shaped pockets of various angles. We measure the displacement of the boats and the fluid flows produced in michrochannels as a function of the angle of the wedge and pockets. These experiments expand our knowledge on how active matter can be used both for the displacement of objects and generation of fluid flows. |
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N00.00291: Collective motion of confined bristle-bots Shalom Salvi, Enkeleida Lushi Collective motion, a phenomenon commonly found in nature and artificial systems, refers to the behavior of a group of individuals or agents, each moving independently, and arises due to the interactions of these 'active agents' with each-other and the surrounding environment. The resulting collective behavior is non-trivial and difficult to understand, let alone predict, especially in complex geometries. Understanding the effects confinement has on the emerging collective motion of active agents has thus become a central topic of research, and moreover can help to devise strategies to control and direct this motion for use in future technologies. We present experiments and computational studies of the collective motion of confined self-propelling agents realized by bristle-bots. We show that the emerging collective motion can be affected by the active agent's shape, their density, and the size and shape of the confining geometry. |
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N00.00292: Microtubule exciton polaron thermodynamic properties and dynamics NGANFO YIFOUE WILLY ANISET
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N00.00293: Emergent chirality in bacterial active suspensions Youhan XU, Yilin Wu Chirality is a ubiquitous phenomenon in nature spanning from molecular scale to galactic scale, such as the helical structure of DNA strands to the spiral shape of galaxies. Bacterial populations consisting of a large number of cells may also develop chiral structures due to microscopic chirality at the single cell level. Here we study the the emergence of chiral structures in bacterial suspensions arising from spontaneous chiral symmetry breaking in the collective motion of cells. Our study may offer a deeper understanding of bacterial self-organization and provide new insight to the self-assembly of living materials. |
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N00.00294: Signatures of energy dissipation in bacterial chemotaxis signaling pathways Qiwei Yu, David Hathcock, Yuhai Tu Chemotaxis signaling pathways in Escherichia coli are driven out of equilibrium by ATP hydrolysis, which enables the phosphorylation of regulator proteins that carry signals from the chemoreceptors to the motors. We show that recent experimental measurements of kinase activity exhibit signatures of this underlying energy dissipation. First, changes in receptor methylation shift kinase response curves over a disproportionately large range of ligand concentration, two orders of magnitude larger than the corresponding shift in ligand binding curves. Second, cells can spontaneously switch between active and inactive states, but the switch to inactivity takes longer, signifying time-reversal symmetry-breaking. In each case, we show that these measurements are inconsistent with equilibrium mechanisms. We develop non-equilibrium allosteric and lattice models that explain the microscopic origins of these behaviors and allow us to explore how they emerge as the system is tuned out of equilibrium. Our results indicate that strong dissipative driving plays a key role in enhancing signal fidelity and the range of adaptation in E. coli. |
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N00.00295: Growth dynamics of bacterial active fluids Ruizhi Zhao Living cells provide the primary systems for active matter research. While biologists have long studied the problem of growth and division in living systems, these processes are often overlooked in studies of living active matter. Here we study how growth dynamics may affect the collective motion and self-organization of active matter. The results may deepen the understanding of microbial dispersal and range expansion. |
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N00.00296: Integration of silicon chip microstructures in soft microfluidic device for in-line microbial cell lysis and characterization Anindita Basu, Supratik Guha, Allison Hohreiter, Bum-Joon Jung, Sunny Taylor Recent advances enable single-cell genomics in human tissues to identify constituent cell types and their functions. However, this technology has largely failed to translate to microbes that include fungi, bacteria, etc. and the microbiomes they constitute. There is no rapid, high-throughput technique that can be applied to multiple microbial species in an unbiased way. We aim to perform scRNA-seq of the microbiome to detect the constituent species, along with their genomic and biochemical activity. We developed a Silicon Chip-Integrated Soft Microfluidics (SCISM) platform to perform lysis of microbial cells rapidly and efficiently using micromechanical impact and demonstrated it on Saccharomyces cerevisiae and Candida albicans. As next step, we are integrating optical spectroscopy on the SCISM platform to characterize the cells and their lysates, to be compared with RNA-seq data. |
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N00.00297: Exploring single-cell heterogeneity in a developing biofilm Diana S Valverde Mendez, Jung-Shen Benny B Tai, Kee Myoung Nam, Japinder Nijjer, Jing Yan Biofilms consist of surface-associated bacteria embedded in an extracellular polymeric matrix. This matrix provides protection and allows for resource exchange within the community. Although bacterial colonies are known to exhibit broad levels of heterogeneity, it is not well understood how this extends to biofilms. It is largely unknown whether individual cells display phenotypic heterogeneity and how such heterogeneities affect the biofilm’s life cycle. We use the model organism Vibrio cholerae to study spatiotemporal patterning within biofilms, as well as heterogeneities in gene expression and second-messenger molecule concentrations at the single-cell level. Combining high-resolution time-lapse imaging and fluorescent reporters, we find multiple heterogeneities on developing biofilms grown from single cells. We observe variable expression levels in relevant biofilm genes, including matrix production and quorum sensing. We also see differences in c-di-GMP concentrations (a second-messenger molecule that regulates the cell’s transition from motile to sessile) across cells in the biofilm. These heterogeneities are coupled to the cells’ mechanical environment and their structural organization, exemplifying how variations on biofilm regulation, cell organization and local mechanical environments are correlated in the biofilm development process. We also show progress towards understanding the role of inheritance by tracking single-cells in a growing biofilm. |
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N00.00298: Studying Motor-Free Motility in Synthetic Cells Laura CASAS FERRER, LEI XIANGTING, JERRY HONTS, Saad Bhamla Ciliated protists are single celled eukaryotic organisms with a striking particularity – some of them display the fastest motions in the biological world! The mechanism that enables such phenomenon is a motor-free, calcium-based cytoskeletal system. Unlike the actin-myosin based cytoskeletons, ATP is not directly consumed; a local increase in cytosolic Ca2+ concentration is what triggers the contraction. In this project, we aim to study the mechanical effects of calcium-based motor-free contraction in the cellular membrane, and how the interplay between these two elements allows cell motility. |
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N00.00299: Development and functionality control of liquid canals in a bacterial community Qihui Hou, Shiqi LIU, Yilin Wu Long-range material transport is essential to supply water, nutrients, and oxygen in animals and plants. By contrast, material transport in bacterial community is often carried out by molecular diffusion, and is often short-range, with low efficiency over longer ranges. In the previous study, we reported a unique form of rhamnolipids-driven long-range directed canals for material transport in Pseudomonas aeruginosa communities. Here we use genetic manipulation to further understand and control the development and functionality of liquid canals spatially and temporally. The study may provide insight to engineering living materials and synthetic microbiota. |
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N00.00300: A Schr"{o}dinger Equation for Evolutionary Dynamics Trung V Phan, Vi D Ao, Duy V Tran, Kien T Phan, Duc M Nguyen, Huy D Tran, Tuan K Do, Van H Do We establish an analogy between the Fokker-Planck equation describing evolutionary landscape dynamics and the Schr"{o}dinger equation which characterizes quantum mechanical particles, showing how a population with multiple genetic traits evolves analogously to a wavefunction under a multi-dimensional energy potential in imaginary time. Furthermore, we discover within this analogy that the stationary population distribution on the landscape corresponds exactly to the ground-state wavefunction. This mathematical equivalence grants entry to a wide range of analytical tools developed by the quantum mechanics community, such as the Rayleigh-Ritz variational method and the Rayleigh-Schr"{o}dinger perturbation theory, allowing us to not only make reasonable quantitative assessments but also explore fundamental biological inquiries. We demonstrate the effectiveness of these tools by estimating the population success on landscapes where precise answers are elusive, and unveiling the ecological consequences of stress-induced mutagenesis -- a prevalent evolutionary mechanism in pathogenic and neoplastic systems. We show that, even in a unchanging environment, a sharp mutational burst resulting from stress can always be advantageous, while a gradual increase only enhances population size when the number of relevant evolving traits is limited. Our interdisciplinary approach offers novel insights, opening up new avenues for deeper understanding and predictive capability regarding the complex dynamics of evolving populations. |
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N00.00301: Title: Self-organized criticality explains the emergence of irregular vegetation patterns in semi-arid regionsOral: Malbor Asllani Vegetation patterns in semi-arid areas manifest either through regular or irregular vegetation patches separated by bare ground. Of particular interest are the latter structures, that exhibit a distinctive power-law distribution of patch sizes. While a Turing-like instability mechanism can explain the formation of regular patterns, the emergence of irregular ones still lacks a clear understanding. To fill this gap, we present a novel self-organizing criticality mechanism driving the emergence of irregular vegetation patterns in semi-arid landscapes. The model integrates essential ecological principles, emphasizing positive interactions and limited resources. It consists of a single-species evolution equation with an Allee-logistic reaction term and a nonlinear diffusion one accounting for self-segregation. The model captures an initial mass decrease due to resource scarcity, reaching a predictable threshold. Beyond this threshold and due to local positive interactions that promote cooperation, vegetation self-segregates into distinct clusters. Numerical investigations show that the distribution of cluster sizes obeys a power law with an exponential cutoff, in accordance with empirical observations found in the literature. The study aims to establish a foundation for understanding self-organizing criticality in vegetation patterns, advancing the understanding of ecological pattern formation. |
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N00.00302: Pattern Formation in Mathematical Billiards with Spatial Memory Thijs Albers, Stijn Delnoij, Nico Schramma, Maziyar Jalaal Many classes of active matter develop spatial memory by encoding information in space, leading to complex kernels further (arXiv:2307.01734). |
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N00.00303: Nonlinear traveling wave instability and arrested coarsening in a model for protein patterns on biomembranes Benjamin Winkler, Sergio A Muñoz, Markus Bär
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N00.00304: Quantifying cross-species primate facial cues Felipe Parodi, Jordan K Matelsky, Michael L Platt, Konrad P Kording Faces are central to primate social communication, encapsulating emotions, social cues, and individual identities. The advent of deep learning has heralded a new era for robust, high-throughput video-based facial analysis; however, non-human primates present unique challenges due to morphological variability and environmental complexities. To overcome these challenges, we need a dataset devoted to cross-species primate faces to train deep learning models for high-throughput face analysis. Here, we introduce PrimateFace, the first large-scale, cross-species dataset of primate images, annotated with face bounding boxes and facial landmarks, capturing a diverse array of settings, facial expressions, developmental stages, and social interactions. Of the 500,000 images, 5,000 of these images are further annotated for face recognition and facial action units. Using a self-supervised approach, we first pretrained models on unlabeled PrimateFace images, then fine-tuned the representations on smaller annotated subsets for supervised facial analysis tasks. We contribute trained notebook tutorials with fine-tuned transformer and light-weight architectures, including the self-supervised DINO and efficient MobileViT architectures, demonstrating competitive performance and generalizability across primate species and tasks. PrimateFace opens new avenues for cross-species facial analysis and opportunities to study primate social cognition. |
