Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session M33: Microscopic Self-Assembly I |
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Sponsoring Units: DSOFT Chair: Stuart Thomson, University of Bristol Room: Room 225 |
Wednesday, March 8, 2023 8:00AM - 8:12AM |
M33.00001: Microbial interaction with micrometer-scale wrinkled surfaces subjected to fluid shear Luca Pellegrino, Giovanni Savorana, Cristina Belgiovine, Valeriano Vinci, Benedetta Agnelli, Gerardus Janszen, Luca Di Landro, Marco Klinger, Eleonora Secchi, Joao T Cabral, Roberto Rusconi Surface properties influence bacterial adhesion, which is the first step towards colonization and biofilm formation. For implantable devices, such as catheters, biofilm-associated infections are the most common clinical complications, given their resistance against mechanical stress and antibiotics; therefore, it becomes of paramount importance the design and fabrication of surfaces able to prevent or reduce bacterial colonization. We investigated the effect of micrometer-scale surface wrinkled topographies subjected to fluid shear on the attachment and proliferation of different bacterial species and strains characterized by defined shape (spheroidal Staphylococcus aureus and Enterococcus faecalis, rod-like Pseudomonas aeruginosa and Escherichia coli) and motility (motile, non-motile). Specifically, sinusoidal (1D), checkerboard (C), and herringbone (H) patterns were fabricated by mechanical wrinkling of plasma-oxidized polydimethylsiloxane (PDMS) bilayers and contrasted with flat (F) surfaces. In static conditions, microbial deformation and orientation were found to correlate with the aspect ratio and commensurably with surface pattern dimensions and local pattern order, ultimately describing a linear scaling between bacterial areal coverage and available surface area. Furthermore, to evaluate the effect of topography over bacterial attachment in dynamic conditions, 1D wrinkled topographies were incorporated into microfluidic channels oriented according and in opposition to the flow direction. Significantly, the combination of topography and flow is found to disrupt the spatial arrangement of bacteria, impeding proliferation for several hours and reducing it (by up to ~50%) thereafter compared to flat (F) surfaces. Our findings suggest an effective framework to rationalize the impact of micrometer-scale topography, in static and dynamic conditions, and demonstrating that the judicious combination of surface patterning and fluid shear provides an effective strategy to delay and frustrate the early stages of bacterial proliferation. |
Wednesday, March 8, 2023 8:12AM - 8:24AM |
M33.00002: Nanoscale porosity in microellipsoids controls interparticle capillary attraction and assembly at fluid interfaces Peter J Beltramo, Samuel Trevenen, Heather Hamilton, Anisur Rahman, Alexander E Ribbe, Laura C Bradley Anisotropic particles pinned at fluid interfaces tend towards disordered multi-particle configurations due to large, orientationally-dependent, capillary forces, which is a significant barrier to exploiting these particles to create novel functional self-assembled materials. To create long-range ordered structures with complex configurations via interfacially trapped anisotropic particles, control over the interparticle interaction energy is necessary. In this presentation, we discuss the synthesis of colloidal ellipsoids with controlled nanoscale surface topography (roughness and porosity) and show how this surface topography attenuates the interparticle capillary attraction at a water-air interface. We show that porous particles exhibit a much shorter-range capillary interaction potential, with scaling intriguingly different than theory describing the behavior of smooth ellipsoids. Interferometry measurements of the fluid deformation surrounding a single particle shows that the interface around porous ellipsoids does not possess the characteristic quadrupolar symmetry of smooth ellipsoids, and quantitatively confirms the decrease in capillary interaction energy. Lastly, we show how this reduction in interparticle capillary attraction and alteration in interfacial pinning manifests in the overall 2D interfacial assembly of such particles. |
Wednesday, March 8, 2023 8:24AM - 8:36AM Author not Attending |