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N00.00305: The Role of hubs and Authorities Nodes on the Emergency of synchronization on a Neurological Complex Network Jonas F De Oliveira, Epaminondas Rosa, Rosangela Follmann, Celso V Abud, Elbert E Macau Epilepsy is a neural disorder related to intense synchronous neural activities due to increased blood flow in the cerebral cortex, causing seizures followed by fainting. Antiepileptic drugs can prevent seizures and fend off the emergence of synchrony in neural networks. However, about a third of medicated patients experience seizures again. Thus, the urge to comprehend brain dynamics and to provide a better quality of life for people with this condition motivates several scientific efforts. To this end, we modeled a feline`s cerebral cortex as a complex network. Therefore, the objective is to investigate the most influential areas of the cerebral cortex and how they influence the dynamics of synchronization associated with epilepsy. To study synchronization, the Kuramoto model was used to govern the dynamics between the areas of the cortex. We used the Hypertext Induced Topic Search (HITS) algorithm to classify internet pages and to identify the most influential nodes in the feline cerebral cortex network. Regarding the dynamics and measures of global, mesoscopic, and microscopic synchrony, results were obtained for a scenario using the original network and two other scenarios, in which it was considered a disturbance, to simulate the action of an antiepileptic drug, the disturbance reduced the intensity of connections of a group containing random nodes and the group with nodes chosen by the HITS algorithm by 50%. Finally, the applied disturbance lagged the network’s global, microscopic, and mesoscopic levels. For future works, we aim to investigate the cat’s neural network using more sophisticated and realistic dynamics given by a Hodgkin-Huxley-type neuron. |
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N00.00306: Motion estimation from optical flow using camera mimicking blowfly visual processing Hannah Kramer, Charles Edelson, Sima Setayeshgar, Robert de Ruyter Optical flow, the apparent motion of spatially varying intensity profiles produced by a moving observer, allows estimation of self-motion and is used by many organisms for locomotion through their natural environment. However, the details of how this is accomplished using visual signals derived from dynamic natural scenery is unknown. In this work, we computationally investigate this problem using natural stimuli recorded using a specially designed "FlEye" camera that mimics the blowfly (Calliphora vicina) visual system and is equipped with joint gyroscope and accelerometer to capture motion trajectories. We use the convective derivative of the filtered image intensities to obtain one- and two-dimensional estimators of wide-field motion. Comparing yaw rate estimators from these two approaches, we demonstrate that the two-dimensional estimation provides a better determination and make connection with motion estimation in the blowfly visual system. |
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N00.00307: A Comprehensive Metric Unveils Unstable Points in a Motor Program for Song Generation in Birdsong Jorge M Mendez, Brenton Cooper, Franz Goller The acquisition of an acoustic template is a fundamental component of vocal learning. In the absence of a model, birds fail to develop species typical songs. In zebra finches (Taeniopygia guttata), tutored birds produce songs with a stereotyped sequence of distinct acoustic elements, or notes, which form the song motif. Songs of untutored individuals feature atypical acoustic and temporal structure, including repetitions of sound elements. Here we studied songs and associated respiratory patterns of tutored and untutored male zebra finches to investigate whether similar acoustic notes influence the sequence of song elements. A subgroup of untutored animals developed songs with multiple acoustically similar notes that are produced with alike respiratory motor gestures. These birds also showed increased syntactic variability in their crystallized motif. Sequence variability was associated with the presence of song elements which showed high similarity in acoustic structure and underlying respiratory motor gestures. The results of this study indicate that the note is a fundamental acoustic unit in the organization of the motif and the neural code for song syntax. |
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N00.00308: Nonequilibrium adaptation and phenotypic switching to big environmental changes, like booms and busts Ying-Jen Yang, Charles D Kocher, Ken A Dill In statistical physics, systems can exchange energy or matter with baths that provide fixed resources. But, in biological evolution, systems face highly fluctuating environments, including those that undergo booms and busts. The ability to sense the environment and adapt are thus the key for the system to thrive. We make the simplest possible model of an adaptive process: a binary sensor in a stochastic two-state (boom or bust) environment. Our goal is to identify and analyze all essential parameters that characterize this system's adaptation to its environment. We first show analytically that the total system must be out of equilibrium for the sensor to outperform a random oscillator. A novel relation among the system's sensing performance, the environment changing rate, and the level of nonequilibrium is derived. We then analytically find the optimal sensor when the system's adaptation rates are bounded by their physical limits. Lastly, we generalize our results above to describe the interplay between phenotype switching and population growth under a stochastic boom-bust environment. |
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N00.00309: Exploring Latch-Mediated Spring Actuation Work Multiplication Principles with a Slingshot Spider Bioinspired Robotic Mechanism James Clinton, Ella C Allgor, Audrey L Gruian, Ria L Haapala, Elena D Korn, Erin L Wang, Mark Ilton Latch-mediated spring actuation (LaMSA) is used to power biological and engineered systems beyond the power limits of motors. LaMSA systems use a spring to store potential energy, lock the spring in place using a latch, then release the latch to control the rapid release of the spring's energy. The concept of work multiplication, primarily found in engineered LaMSA systems, enables extreme performance by using multiple strokes of a motor to load a spring. Slingshot spiders are a biological example of a work multiplication LaMSA system. They load conical webs using multiple strokes of their legs to store and release spring energy to capture flying insects. We present a slingshot spider inspired mechanism to explore properties of work multiplication systems. We discuss broader aims for the project; understanding control mechanisms and strategies for LaMSA systems, establishing links between material and geometric properties of web-springs and elastic performance, and determining scaling relationships for work multiplication systems under new scaling regimes. We present plans for addressing each of these broad aims using our proposed mechanism. Finally, we also present a preliminary prototype of the mechanism and preliminary experimental results for the prototype. |
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N00.00310: Robophysics-inspired experiments in canines to discover strategies for quadrupedal negotiation of regular obstacles Siya Damle, Michelle Joyce, Benjamin Doshna, Haodi Hu, Feifei Qian, Simon Wilshin, Andrew J Spence Just as four legged animals have provided inspiration for robotic technologies, robot experiments can inspire new questions in animal locomotion. This study continues research into how dogs handle a regular series of obstacles, inspired by past work that found that quadrupedal robots can have stable trajectories that depend systematically on the gait that they use when moving over obstacle arrays. Subsequently we examined dogs as they negotiated similar arrays of varied spacing. We found that the dogs did not display large changes in average gait, but did exhibit stride length that varied in proportion to obstacle spacing. Dogs appear to have further strategies to adapt to the obstacles, however, that we explore here: 1) they can accumulate error and then perform a "reset" step to correct themselves; and 2) the animals can zig-zag across the obstacle array, presumably to utilize a more "comfortable" stride length. We explore the parameters that may predict a "reset" step, including the canines' stride lengths and limb phases, and we further look for morphological or other properties of the animal that may predict zig-zag behavior. This study may shed light on behaviors for agile, stable, and/or economical quadrupedal locomotion over more varied terrain. |
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N00.00311: Failure-free jumping soft robot using elastic fiber inspired by Jumping nematode Sunny Kumar, Daehyun Choi, Summer Clark, Saad Bhamla Jumping nematodes utilize longitudinal muscles to store energy in their cross-fiber helical array tissue during curvature formation after buckling limit. This energy is rapidly released when the capillary bridge between contacts breaks. Drawing inspiration from this unique behavior of nematodes, a soft robot has been designed to emulate the nematode's physical properties. The nematode's cross-fiber helical tissue is mimicked using a McKibben structure made of elastic fibers. This structure is capable of storing elastic energy, even during buckling. To simulate the muscle contractions of Entomopathogenic Nematodes (EPNs), low-mass shape memory alloy actuators are employed. By applying an electric current to these actuators, muscle-like contractions are replicated. Additionally, a latch mechanism, created using 3D printing, is incorporated to swiftly release the stored elastic energy at peak contraction. The instantaneous velocities of these movements of the soft robot were calculated using high speed camera. Next, we analyzed several parameters such as the variation in robot length, curvature to which the soft robot prototype's shape deviates from its original state, as well as the relationship between stress and strain. This was achieved by testing the robot's compressibility and deformation. This research not only furthers the domain of soft robotics but also underscores the potential of bio-inspired design principles and advanced materials in the realm of robotic engineering. |
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N00.00312: CELLOIDS: towards cell-inspired autonomous microrobots Jyoti Sharma, Francesco Bianciardi, Dario Cecchi, Eugenia De Remigis, Hilda Gomez Bernal, Elisa L Petrocelli, Elisa Roberti, Gaia Petrucci, Stefano Palagi White blood cells can move inside soft tissues, squeezing through narrow gaps between cells. This is known as interstitial migration and relies on the adhesion-independent amoeboid locomotion of cells. Inspired by such cells, we aim at realizing untethered microrobots that are ultra-deformable and able to autonomously navigate soft body tissue following local cues. We refer to such microrobots as celloids. The ultra-soft microrobot body consists of a Giant Unilamellar Vesicle (GUV), a liquid droplet enclosed by a nanometer-thin lipid membrane. The GUV contains self-propelled Janus microparticles, which should lead to the amoeba-like deformation of the microrobot. Alternatively, the vesicle can be loaded with a magnetic ferrofluid to enable magnetic deformation and movement of the microrobots. Our ongoing research investigates microrobots’ behavior in porous hydrogel environments and their response to pH gradients. We perform numerical simulations (in Julia) employing active Brownian particles moving in curved confinements and found particles tend to accumulate at high curvatures. Our work in biomimetic microrobotics will potentially enable innovative solutions for precise drug delivery. |
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N00.00313: The Logistics of Plant Growth, Bridging the Gaps in Disparate Data - a Meta-Analysis Viraj Alimchandani, Elvis Branchini, Anne-Lise Routier Quantifying cell growth is essential for understanding the biophysics of development and unveiling the effects of gene expression at the cellular level. However in plant biology, the majority of growth data is disparate and lacks a coherent framework, making it difficult to compare growth rates at different scales, between organs, and across different studies. In our meta-analysis, we have extracted and analysed growth data at the organ and cellular scale from hundreds of studies over 30 years and proposed a mathematical framework for comparing growth between different organs across developmental stages and types of cell dynamics. Our analysis revealed that probing growth at the cellular scale during organ initiation is key to understanding later developmental stages that lead to the organ final size. By providing a map of cell and organ expansion in different organs of the model plant Arabidopsis thaliana, our work serves as a benchmark for experimentalists and modellers who need a reference point of organ growth in controlled conditions. We begin to bridge the gap between growth at the cellular and organ scales and expose the lack of data at the crucial early stages. Finally, the framework we established for converting and presenting growth rate data can be used in future studies to aid comparison with other works. |
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N00.00314: Physical Limits of Cell Migration Aravind Rao Karanam, Richa Karmakar, Dorsa Elmi, Wouter-Jan Rappel Chemotaxis, the motion of cells directed by chemical signals, is a multi-step process in eukaryotes: molecules of the chemoattractant activate the receptors on the cell surface, which triggers a cascade of reactions that ultimately results in the motion of the cell through membrane deformation. The ultimate speed of cell migration is determined by the rate limiting step of the process. Few studies have probed the limits of chemotaxis considered as a whole, though the limits of some individual processes are known. We measured the speeds of Dictyostelium cells in response to chemoattractant waves of controlled size and speed generated using microfluidic devices. We find that cells are able to consistently follow the wave for more than hundred times their size, and for about an hour, and that their speeds are significantly higher than the observed values in static gradients. We present a model describing the relationship between the cell speed and the wave speed and discuss its implications. |
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N00.00315: Mammalian sperm navigation within the female reprodutive tract Meisam Zaferani For successful fertilization in mammals, sperm must navigate the dynamic female reproductive tract, reaching the site where an egg is released and then fusing with it. During this journey, sperm employs various navigational mechanisms guided by biophysical and biochemical cues present in the tract. In this presentation, I explore how fluid flow, physical boundaries, ambient rheology, and tract chemicals act as cues, and promote a wide range of swimming behaviors in bovine sperm. I further discuss our experimental findings alongside theoretical models to interpret how sperm's response to these cues facilitates its navigation in various functional regions of the tract. |
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N00.00316: Effect of lithium isotopes on sodium/lithium/calcium exchanger in mitochondria Irina Bukhteeva, Fasih A Rahman, Brian Kendall, Robin Duncan, Joe Quadrilatero, Evgeny Pavlov, Michel J Gingras, Zoya Leonenko Lithium (Li) has been a primary treatment for bipolar disorder for decades, but its mechanism of action remains unclear. Li has two stable isotopes: 6Li and 7Li (natural abundances are 7.5% and 92.5%). These isotopes differ in mass and nuclear spin. Previous studies showed that Li isotopes have different effects on animal behaviour and on electrical response in neuronal tissues. To further investigate these effects, we focused on the sodium/lithium/calcium exchanger (NCLX) in mitochondria, which is a proposed target for Li+ ions. Mitochondria play a crucial role in calcium regulation, affecting synaptic transmission and neuronal signal processing. The study investigates Li isotopes at the single-channel level, potentially revealing quantum effects in ion transport. |
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N00.00317: A Minimal Model for Affinity Maturation and Vaccination Protocols Saeed Mahdisoltani, Pranav Murugan, Mehran Kardar, Arup K Chakraborty The adaptive immune system's ability to recognize previously unseen pathogens through affinity maturation is a remarkable biological inspiration. In light of this, we develop a minimal model focusing on B cells inhabiting a trait space that quantifies their affinity towards various strains of a mutating pathogen. The objective of an effective vaccination protocol is to guide and accelerate affinity maturation in order to optimize specific characteristics of the resulting B cell population, e.g., their neutralizing breadth. We explore this question using a simple linear stochastic birth-death-mutation model with varying levels of precision. We start with an analytical investigation of the mean-field model and utilize operator techniques and a path integral formulation to obtain qualitative features of the vaccination protocols that enhance the desired changes of the population within the trait space. Subsequently, we assess the validity of our mean-field predictions through stochastic simulations. |
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N00.00318: Glioma cells in vitro display liquid crystal characteristics Anna Argento, Syed M Faisal, Carles Blanch-Mercader, Pedro R Lowenstein Glioblastomas (GBM) are the most common adult brain tumors, characterized by rapid invasion into the normal brain and therapeutic resistance. We have previously shown that GBM tumors exhibit self-organized, nematically aligned, multicellular structures, termed "oncostreams," that influence tumor invasion and malignancy. To further understand oncostream dynamics and the biomechanical interactions between glioma cells and the ECM we established a novel in vitro system. Time-lapse imaging revealed the presence of topological defects in the GBM cultures. Two types of topological defects were mainly found in the system: comets (+1/2 charge) and trefoils (-1/2 charge). Our investigation of topological defects aims to reveal their potential functions within brain tumors related to cancer cell invasion, collective migration, and apoptosis. Our results show, on average, high levels of apoptosis within the trefoil defect core and at the head of comet defects. This also impacts local cell density, with about 40% fewer cells at the trefoil core compared to elsewhere in the culture. Future work aims to study this phenomenon in 3D, utilizing a gel platform to allow for the hypothesized migration upwards at defect sites. Our results demonstrate that glioma cells grown in vitro behave as liquid crystals. Our data will define novel physical functional structures in GBMs, leading to the development of therapeutic strategies targeting oncostreams and topological defects. |
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N00.00319: 13C NMR Investigation of the Metabolic Effects of Lanthanides in Neuroblastoma Cells Cody Larsen Lanthanides are commonly utilized as initial substances for creating contrast agents to enhance the signal intensity in magnetic resonance imaging (MRI). Nonetheless, many of these compounds are linked to cytotoxicity, necessitating the development of modified versions to mitigate their harmful effects. Similarly, paramagnetic transition metals have been investigated as MRI contrast agents, but with limited success. |
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N00.00320: Predicting Peptide Immunogenicity in Cancer Marcus Thomas Within the last decade there has been remarkable progress in cancer therapies based on utilizing a patient’s own immune system to recognize and target cancer cells. Unfortunately, cancer mutated peptides - neoantigens - often exist in an ambiguous space in terms of their immunological similarity to self (as characterized by the subset of MHC-presented epitopes from among the human proteome) and to non-self. Tumor vaccines in particular rely on the fact that immune cells can be taught to recognize neoantigens as non-self. This recognition process involves a number of separate molecular processes which, in aggregate, contribute to the evolutionary fitness of the clonal populations to which a neoantigen belongs. Primary among these processes are antigen presentation — MHC molecules associated with human leukocyte alleles (HLAs) present potentially foreign antigens to the immune system — and subsequent T-cell receptor (TCR) binding. We develop a neoantigen quality model by considering how immune tolerance, i.e., the natural suppression of TCRs that bind to immunologically-self peptides thereby preventing auto-immune reactions, affects their binding to presented neoantigens in the context of patient specific HLAs. Our new approach incorporates terms relating neoantigen-HLA pairs to the presented human proteome. These terms are combined in a thermodynamics inspired equation governing the binding dynamics of neoantigens and T-cell receptors. The overall fitness of a clonal population within a tumor depends on the contributions from every neoantigen, allowing a direct connection between accumulated mutations, the immune system and predictions of evolutionary trajectories. We present initial results illustrating the framework's ability to distinguish patient survival duration based on differential clone fitness. |
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N00.00321: Effects of Substrate Rigidity on Cancer Cell Membrane Tether Strength Probed Using Single Cell Force Spectroscopy Ching-Hwa Kiang, Sithara Wijeratne, Jingqiang Li, Tsung-Cheng Lin, Ian Lian, Nicolas Nikoloutsos, Raymond Fang, Kevin Jiang Investigating the interplay between substrate rigidity and cell mechanics offers insights into cell migration and proliferation, which is critical for understanding cancer progression. This study utilizes single-cell force spectroscopy to examine cancer cells on substrates with varying rigidities. The tether-breaking force, extracted from force-distance curves, is a critical metric for measuring membrane tether characteristics. Our results indicate increased tether force in response to substrate rigidity, plateauing at an asymptotic limit. Interestingly, this trend remains consistent across three distinct cancer cell lines, with the most significant shifts observed in regions mimicking softer tissues, hinting at a universal cancer cell mechanical response to substrate rigidity. |
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N00.00322: The effect of density-dependent infection on ODE models of viral dynamics Hana M Dobrovolny, Hope Sage Ordinary differential equation (ODE) models of viral infections assume that the components are spatially well-mixed. This is a particularly bad assumption at early times during the infection when high concentrations of virus are located near the few productively infectious cells. Density-dependent infection rates can help account for this spatial heterogeneity while maintaining the ODE framework. We explore the effect of incorporating three different density-dependent infection rates: the saturated incidence, the Beddington-DeAngelis, and the Crowley-Martin models. We characterize the effect of density-dependent infection by measuring a number of viral titer characteristics (peak viral load, time of peak, upslope, downslope, and infection duration), as well as the basic reproduction number and the infecting time. We find that larger density dependence tends to slow down the infection and lowers the basic reproduction number; consistent with the idea that spatial ``clumping'' of the virus early in the infection will limit its access to uninfected cells, slowing down the infection. |
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N00.00323: Computational cyclic peptide design against prion-induced toxicity Ioana M Ilie Prion diseases are neurodegenerative disorders associated with the conversion of the cellular prion protein (PrPC) into a pathologic conformer (PrPSc). |
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N00.00324: Pressure-Dependent Collapsibility of Proteins: The Impact of Topology and Length Jiayi Wang, Dave Thirumalai, Margaret S Cheung, Andrei G Gasic Many efforts have been made to find the physics that guides amino acid sequences to fold to their native structure. It has been shown that the “foldability” of a sequence is directly related to its “collapsibility”. Thus, studying the “collapsibility” of a sequence is essential to understand its folding. The theory of collapsibility [1] demonstrates that the propensity of a sequence to collapse is linked to the native state topology, implying that natural selection favors those sequences that are compact. In this study, we use pressure perturbation to interrogate this relation. We extended the model by taking into account the solvent-induced desolvation barrier and its pressure dependence. We show that while pressure denatures fully folded states, proteins still tend to collapse to a water-mediated state, with topology playing a dominant role in the pressure dependence of the process. Generally speaking, proteins with more non-local contact interactions are more sensitive to pressure. The average change in water-mediated enhances collapsibility in proteins with more longer-range interactions is significantly greater. This shows that as pressure increases, proteins with relatively longer-range interactions are more prone to changing to a water-mediated collapsed state. Our study generalizes the notion of collapsibility, and relates it to the dependence on topology, thus providing further insights into the pressure dependence of collapsibility. |
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N00.00325: Emergence of helicity in double-stranded semiflexible chains with interstrand interactions Ee Hou Yong, Farisan Dary Helicity is a fundamental feature of the building blocks of life, namely, DNA, RNA, and proteins. The emergence of helicity in biopolymers is related to the base-stacking interactions but the actual mechanism of helical formation is still not well understood. In this work, we demonstrate how a simple model of semiflexible polymers without latent capability of forming helices can adopt helical conformation via interstrand interactions. Our model consisting of two semiflexible chains dressed with steric effects and are being held together as they are subjected to thermal fluctuations. We regularize the helical handedness of the conformation by imposing a parity-symmetry breaking term. We perform Monte Carlo simulations to understand the statistical mechanics of our model and analyze the qualitative differences in the resulting conformation as the temperature and the model parameters are varied. |
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N00.00326: Trapping single amphitrichous magnetotactic bacteria in small compartments for flow imaging Paulo Chu Magnetotactic Bacteria (MTB) are unicellular microoxic organisms that align with magnetic field lines. They orient and swim along the Earth's magnetic field in search of favourable environments; this process is called magnetotaxis. One can take advantage of MTB’s magnetic properties by generating an external magnetic field to direct their motion. There are exciting applications for MTB in many fields, for example nanorobotics and nanomedicine. However, to take full advantage of this magnetic control opportunity, we need to know more about the propulsion mechanism of MTB. We are interested in one species of MTB, Magnetospirillum magneticum AMB-1, which are corkscrew-shaped and amphitrichous (having a flagellum on either pole). A flow field map has not yet been experimentally determined for amphitrichous bacteria. We have tested different entrapping methods to be able to image a single, genetically engineered fluorescent AMB-1 cell in a micron-sized pit together with fluorescent beads. This way, we can image and track the bacteria and reconstruct the flow field they generate using the beads and particle tracking velocimetry. We thus hope to answer questions about the respective roles of the leading and trailing flagella, as well as that of the corkscrew body, in propulsion. |