M33.00003: 3D Printing of Programmable Self-assembly to Bouligand Nanostructures MONIROSADAT(Sanaz) SADATI, Mohsen Esmaeili, Kyle George, Sepideh Norouzi, Jeremy Money, Nader Taheri-Qazvini The emergence of three-dimensional (3D) printing has advanced the fabrication of on-demand architectures for various applications, from functional devices to organs. However, 3D printing is limited to feature size and lacks the nanoscale design of the constituents vital for functional devices. Herein, we combine the "bottom-up" approach with a "top-down" fabrication strategy to program the nanoscale chiral self-assembly of cellulose-based materials in the printed objects. The chiral or helical arrangement, in which layers of nanoparticles/fibers are slightly twisted by a fixed angle relative to the neighboring layers, is known as the origin of the superior fracture resistance of the mineralized chitin in the "smasher-type" mantis shrimp's dactyl club and the vivid metallic colors in beetles. We design our chiral inks based on cellulose nanocrystals to imprint nano- and microscales chiral self-assembly with controlled helical pitch length. The flow-induced alignment intrinsic to the printing process is exploited to direct hierarchical chiral self-assembly in the printed constructs. By tuning the ink formulation, its rheological properties, and printing parameters, we have been able to print architectures with the organized built-in chiral nanostructure. Our biomimetic concept will open the path to developing materials with new optical (dynamic color and photonic properties) and mechanical (toughness, strength) properties, naturally emerging from their nanostructure and transferred into the larger scale printed architectures, expanding 3D printing material technologies well beyond what has been conceived and attempted so far, into a new generation of composite and metamaterials and process design. |
Wednesday, March 8, 2023 8:36AM - 8:48AM |
M33.00004: Liquid Crystalline Coacervates Composed of Chromonic Mesogens and Polyelectrolytes Elizabeth Adeogun, Prateek Verma, Divya Iyer, Samanvaya Srivastava, Karthik Nayani We report on formation of liquid crystalline (LC) coacervates composed of negatively charged polyaromatic molecules and positively charged homopolyelectrolytes. These polyaromatic molecules (such as disodium cromoglycate; DSCG) can self-assemble in aqueous solutions to form rod-like mesogens via π-π interactions. At sufficiently high concentrations (300 mM), these mesogens exhibit long-range orientational order and give rise to LC mesophases. At concentrations (~ 5 mM) that are several orders of magnitude lower than the corresponding bulk LC phase, no mesophases are observed. Surprisingly, addition of polycations to 5 mM DSCG solutions leads to the formation of LC-coacervates that appear as droplets in solution. The local DSCG concentration in these droplets are significantly higher than their surroundings, leading to characteristic bipolar configuration when observed via polarized optical microscopy. We elucidate the charge-driven formation of LC-coacervates by characterizing trends in their compositions, optical textures and rheology via systematic variations of total charge, ionic strength, and temperature of the solutions. |
Wednesday, March 8, 2023 8:48AM - 9:00AM |
M33.00005: Thermodynamics of volume-spanning self-assembly in the squid eye lens Irem Altan, Alison M Sweeney, Viola Bauernfeind Squids have developed spherical eye lenses with a graded refractive index (GRIN) for underwater vision. While the sphericity increases the lens sensitivity, GRIN corrects for spherical aberration. This system is an example of a complex, macroscopic optical device that reaches its optical properties through volume-spanning, error-minimizing self-assembly, a feat that is currently unreachable via engineered materials. The lens is built from the patchy-particle interactions of S-crystallin proteins, which have a globular body and protruding, disordered loops that form the low-valence patches. A remaining mystery about the lens system is that the squid expresses over 40 distinct versions of S-crystallin. To understand what nature is telling us about realizing volume-spanning self-assembly, we studied the details of the S-crystallin patch geometry and interaction polydispersity on the percolation behavior and material properties of the system. We found that the low-valence particle geometry influences whether the system percolates or not, as well as the structure of the resulting gel. Further, we found that a distribution of patch energies (as realized by the many different S-crystallin sequences in nature) may facilitate the transparency of the system, by suppressing the growth of the correlation length at low densities and temperatures. |
Wednesday, March 8, 2023 9:00AM - 9:12AM |