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N00.00327: Non-Optical, Label-free Imaging of Bacteria with Electrical Impedance Spectroscopy. Joseph T Incandela, Manar Abdelatty, Pushkaraj Joshi, Jacob Rosenstein, Joseph Larkin Optical imaging has provided insights into many fundamental aspects of bacterial colony growth, including expansion mechanisms, phenotypic pattern formation, and genotypic segregation. However using light to form images limits the range of environments and species we can investigate. Here we introduce a non-optical method to perform days-long timelapse imaging experiments on bacterial colonies over millimeter length scales in up to three dimensions. The method forms images by placing bacterial samples in contact with a transistor array that measures the electrical impedance of the material near each pixel. We demonstrate that impedance imaging can resolve spatial and temporal variation |
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N00.00328: Bacterial population inversion near a hydrodynamic blackhole Shengkai Li, Trung V Phan, Robert H Austin We present a 2-dimensional enclosed microfluidic environment that utilizes concentric rings of funnel ratchets which act like gravity to direct motile bacteria (E.coli) towards an exit hole, entry into which irreversibly sweeps the bacteria away via hydrodynamic flow. We show that the disappearance of bacteria and their signaling molecules near this hydrodynamic ``black hole'' triggers the emergence of a population inversion where the remaining bacteria collectively move away from the black hole in spite of the presence of increased nutrients within the flow stream and the effective gravity force field. We study the fundamental significance of cell-cell communication in these phenomena by simulating different Brenner-Patlak-Keller-Segel models including those with and without a direct intercellular information flow, through analytical and numerical approaches. This experiment reveals how local bacteria density and signaling chemicals allow bacteria to can gain global information about their surrounding, and collectively avoid a hydrodynamic event horizon. |
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N00.00329: Accurate estimation of translation rate parameters explains stoichiometric protein synthesis in E. coli Ajeet K Sharma E. coli has long served as a prominent model organism for exploring the fundamental principles of cellular and molecular genetics. Nevertheless, there remain unresolved questions surrounding the origins of certain experimental observations related to the regulation of gene expression in E. coli. One notable example is the production of multiprotein complexes where the synthesis of their essential subunits is proportional to their stoichiometry in the complex. In this study, we employ a combination of next-generation sequencing data and stochastic simulations of protein synthesis to elucidate the underlying mechanisms governing the proportional synthesis of proteins within these multicomponent complexes. Our findings reveal that the initiation rates for translating all subunits in these complexes are directly proportional to their stoichiometry, thereby establishing a constraint on protein synthesis kinetics that achieves proportionality without necessitating feedback mechanisms. Additionally, our research identifies that translation initiation rates in E. coli are impacted by factors such as coding sequence length and the prevalence of A and C nucleotides near the start codon. Consequently, this investigation rationalizes the significance of conserved and nonrandom gene features in dictating translation kinetics, unveiling a pivotal principle in the regulation of protein synthesis. |
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N00.00330: Bacterial Growth Dynamics at Fluid-granular Interfaces Shanen Arellano, Raymond R Copeland, Peter Yunker Bacteria in nature often live in both unconstrained fluid environments and in spatially-constrained granular media. Previous studies show that bacteria exhibit different growth and competitive dynamics than what is observed in unconstrained environments. These studies are typically conducted in artificially created spaces, such as microfluidic devices, which feature highly simplified geometries. However, in nature, bacteria often have the ability to move from one environment to another, such as from the sand at the bottom of a pond into the water above, or vice versa. Therefore, we aim to investigate how bacterial growth proceeds in environments that replicate the highly heterogeneous geometries they confront in nature. To do so, we created a lab-controlled environment that features a column of unconstrained fluid over a pile of granular materials, which creates an environment where living space, nutrients, and movement are limited. We utilize a fluorescent strain of E. coli to observe growth dynamics. We observe the bacteria on micro- and macro-scales using microscopy and microbiology lab techniques. We found that when given the option of unconstrained fluid and highly constrained granular materials, our E. coli strain preferentially attaches to granular media. As a result, they fail to utilize all the nutrients in their environment and thus grow less in the presence of rather than in the absence of granular media. We find that bacteria in the presence of granular materials grow to at most 70% of the size of a population grown with the same amount of growth media but without granular materials. Furthermore, we found that cells are resistant to mechanical shearing (shaking) and viscous forces implying that cells adhere to the granular material by self imposed forces despite the presence of abundant nutrients available elsewhere. |
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N00.00331: Sum Frequency Generation Vibrational Spectroscopy and Imaging of Crystalline Cellulose Microfibrils in Plant Cell Walls Juseok Choi, Seong H Kim In plant cell walls, cellulose microfibrils (CMFs), which are bundles of cellulose, are the key load-bearing components that are mixed with other matrix polymers to carry specific mechanical properties necessary to fulfill their functional roles. However, due to the structural complexity of plant cell walls, characterizing CMFs without interference from other components is significantly challenging. Sum frequency generation (SFG) vibrational spectroscopy has the capability to selectively characterize crystalline (noncentrosymmetric) materials dispersed in a three-dimensional amorphous medium due to its unique selection rules. |
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N00.00332: Analysis of a model of biomolecular interaction for small separations at the Debye-Hückel level Timothy P Doerr, Oleg I Obolensky, Yi-Kuo YU The cellular environment, which in fact is a dense collection of biomolecules in a high dielectric constant solvent (water) containing various ions, can in certain respects be modeled as a colloidal system. Previous work has focused on rigorously examining at the Debye-Hückel level an arbitrary collection of dielectric spheres in a high dielectric solvent containing ions. However, when a pair of biomolecules are in close proximity — about to form a complex or reject forming a complex — the molecular surfaces can be approximated as planar. Therefore a system of two charged semi-infinite half spaces separated by a layer of solvent containing ions is here examined at the Debye-Hückel level with the same mathematical rigor as was developed previously for spheres. Interesting and counterintuitive behavior is found when the charges are of very different magnitude. |
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N00.00333: Biomechanical activation and subcellular force adaptation in the peripheral mechanosensory system Stephen L Holtz, Rachel I Wilson The senses of hearing and touch first rely on forces activating specialized primary mechanosensors, then on neurons transmitting encodings of these forces to the brain. We would like to understand how environmental forces impinge on mechanically sensitive structures, and how these forces act within cells to drive neural responses. However, delivering precise mechanical stimulation while recording responses has proven difficult due to mechanosensor inaccessibility. |
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N00.00334: A simulated body approach to understanding motor control in a highly deformable biological body jean-baptiste masson, alexandre blanc, chloe barre, françois Laurent, christian L vestergaard
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N00.00335: Analysis of Multiscale Nuclear Dynamics during Lymphocyte Activation Matthew Connell, Frank Fazekas, Arpita Upadhyaya, Ivan Rey Suarez T cells play an essential role in the adaptive immune response. Through direct interactions via the T cell receptor (TCR), T cells recognize and bind foreign antigens on the surface of antigen presenting cells (APCs), resulting in activation. Following TCR binding and activation, the T cell spreads onto the APC and forms an immune synapse, which is accompanied by changes in cytoskeletal architecture and dynamics as well as nuclear deformation and reorganization. How the mechanical properties of the nucleus, which are governed in part by their chromatin distribution, influence the formation of the immune synapse and thus regulate immune function remains unknown. In this work, we perform high-resolution live cell imaging of T cell nuclei during activation. We tracked individual chromatin loci and overall chromatin flows to characterize dynamics in response to activation and altered chromatin compaction. Our analysis of nuclear dynamics at multiple time and length scales allows us to characterize the restructuring of chromatin architecture and mechanical changes across the nucleus. We find that both T cell activation and modulation of chromatin compaction affect nuclear dynamics on multiple scales, raising important questions about how chromatin dynamics may influence gene expression during early phases of the T cell immune response. |
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N00.00336: Centrosomal Association with Nuclear Invaginations: Implications for T Cell Activation Frank Fazekas, Ivan Rey-Suarez, Aashli Pathni, Matthew Connell, Arpita Upadhyaya T cells, a key component of the adaptive immune system, are activated when receptors on their surface recognize and bind to pathogenic peptides on antigen-presenting cells (APCs). T cell activation is a dynamic process resulting in dramatic changes to cellular morphology. The centrosome (the microtubule organizing center) migrates towards the immune synapse, the contact region between the T cell and the APC, upon activation. There, the centrosome plays a critical role in establishing cell polarity and directing intracellular transport mechanisms. We have observed that the centrosome maintains a close association with the nucleus throughout the activation process. Using confocal microscopy to study T cells activated on a planar glass surface, we have developed an analysis platform to generate 3D reconstructions of nuclei and characterize the geometry of the nuclear surface. We find that, as the nucleus spreads out and the centrosome migrates towards the synapse upon activation, the centrosome is consistently situated close to a deep invagination of the nucleus. Furthermore, we provide evidence that nuclear invaginations in activated T cells tend to be associated with less condensed chromatin, suggesting that the formation of invaginations may have implications for gene expression. |
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N00.00337: Characterizing the role of vimentin intermediate filament networks in mediating cytoskeletal cross-talk during T cell activation Mikayla Greiner, Aashli Pathni, Frank Fazekas, Matthew Connell, Kiet Nguyen, Ivan Rey-Suarez, Erica Herrera Huaman, Arpita Upadhyaya T cells play a key role in adaptive immunity, initiating a tailored immune response to specific pathogens. Upon activation, T cells undergo dramatic cytoskeletal rearrangements that drive polarization, force generation at the cell-substrate interface (immune synapse), and activation of signaling pathways that promote immune function. While functions of the actin and microtubule (MT) cytoskeletons during activation have been well-studied, the role of intermediate filaments (IFs) is less understood. We examined the role of vimentin IFs in mediating cytoskeletal crosstalk during T cell activation. Using confocal microscopy, we observed that vimentin contracts at the immune synapse upon activation, and that this contraction is regulated by dynein activity and coordinated with centrosome polarization. We additionally used TIRF microscopy to study MT dynamics in activated control and vimentin knock-down Jurkat T cells, revealing higher MT growth speeds in vimentin-depleted cells. Since dynamic MTs have been shown to regulate traction forces during activation, we then used TFM to compare force generation by control and vimentin knock-down cells. Finally, using polyacrylamide gels of tunable stiffness, we examined whether vimentin is required for centrosome polarization and synaptic actin accumulation in response to stiffness. Our results suggest that vimentin mediates cytoskeletal crosstalk during T cell activation, raising questions about the underlying molecular mechanisms. |
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N00.00338: Mechano-metabolism of adherent cells in 2D and 3D microenvironments Joshua M Toth, Anuja Jaganathan, Xingyu Chen, Vivek B Shenoy Cells regulate their metabolic activity in response to the mechanical and chemical properties of their microenvironment. To elucidate how a cell’s morphology, contractility and its energetic demands are controlled by the microenvironment, we developed a non-equilibrium, active chemo-mechanical model that makes quantitative predictions of ATP consumption associated with stress fiber assembly as a function of extracellular matrix mechanical properties. We study the metabolic budget of MDA-MB-231 breast cancer cells cultured in different density 3D collagen gels and on different stiffness 2D polyacrylamide substrates and predict unique trends in cell shape consistent with experimental observations. We show that the cell contractility monotonically increases with stiffness as does the steady state level of ATP consumption. By accounting for the mechano-sensitive activation of AMPK, we show that our model could also predict ATP replenishment, and we find with experimental measurements increasing levels of activated AMPK as a function of matrix stiffness. The insights gained from the predictive model on how the cell tailors its metabolic budget in response to the microenvironment can be used to understand mechanosensitive regulation of metabolic processes and of physiological events such as metastasis and tumor progression during which cells experience dynamic changes in their microenvironment and metabolic state. |
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N00.00339: Mechanical regulation of cytoskeletal dynamics and signaling in cytotoxic T lymphocytes Vishavdeep Vashisht, Aashli Pathni, Lei Li, Neha Narayan, Zhengguo Xiao, Arpita Upadhyaya Cytotoxic T lymphocytes (CTLs) play an integral role in the adaptive immune response. Following engagement of the T cell receptor (TCR) with cognate peptide-MHC on the target cell surface, CTLs release lytic granules containing perforin and granzymes at the CTL-target point of contact, the immune synapse (IS). The cytoskeleton undergoes dramatic reorganization to facilitate synapse formation, targeted granule delivery and force exertion, thus triggering target cell death. CTLs encounter target cells with a range of stiffnesses, from hundreds of pascals to several kilopascals. Prior work has shown that T cell activation, signaling and proliferation depend on substrate stiffness, but the underlying mechanisms remain unknown. We hypothesized that the cytoskeleton plays a central role in mediating this mechanoresponse. We examined the interaction of CTLs with antibody coated elastic hydrogels of tunable rigidity, and found that IS formation, actin accumulation and myosin light chain phosphorylation at the IS are stiffness-dependent. We also found that TCR signaling, centrosome polarization and lytic granule release are tuned by substrate stiffness. These results indicate that synapse formation, early activation and function in CTLs depend on substrate stiffness and suggest that mechanical regulation of the cytoskeleton may be a key factor in modulating this differential response. |
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N00.00340: Branch Points Detection in Automated Reconstruction of Morphological Neural Circuits Via Supervised Machine Learning Hang Deng Automated reconstruction of morphological neural circuits plays a vital role in advancing our understanding of brain function and development, facilitating the discovery of treatments for neurological disorders, and driving progress in artificial intelligence. Manual tracing, due to its labor-intensive and time-consuming nature, is not a scalable solution. However, automated tracing encounters a significant challenge when two axons intersect and merge, leading to substantial errors, particularly in low-resolution microscopy images. |
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N00.00341: To be or not to be: Uncovering the Interplay between Phenotypic Robustness and Plasticity in Gene Regulatory Networks. Anantha Samrajya Shri Kishore Hari, Mohit Kumar Jolly
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N00.00342: The effects of mitochondrial physical properties on insulin secretion in mouse pancreatic beta cell (β-cell) line MIN6 Luis Perez March Meeting 2024 Abstract |
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N00.00343: Exploring the Effects of Implicit Solvent Models and Parameter Variations in Molecular Dynamics via Hybrid Monte Carlo Noah Pishaki, Tyler Luchko The 3D reference interaction site model (3D-RISM) is an implicit solvent model that estimates solvation density distributions and thermodynamics in close agreement with results obtained from explicit solvent models. However, the computational demands of 3D-RISM make its use in molecular dynamics (MD) simulations, where solvation forces need to be updated at every time step, impractical. To overcome this challenge, we adopted the hybrid Monte Carlo (HMC) method to couple 3D-RISM with the fast generalized Born (GB) implicit solvent method. In our implementation, HMC generates global trial moves through MD simulations with GB, which are accepted or rejected using the Metropolis criteria for the Hamiltonian with 3D-RISM. To implement HMC, we developed a Python script that utilizes the Amber molecular modeling suite for executing MD simulations and conducting energy evaluations. To assess the effect of different GB implementations, we conducted HMC simulations of two distinct GB models (GBOBC, and GBn) with 10,000 Monte Carlo steps of 10 ns MD runs. Kolmogorov–Smirnov tests of the resulting Ramachandran plots yields P-values of >0.94, confirming that the distributions are from the same potential, showing that we are sampling from the 3D-RISM Hamiltonian, independent of the GB model. The various GB models for MD in the HMC approach had acceptance rates of 0.45-0.61, giving an effective sampling of up to 600 ns for the longest MD trajectory length. This improved computational sampling denotes a three order of magnitude speed increase for sampling over 3D-RISM with standard MD. Notably, no decrease in acceptance rates was observed when using longer MD runs, suggesting larger speedups in 3D-RISM sampling are possible. |
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N00.00344: Cryo-EM sample preparation using microfluidic cryofixation and cryo-FIB for time-resolved studies MEKIDELAWIT GIRMA TIRFE, Wonhee Lee Understanding the functions of biomolecules requires dynamic studies of their molecular structures. These critical conformational changes occur in a short time scale which makes it challenging to directly study the dynamics using conventional cryo-EM sample preparation, such as blotting. To overcome this limit, time-resolved cryo-EM techniques are developed, which utilize spray deposition of small droplets. The reactions can be initiated in a microfluidic mixing channel or by depositing and mixing two different reactants directly on the grid [1]. Although such techniques allow precise control over the initiation of chemical reactions in the time-resolved cryo-EM, they still suffer from uneven ice thickness and air-water interface issues [2]. We developed a microfluidic cryo-EM sample preparation technique where we freeze the whole microfluidic mixer channel that contains samples with varying reaction times. We fabricated a microfluidics cryofixation system on a cryo-stage with a microheater embedded in a thin parylene film to maintain the liquid sample at room temperature until the sample is ready for vitrification. After we successfully vitrified our sample, we cut out lamellae from the channel at different time points using cryo-FIB. Then the lamellae are transferred into cryoTEM to observe the structural changes that happen over time. This method allows the preparation of time-resolved cryo-EM samples that contain a wide range of reaction times and dynamic changes. We anticipate this system will allow the preparation of diverse types of biological samples for time-resolved cryo-EM studies including dynamics of biochemical reactions and changes in nanostructures of cellular organelles after certain external stimuli are applied. |
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N00.00345: CHEMICAL PHYSICS
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N00.00346: Computational Quantum Quest Towards the Depleted Sulfur in the ISM Namrata Rani, Stefan Vogt-Geisse, Stefano Bovino
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N00.00347: Characterization of photo-enhanced water oxidation in cobalt oxide catalysts using model Co4O4 cubane Zachary J Mast, Michael Mara, Subhajyoti Chaudhuri, Brian Phelan, Elizabeth Ryland, Agnes Thorarinsdottir, Tetsuo Katayama, Daniel Nocera, George C Schatz, Lin X Chen Hydrogen generation through water oxidation would allow for an abundant resource that could replace fossil fuels as a primary source of energy. Water oxidation catalysts still operate at high overpotentials, and the dominant mechanisms for O–O bond formation are still under debate. The cobalt oxide catalyst CoPi is a type of water oxidation catalyst that, in addition to its similarity to the oxygen evolving complex in photosystem-II, has photocurrent effects which have selective enhancement and inhibition of catalytic activity depending on the wavelength of light—600 nm and 400 nm, respectively. Understanding these photocurrent effects provides insight into favorable conditions for water oxidation, which could guide the design of future catalysts. However, due to its amorphous structure, it is difficult to characterize the dynamics of CoPi, and thus molecular models provide better resolution. Using Co4O4(OAc)4(Py)4 (Co4O4) as a model for the CoPi active site, the ultrafast excited state dynamics at the 400 nm excitation were probed using X-ray transient absorption at the cobalt K-edge. In combination with quantum chemical calculations, the results here explore the early-time changes in electronic and molecular structure upon excitation. |
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N00.00348: Unveiling the Mechanism of o-fluorophenol Ultrafast Photodecay Maricris L Mayes, Michael Barquilla Excited states play a central role in essential natural processes. For example, tyrosine, a common natural compound, is shielded from UV damage through ultrafast nonradiative photodecay, driven by phenol’s butterfly mode vibration. Intramolecular H-bonding in phenol derivatives like o-fluorophenol disrupts this decay process. The relaxation mechanism of o-fluorophenol remains incompletely understood, as it exhibits both ultrafast and nanosecond decay rates that may follow distinct pathways. Nonadiabatic dynamics simulations were performed using complete active space self-consistent field theory, and transition probabilities were computed using the Zhu-Nakamura theory. Relaxation from S2 is notably inhibited, contrary to prior phenol photodynamic simulations. Relaxation through H-tunneling from S1 is rare. In contrast to the hypothesis, decay via butterfly vibration does not lead to H-dissociation and follows a distinct conical intersection for a longer time. A fraction of the trajectories undergoing H-dissociation persisted on S1, supporting the nanosecond lifetime. These findings highlight the pivotal role of intramolecular H-bonding in impeding the ultrafast relaxation of phenols. Also, theoretical elucidation clarified ambiguous experimental decay routes, revealing two distinct mechanisms. These insights advance the fundamental understanding of excited-state processes in aromatic compounds. |
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N00.00349: Hydrogen Bonding Induced Nonlinear ν(CD) Infrared Cross Sections Ryan McDonnell, Venkata Swaroopa Datta Devulapalli, Tae Hoon Choi, Laura McDonnell, Isabella Goodenough, Prasenjit Das, Nathaniel L Rosi, Karl Johnson, Eric U Borguet The Beer-Lambert law is commonly used to extrapolate the concentration of analytes confined in porous metal organic frameworks (MOFs). However, analytes which hydrogen bond to MOF moieties can induce nonlinear infrared cross sections, or, deviations from the Beer-Lambert law. Here, we employ a combination of Fourier transform infrared spectroscopy and Density functional theory (DFT) techniques to understand the nonlinear infrared intensity behavior of CD3CN diffused into UiO-67 MOFs. Ultra-High Vacuum (UHV) methods are employed to eliminate atmospheric contaminants. We devise a new method to allow vibrationally active probe molecules to diffuse through the MOF and preferentially adsorb to internal sites. We show that the infrared intensities of all ν(CD) modes decrease following diffusion into UiO-67. In other words, the infrared ν(CD) cross sections of CD3CN adsorbed on the exterior of UiO-67 is significantly larger than that for CD3CN adsorbed on the interior of UiO-67. DFT calculations show that the infrared ν(CD) mode intensities decrease due to a significantly reduced dipole derivative following adsorption to µ3-OH sites. These results have implications on the use of integrated infrared intensity for discerning molecular transport kinetics into and out of MOFs. |
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N00.00350: Effect of intramolecular hydrogen bond strength on the ultrafast ESIPT dynamics Diksha Pandey Excited state intramolecular proton transfer (ESIPT) process is a very fundamental and extensively explored photochemical process.1 It belongs to the class of essential and fastest unimolecular processes in nature and has been studied by several ultrafast technologies.2 This processes is initiated by the transfer of a proton from a donor to an acceptor group, which are in close vicinity within the molecule and is regulated by the interplay of nuclear and electronic dynamics. ESIPT reaction has garnered tremendous attention of theoretical and experimental researchers alike, ever since its first reported occurrence by Weller in 1956,3 owing to its peculiar opto-electronic properties as well as its close resemblance to the proton transfer reactions in the biological systems.4 Despite the considerable volumes of research dedicated, the study of ESIPT process continues to pose significant challenges, chiefly because of the intricate nature of its physical and chemical properties, such as quantum nature, cleavage and formation of hydrogen bond, the change in the properties of excited-state hydrogen bond, nuclear rearrange process etc.5