M33.00006: Optimizing Pair Potentials for Efficient Crystallization Kinetics Sambarta Chatterjee, William M Jacobs We present an inverse-design algorithm to optimize an isotropic pair potential for kinetically efficient and thermodynamically stable self-assembly of a target crystal structure. In general, there is often a trade-off between kinetically and thermodynamically optimal pair potentials. Nonetheless, we show that applying a Fisher Information Metric-guided optimization algorithm "on the fly" - that is, concurrently with a simulated self-assembly process - identifies pair potentials that balance these two competing objectives. We specifically focus on assembling a honeycomb lattice, the two-dimensional analog of the diamond lattice, which is challenging to assemble due to the existence of competing crystal polymorphs at certain densities. Importantly, our approach requires no prior knowledge of the competing polymorphs and identifies optimal pair potentials on a time scale comparable to that of the kinetically optimized self-assembly process. Our results also suggest that time-dependent pair potentials proposed by our optimization approach can further enhance the self-assembly kinetics and avoid kinetic traps associated with competing polymorphs. |
Wednesday, March 8, 2023 9:12AM - 9:24AM |
M33.00007: Colloidal Model for the Study of Nucleation and Crystallization from Solution Gary Chen, Peter G Vekilov, Jacinta C Conrad Crystallization is a ubiquitous phenomenon that is important for materials in our daily life. Despite development of microscopic techniques, it is still challenging to observe crystallization processes at single molecule level due to temporal or spatial limitations. Thus, there remain fundamental open questions on how the interactions between monomers affect nucleation and growth from solution. Here, we study a model colloidal system as an alternative to atomic systems. The interactions between charged particles are tuned by screening the electrostatic repulsion and inducing depletion attractions with salt and non-adsorbing polyacrylamide, respectively. Analysis of the particle positions allow us to monitor the crystallization events. In quasi-2D experiments, clusters at a particular combined well-depth of ~2 kT are constantly rearranging during growth, and the fraction of crystal-like bonds increases non-monotonically. Solubility of the monomers at various conditions is determined and the thermodynamically-derived bond strength is in good agreement with our interparticle potential curve. Thus, we demonstrate a tunable colloidal system that is expected to provide insight into the mechanism of crystallization from solution. |
Wednesday, March 8, 2023 9:24AM - 9:36AM |
M33.00008: Direct Imaging of a Solid-Solid Phase Transition in Truncated Tetrahedral Colloids David Doan, John Kulikowski, Wendy X Gu Self-assembly of colloids crystal have been used to understand fundamental atomic dynamics such as disordering during melting and defect dynamics during applied stress. These types of systems have also been used to build meso-scale metamaterials with unqiue optical or mechanical responses. Although self-assembly of polyhedral colloids have predicted to form a variety of crystal structures, they have been challenging to fabricate chemically. Here, we use two-photon lithography to fabricate a subset of polyedral shapes (tetrahedrons and truncated tetrahedrons) that self-assembly on a 2D surface. We observe that truncated tetrahedrons assemble in a hexatic close-packed phase initally, and then transform into a quasi-diamond phase under additional graviational potential. Free energy calculations and Monte Carlo simulations reveal that supression of particle rotation is the main mechanism behind the initial hexatic phase, which is then unsupressed upon additional gravitational force. This mechanism is also confirmed by in-situ optical imaging of the phase transition at the single particle level. Our results demostrate the self-assembly of truncated tetrahedrons, with different assembly states controlled through particle rotation supression or activation by gravitational potentials. |
Wednesday, March 8, 2023 9:36AM - 9:48AM |