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N00.00351: A Statmech model of water that treats the solvation interface Lakshmanji Verma, Ken A Dill Molecular simulations of biomolecules rely on either explicit water, which is computationally expensive, or implicit water, which can miss much of the interfacial physics. Here we develop a statistical mechanical model of liquid water and its interface with solutes. It has the advantages of being efficient -- because it is a computation, not a simulation -- and of capturing water's tetrahedral hydrogen bonding and spherical Lennard Jones interactions. It entails two steps. First, in Cage Water, we develop a reference state of pure water over the full liquid range vs (T, p) [Urbic, Dill, JACS, 2018]. Second, in Crust Water [Yadav et al, JPCB, 2022], we introduce a spherical solute molecule and populate the solute's surface (i.e. its crust) with these semi-explicit water molecules that we can compute efficiently. Now we further develop this model, more physically and accurately, by introducing ions and predicting ion solvation faithfully. We hope that further developments bring this approach into the computational modeling of biomolecules. |
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N00.00352: The Harmonic and Gaussian Approximations in the Potential Energy Landscape Formalism for Quantum Liquids Yang Zhou, Yang Zhou, Ali H Eltareb, Gustavo Lopez, Nicolas Giovambattista The potential energy landscape (PEL) formalism has been used in the past to describe the behavior of classical low-temperature liquids and glasses. Here, we extend the PEL formalism to describe the behavior of liquids and glasses that obey quantum mechanics. In particular, we focus on the (i) harmonic and (ii) Gaussian approximations of the PEL, which have been commonly used to describe classical systems, and show how these approximations can be applied to quantum liquids/glasses. Contrary to the case of classical liquids/glasses, the PEL of quantum liquids is temperature-dependent and hence, the main expressions resulting from approximations (i) and (ii) depend on the nature (classical vs. quantum) of the system. The resulting theoretical expressions from the PEL formalism are compared with results from path-integral Monte Carlo (PIMC) simulations of a monatomic model liquid. In the PIMC simulations, every atom of the quantum liquid is represented by a ring-polymer. Our PIMC simulations show that, at the local minima of the PEL (inherent structures), sampled over a wide range of temperatures and volumes, the ring-polymers are collapsed. This facilitates considerably the description of quantum liquids using the PEL formalism. Specifically, the normal modes of the quantum liquid can be calculated analytically if the normal modes of the classical liquid counterpart are known (as obtained, e.g., from classical MC or molecular dynamics simulations of the corresponding atomic liquid). |
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N00.00353: Development of Mediator Assisted N' GNN Optimization (MANGO) Project Matthew D Bruenning, Gaige Riggs, Jonathan Kliewer, Rachel Lee, Ridwan Sakidja In this work, we developed a methodology to mediate a series of Machine Learning Interatomic Potentials (MLIP). In general, active learning protocols for each MLIP still typically relies on a direct sampling to DFT calculations, resulting in an effectively "low bandwidth" learning process due to the inherent limitation in the DFT sampling. We propose to use a mediation process that interactively connects several known MLIP's, culminating in the development of GNN-based models, so that the "ground truth" sampling needs not to solely rely on the extensive ab-initio calculations. Rather, our Mediator Assisted N' GNN Optimization (MANGO) project aims at creating an ecosystem within which the higher fidelity MLIP's (e.g., the ones employing symmetry equivariant features) can be employed to assist the active learning protocol to optimize the lower fidelity MLIP's (e.g. the ones relying on symmetry invariant latent space). This "high bandwidth" learning approach would allow us to use larger sized samples to help evaluate, for example, long-range interactions and to produce more diverse but relatively higher fidelity MLIP models requiring less computational (GPU) resources. The use of open-source DFT codes would also be integrated to widen the development of MLIP's "for the masses." The partial support from the NASA-MOSGC is gratefully acknowledged. |
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N00.00354: Machine Learning/Molecular Mechanics (ML/MM) methods for the simulation of chemical reactions Adrian Gordon, Clara Kirkvold, Jason D Goodpaster, Varun Gopal, Sapna Sarupria Quantum Mechanics/Molecular Mechanics (QM/MM) methods have been instrumental in simulating biological systems such as enzyme catalyzed reactions. However, the efficiency of QM/MM simulations is greatly limited by the cost of the QM calculation. Machine learning potentials offer a solution to this computational bottleneck. Machine learning potentials are capable of predicting energies and forces at the quantum mechanical level of accuracy, but at a fraction of the cost. In this work we combine machine learning with a QM/MM approach to develop a ML/MM method in order to study solvated reactions and enzyme catalysis. |
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N00.00355: Investigating Economic Methods for the Detection of Lead Ions in Drinking Water Lucas LiaBraaten, Lifeng Dong We aim to develop two economic methods to detect lead ions in drinking water. One is to synthesize bismuth nanoparticles to replace gold and silver nanoparticles used in surface-enhanced Raman spectroscopy. The other is the applicability of using 4-aminothiophenol (4-ATP) to directly react with lead ions. For bismuth nanoparticle synthesis, we successfully used lemon juice as both a reduction and capping agent, which helps to serve as a green alternative to traditional nanoparticle synthesis. The diameter of the bismuth nanoparticles were found to be around 50 nm through scanning electron microscopy characterization. As for the 4-ATP method, we found that lead ions and 4-ATP react to form a visible shard-like precipitate as well as a much smaller branch-like precipitate that sticks to microscope substrates. Light microscope images showed differences in the amount and morphology of the precipitates as the concentration of lead was changed from 25 μM to 2.5 μM. These findings will help us to further utilize bismuth nanoparticles for Raman spectroscopy and to understand the reactions between 4-ATP and lead ions for assessing lead ions in water. |
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N00.00356: Determining the out-of-plane sound speed in GeS by time-resolved broadband transient reflectivity Watheq A Al-Basheer, Christian Viernes, Meixin Cheng, Ruofei Zheng, Sam Netzke, Kostyantyn Pichugin, German Sciaini Over the past decade, 2D semiconducting materials, with their distinctive structure and unique physicochemical properties, have drawn attention for potential applications in photonics and optoelectronics. Germanium sulfide (GeS) is a 2D anisotropic semiconductor with a 1.65 eV indirect bandgap. This study will present and explain time-resolved broadband transient reflectivity measurements in a single GeS crystal. Femtosecond (fs) stimulated Brillouin scattering, combined with fs-broadband probe measurements, has been utilized to evaluate the out-of-plane sound speed 3297 ± 100 m/s, in a single GeS crystal. The reported results demonstrate the strength of this non-destructive, all-optical technique for studying elastic properties in frail two-dimensional layer materials, such as semiconductors from the group-14 transition metal monochalcogenides. |
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N00.00357: Resonance Raman Intensity Analysis of Photoactive Metal-Organic Frameworks Joe Brennan, Tae Hoon Choi, Zoe M Soilis, J Karl Johnson, Nathaniel L Rosi, Renee R Frontiera Plant photosystems are highly efficient light-harvesting constructs and their properties have inspired scientists to mimic their design for photochemistry and energy storage. Here we present a biomimetic light harvesting and energy storage system based on scaffolded metal-organic frameworks. To optimize the light-harvesting process it is important to understand the dynamics of the materials when they interact with light, in order to reduce any energy loss pathways. To investigate these dynamics, we have studied four (NH2)2 UiO-68 MOFs with aldehyde modifier groups attached at one of the amino positions, which results in varying photophysical properties such as electronic transition energy (475-535 nm) and fluorescent quantum yield (0.16% - 0.41%). To probe these samples, we use resonance Raman intensity analysis (RRIA), which quantifies how the MOF linkers distort in the excited state and identifies the vibrational pathways responsible for energy dissipation. We found that the C-C stretches of the aromatic rings furthest from the modifier are most distorted upon excitation relative to the other moieties, including those closer to the modifier such as the C-C stretches of the rings attached to the functional group. This reveals that the vibrations of the rings furthest from the functional group are responsible for a disproportionate amount of energy loss relative to the rest of the MOF and in future designs should be constrained to increase energy collection. |
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N00.00358: Rotational Spectroscopy Studies on Hydrogen Bonding Aaron J Reynolds, Kenneth R Leopold, Wei Lin, Karla Salazar Proton transfer across a hydrogen bond represents the simplest of chemical reactions, but one which |
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N00.00359: Experimentally Investigating the Thermodynamic Adsorption Limits of Carbon-Based Electrodes for Capacitive Deionization (CDI) Hunter J Nelson, Grant Cary, Daniel Moreno Capacitive Deionization (CDI) is an electrochemical water purification process through which an electric potential is applied across carbon-based electrodes. The goal for this study is to improve the absorption limits for electrodes and predict maximum performance relative to thermodynamic limits. By calculating the enthalpy and entropy we can understand the energy levels, system capacity, and nature of the adsorption process (physisorption vs. chemisorption). Much of this work can be done computationally but further experimental verification is needed to validate the modeling. Each electrode was tested to obtain the removal of salt at variable concentrations and temperatures using a thermal flow cell, capable of heating to maximum tested temperature of 50°C. The experiments pushed saline solution through the 10x10 cm thermal cell at 5mL/min, where it would be charged and discharged to 1.2V and –1.2V respectively. The results confirmed previous trends where higher concentrations would increase capability for salt removal, but only up to a certain maximum value. Upon testing a range of temperatures and concentrations, enthalpy and entropy adsorption characteristics for the adsorption can be predicted, generally suggesting physisorption (low enthalpy) for low salt removal. Moving forward, the goal is to maintain the experiments and continue with more concentrations of saline solutions and alternative voltage values. |
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N00.00360: Highly Rotationally Excited N2 Reveals Transition-State Character in the Thermal Decomposition of N2O on Pd(110) Barratt Park, Jiamei Quan, Rongrong Yin, Zibo Zhao, Ximei Yang, Alexander Kandratsenka, Daniel J Auerbach, Alec M Wodtke, Hua Guo We employ time-slice and velocity map ion imaging methods to explore the quantum-state resolved dynamics in thermal N2O decomposition on Pd(110). We observe two reaction channels: a thermal channel that is ascribed to N2 products initially trapped at surface defects and a hyperthermal channel involving a direct release of N2 to the gas phase from N2O adsorbed on bridge sites oriented along the [001] azimuth. The hyperthermal N2 is highly rotationally excited up to J = 52 (v″ = 0) with a large average translational energy of 0.62 eV. Between 35 and 79% of the estimated barrier energy (1.5 eV) released upon dissociation of the transition state (TS) is taken up by the desorbed hyperthermal N2. The observed attributes of the hyperthermal channel are interpreted by post-transition-state classical trajectories on a density functional theory-based high-dimensional potential energy surface. The energy disposal pattern is rationalized by the sudden vector projection model, which attributes to unique features of the TS. Applying detailed balance, we predict that in the reverse Eley–Rideal reaction, both N2 translational and rotational excitation promote N2O formation. |
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N00.00361: Oscilatory behaviour observed in the kinetics of reversible proton transfer reactions in aqueous solutions. Ehud Pines, Dina Pines Photoacids undergo ultra-fast reversible proton transfer reactions to and from liquid aqueous and non-aqueous solutions. The oscillation period depends on the excited-state acidity of the photoacid and at least one competing reversible proton acceptor site. This result is proton dissociation profiles still exhibiting at very long times a t-3/2 dependence over time with population oscillations super imposed on it. We have recently observed oscilatory behaviour in the long time tail when there is a two- site competition for the proton when both sites exhibit reversible proton binding following the initial proton dissociation event into the solution. Over even longer times, which depend on the proton retention time at the competing protonation site, the proton is ultimately released into the bulk solution. Our kinetic model captures all details of this complex kinetic system and we carry out full simulations of the coupled diffusion multi-reactive kinetic system which after best-fitting the multi-reaction parameters gives synthetic reaction profiles indistinguishable from the measured ones. |
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N00.00362: Poster: Resonance Theory of Vibrational Polariton Chemistry Wenxiang Ying, Pengfei Huo We perform numerically exact quantum dynamics simulations using the hierarchical equation of motion (HEOM) approach to investigate the resonance modification of chemical reaction rate constants due to the vibrational strong coupling (VSC) in polariton chemistry. The results reveal that the cavity mode acts like a ``rate-promoting vibrational mode" that enhances the ground state chemical reaction rate constant when the cavity mode frequency matches the vibrational transition frequency. The VSC-modified rate constant will first increase quadratically, then quickly saturate and decay as the Rabi splitting $Omega_R$ increases. When changing the cavity lifetime $ au_c$ from the lossy to the lossless limit, the numerical results show there will be a turnover of the rate constant. With given $Omega_R$, the resonance enhancement of VSC rate is proportional to $ au_c$ in the lossy limit of $ au_c ll 1 / Omega_R$, and to $1 / au_c$ in the lossless limit of $ au_c gg 1 / Omega_R$. We further present an analytic rate theory based on Fermi's golden rule to explain the observed behaviors of VSC rates, including the sharp resonance peak and origin of its broadening, the effects of $Omega_R$ and $ au_c$, resonance condition at the normal incidence, etc. To the best of our knowledge, this is the first analytic theory that clearly illustrates the reaction mechanism under VSC modifications, and is able to explain the sharp resonance behavior of the VSC-modified rate profile with quantitative accuracy. |
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N00.00363: Elucidating water's underlying local structures by decomposing the orientational order parameter distribution Bilin Zhuang, Hua Yuan, Akanksha D Chokshi, Diya Sanghi Water is simultaneously the most common liquid on earth and the weirdest, judging from the variety of its anomalous properties. For example, water has a density maximum at 4 degrees Celsius, while other simple liquids just expand on heating. The "weird" nature of water may be explained if it is seen as a mixture of two different local structures. However, the two structures have not been elucidated in scientific literature. In this work, we attempt to discover the distinct underlying structures contributing to water's anomalous behaviors by decomposing the distribution in the orientational order parameter into simple modes involving molecules normally distributed around geometric centers. We find that water can be classified into two groups. In the first group, water molecules have neighbors arranged in an ice-like tetrahedral manner, and in the other group, water molecules have neighbors arranged in a trigonal bipyramidal manner. Our finding confirms the coexistence of different local structures in liquid water and provides a method to access the fraction of the different structures for spectroscopic studies and thermodynamic theories. |
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N00.00364: A Path to Organic Faraday Rotators: Reinvestigation of the Magneto-Optical Properties of Polythiophenes Angelina Rogatch From optical isolation to magnetic field detection and imaging, magneto-optic devices have become an integral part of our lives. While these technologies traditionally rely on expensive, inorganic substances with limited versatility for device architectures, a new generation of organic semiconducting polymers is being evaluated as a promising substitute. The magneto-optic activity of materials is determined by their performance in a phenomenon known as Faraday rotation, where linearly polarized light rotates as it passes through a transparent medium in the presence of an external magnetic field. Polythiophenes, a class of common organic materials, have been reported to exhibit exceptional magneto-optical properties, surpassing the performance of traditional inorganic materials; however, this study shows that the reported results were irreproducible. We propose that the observed discrepancy is linked with the degree of regioregularity of the polymer and offer a mechanistic explanation of the origin of polymer errors, uncovering an important structure-activity trend in organic magneto-optical materials. This work aims to shed light on the general principles for enhancing the magneto-optical performance of organic materials, paving the way for their broader application in novel technologies. |
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N00.00365: Abstract Withdrawn
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N00.00366: Cc4s - a high-performance coupled-cluster simulation code for solids and surfaces Andreas Irmler, Felix Hummel, Alejandro Gallo, Tobias Schaefer, Andreas Grueneis We present the open-source ab initio simulation software Cc4s. The target applications of Cc4s are highly accurate electronic structure theory calculations of solids and surfaces using the quantum chemical coupled-cluster ansatz. The high computational cost of the CCSD(T) calculations can be overcome using the state-of-the-art high-performance tensor library CTF, allowing for efficient calculations on tens to hundreds of compute nodes. Our code interfaces with the VASP package for the calculations of the Hartree-Fock reference and related quantities. |
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N00.00367: Simulations of Photochemistry Inside An Optical Resonator Landon Johnson, Dmitri Kilin Photochemistry has opened the door to new materials and new fabrication processes. However, accurate descriptions of their underlying photophysical properties and mechanisms are necessary to systematically improve designs and fabrication processes. Providing such descriptions remains an open challange. These photophysical properties and mechanisms inherently arise from the simultaneous coupling of quantized nuclear, electronic, and photonic degrees of freedom (DoF), for which there are no analytical solutions except in the simplest of cases. |
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N00.00368: Robust strategies for non-orthogonal multi-configuration self-consistent field wavefunctions : Hessian optimization techniques Zihui Song The recently developed orbital optimized non-orthogonal multi-configurational self-consistent field (NOMCSCF) approach is one of several different-orbitals-for-different-configurations (DODC) methods. This method allowed the optimization to start from an arbitrary initial states, and finds the best set of orbitals in a DODC framework. Additionally, DODC methods provide an intuitive connection to the diabatic picture that is required for describing nonadiabatic processes such as energy and electron transfer. A nonorthogonal quasi-diabatic basis has advantages compared to using an orthogonal determinant basis because the need for diabatization can be avoided, and the wavefunction is computed directly in a simple and chemically intuitive framework. To improve applicability of the NOMCSCF model, robust and efficient of optimization strategies for NOMCSCF type wavefunctions is necessary. In this work, I present the development of the NOMCSCF analytical Hessian, which accounts for different orthogonality regimes of the generalized Slater Condon rules. I illustrate how the NOMCSCF analytical Hessian can be used for analysis of NOMCSCF wavefunction stability,as well as in developing robust optimization strategies. |
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N00.00369: Untangling perturbations to lipid membrane hydration induced by polystyrene nanoplastics through multiscale simulation and experiment Zeke A Piskulich, Laura Kesner, Zeev Rosenzweig, Qiang Cui Understanding the impact of anthropogenic nanoparticles on the phase behavior, dynamics, and stability of biological membranes has been a longstanding area of interest within chemical and biological physics. In particular, it has been of recent interest to understand how nano-sized plastic particles (nanoplastics), which originate from the breakdown of microplastics, drive changes in the membrane structure and dynamics. Using uncrosslinked polystyrene nanoparticles as a model for nanoplastic particles, Laurdan fluorescence spectroscopy experiments have observed a concentration dependent blue shift that would typically be interpreted as a fluid to gel membrane phase transition for traditional nano-bio interactions. In the present work, we demonstrate using multi-scale molecular dynamics simulations that this does not appear to be the case; it instead appears that the flexible, hydrophobic nature, of polystyrene nanoparticles allows them to penetrate and dissolve into the membrane interior leading to a dehydration of Laurdan probe molecules that confounds traditional interpretation of Laurdan fluorescence. Specifically, using coarse-grained molecular dynamics simulations we demonstrate that polystyrene nanoplastic particles are able to rapidly penetrate into lipid membranes and dissolve into the hydrophobic interior of the membrane. Then, using all-atom molecular dynamics simulations, we show that this process results in a dehydration of both the membrane and the Laurdan fluorescent probe. Lastly, using QM/MM calculations we demonstrate that this dehydration, rather than membrane phase change, induces a spectroscopic blue shift of Laurdan probe molecules incorporated within the membrane. These results will then be discussed in the context of nano-bio interactions, and their implications for understanding the biological impact of these nanoparticles. |
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N00.00370: Essential Amino Acids - Detection on a GaAs Chip and via Machine Learning William L Rye, Tamador Alkhidir, Deborah L Gater, Abdel F. Isakovic We demonsrate that it is possible to detect all essential amino acids in a water solution on a GaAs chip, at ambient conditions. The chip is made of AlGaAs/GaAs heterostructure in a simple microfluidfic configuration, and the detection method is based on differential conductance. We identify between 3 and 7 characteristic peaks for each amino acid that can be used for idenitification putposes in machine learning algorithms. Our experiments show the changes in Debye length as we alter the pH factor of the solution, pointing towards optimum detectability for various amino acids. In parallel, we find correlations between the X-ray absorptivity of amino acids, their detectability on our chips and some of their physico-chemical properties. |
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N00.00371: Estimating Thermally Driven Magnetic Field Fluctuations near Nanoscale Ferromagnets - Understanding Signal Loss in Magnetic Resonance Force Microscopy (MRFM) Russell W Burgett, John A Marohn, Robert D McMichael Many spin-based quantum computing proposals involve carrying out electron or proton (spin) magnetic resonance very close to a magnet [1]. Additionally, nitrogen-vacancy center imaging and magnetic resonance force microscopy (MRFM) employ nanoscale magnets close to spins [2,3]. One potential problem in these experiments is loss of signal due to unwanted spin-lattice relaxation caused by stochastic magnetic field fluctuations [4]. We present a novel simulation protocol - ground, excite, ring, Fourier transform (GERFT) - to estimate thermomagnetic fluctuations in nanoscale ferromagnets. Using NIST's Object Oriented Micromagnetic Framework (OOMMF) code, we apply a pulsed magnetic field at a point of interest, calculate the resulting transient change in magnetization at each location in the ferromagnet, and use a Fourier transform fluctuation-dissipation theorem relation to compute the power spectral density of field fluctuations at the point of interest. GERFT estimates spin-lattice relaxation times due to fluctuations from common ferromagnetic materials to be 6-7 orders of magnitude longer than would cause significant signal loss in MRFM experiments. The insights provided by this model will lead to higher resolution spin imaging experiments and better designed quantum spintronic devices. |
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N00.00372: Energy transfer interactions between a terbium(III) complex and plasmonic metal nanoparticles Lauralee E Hurst, Justin Stace, Davon W Ferrara Metal nanoparticles (NPs) exhibit interesting opto-electronic properties such as a surface plasmon resonance, which results from collective oscillations of free electrons upon excitation by specific frequencies of incident light. Interactions between this plasmon resonance and other molecules can result in complex energy transfers within the NP system. Resonant energy transfers of lanthanide ion such as terbium(III), which glows yellow-green under short-wave radiation, have been studied extensively; however, there is a unique opportunity to explore plasmonic NP's influence in the resonant energy transfers which can quench or enhance the ion's luminescence. A one-pot synthesis of a novel terbium(III) compound coordinated 4-mercaptobenzoic acid, a bifunctional ligand, is reported, and a protocol to coordinate metal NPs to the available thiol group of the terbium(III) complex ligand is proposed. Optical spectroscopy was used to monitor the absorption and emission of the NP system and used to propose mechanisms of energy transfer of the system. NMR and FTIR spectra were used to characterize the physical properties of the system. Future applications for this system include adaption as luminescent probes. |
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N00.00373: Impact of covalent functionalization of carbon nanotubes on their optical properties: Computational insights Svetlana Kilina Our simulations of covalently functionalized CNTs have complimented and advanced recent experimental efforts in spectroscopy and chemistry of CNTs. A covalent binding of molecular adduct to the CNT, introducing sp3-hybridized defects into the sp2-lattice of the nanotube, results in redshifted optically active transitions providing defect-originated emission at the near infrared (NIR) range. Also, the sp3-defect in CNTs creates a required condition for single photon emission tunable from NIR to telecom wavelengths and achievable at room temperature. We have compared calculated and experimental results from pump-dependent low-temperature photoluminescence spectroscopy and identified the role of tube’s chirality, tube’s mode, adduct polarity, and defect-defect interactions in selective control of defect-associated emission of CNTs. Our results demonstrate that manipulation of the tube chirality together with the polarity and bond character of molecular adducts is a practical strategy for precise tuning of light emission in functionalized CNTs. Overall, our research outcomes have established foundation for the novel material design for solar energy conversion, sensing, and quantum technologies.
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N00.00374: Heterogeneous nucleation of urea from aqueous solutions: a combined experimental and simulation approach Karen Johnston, Samira Anker, Paul Mulheran, Jan Sefcik, David McKechnie Crystallisation is an essential separation process with many applications across the food, chemical and pharmaceutical industries. Current understanding of crystal nucleation mechanisms is limited, which makes controlling nucleation rate and polymorphism a major challenge for developing better crystallisation processes. Primary nucleation is likely to be heterogeneous, and occur at solution-container or solution-impurity interfaces. Previous work on glycine aqueous solutions found that PTFE and tridecane interfaces significantly increased nucleation rates1,2, which was attributed to an interfacial concentration enhancement, which was observed in molecular dynamics (MD) simulations1,3. |
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N00.00375: Swelling thermochemistry and temperature-dependent adsorption of swellable organically modified silica Hannah Savoy, Garrett Worden, Nicholas Gaba, Susan Y Lehman, Paul Bonvallet Swellable organically modified silica (SOMS) is a crosslinked polysilsesquioxane network that swells upon contact with organic solvents. Basic performance parameters such as the volume of swelling and total adsorption capacity are identical among a range of solvents at room temperature. Constant-pressure calorimetry demonstrates that the enthalpy of swelling varies, both in magnitude and mathematical sign, with the identity of the organic solvent. No clear trend exists between the enthalpy of swelling and the polarity or viscosity of the solvent causing the swelling. A series of variable-temperature experiments establish a slight temperature dependence of the enthalpy of swelling, with higher initial temperatures causing the acetone-induced enthalpy of swelling to decrease in magnitude (become less exothermic). The solvent adsorption capacity of SOMS also changes with temperature, albeit in different ways. At higher initial temperatures the adsorption capacity of the material sold under the trade name Osorb decreases, but increases for the less-crosslinked material known as Cyclasorb. Our calorimetry experiments build a foundation from which to characterize the thermodynamics of swelling SOMS for applications in actuators and sensors. |
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N00.00376: Exploring Exciton Transport Dynamics Using Spatially Offset Femtosecond Stimulated Raman Spectroscopy Pauline Lynch, Renee R Frontiera Understanding exciton transport in photovoltaic materials is vital for exploiting their full potential, but there is a lack of research into how molecular structure can be manipulated to tune ultrafast dynamics. Recently, our lab developed spatially offset femtosecond stimulated Raman spectroscopy (SOFSRS) to fill this void. This novel advanced microscopy technique combines the high structural specificity of traditional FSRS with the ability to observe ultrafast dynamics on time and length scales relevant for charge transport behavior. Here, I will discuss recent improvements to this technique to study the role of lattice phonons in exciton transport in crystalline organic materials. Results indicate transport occurs preferentially along the long axis in a pentacene crystal. These results are a promising indication of how SOFSRS can be used to understand transport dynamics in a variety of systems. |
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N00.00377: Understanding the spatial distribution of SERS enhancement across AuFON substrates to control reactivity MaKenna M Koble, Renee R Frontiera Densely packed nanoparticles, such as gold film over nanosphere (AuFON) substrates, have multimodal plasmonic resonances that arise from short- and long-range coupling between nanostructures. When excited, the plasmonic resonance generates an intense, localized electromagnetic field that is useful in a variety of applications, including optical waveguides, nanophotonics, biological sensing, and driving chemical reactions. Our work investigates the relationship between the EM field generated from different plasmonic resonances and the substrate’s geometry. Understanding this relationship can be used to control the spatial extent of reactivity by selectively exciting specific regions on the substrate. I used confocal Raman microscopy to excite specific plasmon resonances with different wavelengths and then mapped the SERS intensity of an absorbed molecule across the substrate. The Raman microscopy images showed that the spatial distribution of SERS intensity across the AuFON varies with laser wavelength. This result indicates that different wavelengths of light can enhance specific regions on the plasmonic substrate and could be used to spatially control chemical reactions. My experimental work has been supplemented with 3D simulations in COMSOL to produce a theoretical localized surface plasmon resonance and investigate the electromagnetic field distribution around the AuFON substrate. The simulations show that certain wavelengths produce EM fields at the tops of the nanostructure while other wavelengths have localized EM fields between the crevices. My work aids in uncovering the connection between substrate geometry and plasmonic response, which helps advance the logical design of plasmonic substrates. |
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N00.00378: Speaker Moved
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N00.00379: Correlated noise can enhance fidelity in entangled quantum qubits. Eric R Bittner It is generally assumed that environmental noise from thermal fluctuations is detrimental to preserving coherence and entanglement in a quantum system. In the simplest sense, dephasing and decoherence are tied to energy fluctuations driven by coupling between the system and the normal modes of the bath. Here, we explore the role of noise correlation in an open-loop model quantum communication system whereby the ``sender'' and the ``receiver'' are subject to local environments with various degrees of correlation or anticorrelation. We introduce correlation within the spectral density by solving multidimensional stochastic differential equations and introduce these into the Redfield equations of motion for the system density matrix. We find that correlation can enhance the fidelity and purity of a maximally entangled (Bell) state. Moreover, by comparing the evolution of different initial Bell states, we show that one can effectively probe the correlation between two local environments. These observations may be useful in the design of high-fidelity quantum gates and communication protocols. |
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N00.00380: Double Quantum Two-Dimensional Electronic-Vibrational Spectroscopy - A Vibronic Perspective of Conical Intersections. Gerrit N Christenson, James D Gaynor Nonadiabatic phenomena are ubiquitous in polyatomic molecular systems and are responsible for many ultrafast dynamics that are not well defined within the Born-Oppenheimer approximation. Conical intersections offer ultrafast, sub-100 femtosecond pathways for efficient electronic relaxation between potential energy surfaces, where the electronic and vibrational degrees of freedom become strongly coupled. The temporal and spectral resolution required to detect conical intersections has made their experimental observation considerably challenging. We propose using double quantum coherence two-dimensional electronic-vibrational (2Q 2D EV) spectroscopy as an experimental approach to monitor vibronic dynamics around a conical intersection, using a mixture of broadband visible and infrared pulses. Here, we develop a semi-classical 3-level system model Hamiltonian that characterizes the coupling between high- and low-frequency vibrational modes that are involved in the conical intersection formation. This Hamiltonian is used to simulate 2Q 2D EV spectra of a photoexcited system passing through a conical intersection. We demonstrate 2Q 2D EV spectroscopy as a helpful tool in identifying nonadiabatic phenomena using vibronic coherences. |
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N00.00381: Towards Probing High Order Anharmonicities of a Strong Oscillator Kelson Oram, Kent A Meyer, John C Wright Overtones and combination bands relate directly to the potential energy surface and grant insight into the couplings present within a molecule. Rhodium dicarbonyl (RDC) is a model compound for nonlinear spectroscopy due to the high oscillator strength of its carbonyl modes. Previous works have studied the anharmonicities of RDC, yet recent developments enable studies of higher order vibrational anharmonicities. We use a novel femtosecond laser system to perform coherent multidimensional spectroscopy, probing high order overtone and combination bands of the carbonyl stretches. This experiment determines the amount of anharmonicity present and maps out the potential energy surface of the molecule. Two independent infrared frequency beams scan across the resonances of the carbonyl stretches and their overtones and combination bands, forming multiple quantum coherences of the vibrational states. A visible excitation upconverts the coherent output, enabling better detection and isolation of the coherent, phase-matched output beam. Our laser system delivers pulses intense enough and broad enough in bandwidth for multiple interactions to occur for each pulse. The multiple laser interactions will coherently climb the vibrational ladder of the molecule to probe the higher order anharmonicities. The results of this experiment demonstrate the extent of the anharmonic oscillator that may be probed using coherent multidimensional spectroscopic techniques. |
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N00.00382: Preparing Hartree-Fock Ansatze with a Polylogarithmic Two-Qubit Gate Depth Circuit on a Quantum Computer Chong Hian Chee, Daniel Leykam, Adrian Mak, Dimitris G Angelakis
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N00.00383: Enhancement of Polariton Coherence Due to Collective Coupling Effect Xiong Kai Benjamin Chng, Wenxiang Ying, Yifan Lai, Nick Vamivakas, Steven T Cundiff, Todd D Krauss, Pengfei Huo Molecular polaritons, which are hybridization of matter states from molecules with photons in a cavity, play an important role in fundamental quantum science and technology. However, molecular polaritons experience significant decoherence due to interactions between the molecules' matter states and their corresponding vibrational states. In this work, we show that, despite such decoherences, hybridizing many molecules in a cavity provides enhancement to the overall quantum coherence of the hybrid states due to collective light-matter coupling effect. Numerical results from the hierarchical equations of motion dynamical method provide validation of this collective coupling effect on the coherence lifetimes. |
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N00.00384: Computational Screening and Designing Solid Sorbent Materials for CO2 Capture Yuhua Duan Combustion of fossil fuels has brought a drastic increase of CO2 concentration in the air causing global warming. To fight climate change, CO2 emissions must be mitigated through capture and storage. Solid sorbents are promising candidates for CO2 sorbents due to their high CO2 absorption capacities at moderate working temperatures. By combining database mining with ab initio thermodynamic calculations, we have proposed and validated a theoretical screening methodology to identify the most promising CO2 sorbent candidates from a vast array of possible solid materials. The advantage of this method is that it identifies the thermodynamic properties of the CO2 capture reaction as a function of temperature and gas pressure without any experimental input beyond crystallographic structural information of the solid phases involved. The calculated thermodynamic properties of solid materials versus temperature and pressure changes were further used to evaluate the equilibrium properties for CO2 adsorption/desorption cycles. The selected candidates were further considered for experimental validations. In this presentation, we elucidate the screening results from the given database and demonstrate a way to design new sorbents for different CO2 capture technologies by mixing different solids. |
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N00.00385: Remediation of Per- and Polyfluoroalkyl Substances in Landfill Leachate using PW12-TiO2 Photocatalyst Brennan Halsey, Addam Ben-Abdallah, Daniil Ivannikov, Sebastian Sage, SESHA S SRINIVASAN, Scott Wallen Per- and polyfluoroalkyl substances (PFAS) represent a class of highly durable chemical compounds extensively employed in various industries, owing to the remarkable stability conferred by the carbon-fluorine bond. These compounds, along with their persistent breakdown products, exhibit detrimental environmental impacts with levels exceeding EPA health advisory limits (concentrations at the parts per trillion, ppt) in many publicly owned treatment works (POTW) and high levels of contamination throughout a broad distribution of water bodies and other ecosystems globally. Compounding environmental concerns, studies have established a correlation between certain PFAS compounds and detrimental health effects in both humans and animals, including but not limited to cancer and birth defects. |
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