M33.00009: Probing 2D Phase Separation in Mixed Silica and Gold Nanoparticle Assemblies Zachary Fink, Paul Y Kim, Xuefei Wu, Thomas P Russell Interfacial assemblies of mixtures of different nanoparticles (NPs) can be used to obtain well-defined 2D phase separated morphologies that, by functionalization, generate surfaces with heterogeneous interaction sites. Yet, the kinetic pathways by which the 2D phase separation occurs are still poorly understood. We capitalize on nanoparticle surfactant (NPS) assemblies at a liquid-liquid interfaces to increase the binding energy of NPs to interfaces and to provide a platform for investigating densely packed, mixed silica(polystyrene) and gold NPSs by UV-Vis reflection spectroscopy and grazing incidence small angle x-ray scattering. Because the plasmon excitation energy depends on both the properties of individual gold NPs and the location and number of NPs in the ensemble, we can characterize the interparticle distances, degree of ordering, domain size, and structure of the NP assemblies. By tuning the size, number, and adsorption rate of each NP species in the assembly, we can control the morphology and kinetics that govern the phase separation and reveal structural correlations of larger gold NP clusters. We find that as inert NP concentration increases, the reduction rate of interparticle spacing decreases, are more ordered, and have smaller NP domains as the inert NPs act as barriers to intimate gold-gold contact. These complementary methods can be used to understand and control the nanoscopic factors that govern phase separation in two dimensions. |
Wednesday, March 8, 2023 9:48AM - 10:00AM |
M33.00010: Liquid Crystal-Templated Membranes with Slit-like Pores Homa Ghaiedi, Karthik Nayani, Jude Obijiaku We report on the formation of membranes with slit-like pores having aspect ratios ~ 10. Liquid crystals (fluids with orientational order) were used to template the membranes resulting in pores geometries that show a significant departure from conventional spherical shapes. Both the nematic-isotropic transition temperature of the templating liquid crystal and the glass transition temperature of the polymer influenced the membrane properties, including pore size, pore shape and membrane rigidity. Importantly, at the same reduced temperature of the LC/polymer-precursor mixture we were able to reproduce the membrane characteristics for a range of concentrations. |
Wednesday, March 8, 2023 10:00AM - 10:12AM |
M33.00011: Mesostructures and phase transition of imidazolium-based ionic liquid systems for training deep neural network algorithm Kyungtae Kim, Jacob A LaNasa, Darrick J Williams, Ben T Nebgen X-ray scattering data of ionic liquid (IL)/water mixtures were obtained and analyzed as training data sets for developing deep neural network (DNN) based computation architecture that can predict non-equilibrium, dynamical phenomena such as chemical reactions, self-assembly, and ionization. Specialized DNN based architectures are accurate and computationally efficient alternatives to the computationally expensive quantum mechanical simulations. But despite their broad applicability in chemical and materials discovery, they cannot describe non-equilibrium processes such as the long-range transfer of electron charge and finite electron temperature effects. ILs are known to form various hierarchical, mesoscale ordered structures when mixed with water, similar to the phase behavior of lyotropic liquid crystals. The hierarchical self-assembly of the ionic liquid systems is a complex phenomenon not easily predictable by computation. Thus, the IL/water mixtures is an excellent platform to produce large data set to train the DNN algorithm. Model systems of ILs, consisting of a cation having linear hydrocarbon tail and simple anions such as thiocyanate or nitrate, were mixed with varying amount of water to form mesoscale ordered structures and subsequently measured by X-ray scattering. The data was quantitatively analyzed by crystallographic methods and radial distribution function calculations. Potential implementation of the obtained data to DNN training will be discussed. |
Wednesday, March 8, 2023 10:12AM - 10:24AM |
M33.00012: Modeling Homo- and Heterogeneous Crystal Nucleation from Charged Colloids Sanjib Paul, Shihao Zhang, stefano sacanna, Glen M Hocky In this work, we performed molecular dynamics studies on the self-assembly of oppositely charged colloids in implicit water medium. Micrometer sized colloids interacting by a screened coulomb interaction, would aggregate irreversibly. A recent experimental work [Nature, 2020, 580, 487-492] showed that the neutral polymer brushes attached to the surfaces of the colloids can provide a repulsive interaction at close distances that prevents aggregation, and allows for the generation of ionic colloidal crystals, whose structures can be tuned via the particle size ratio and the solution salt concentration We previously employed a pairwise interaction potential that takes into account both the polymer brush and DLVO interaction potential to generate crystals consistent with those seen in experiment. Here, we study in more detail the effect of volume fraction and the salt concentration on the self-assembled structures. For a particular size ratio of the oppositely charged colloids, we observe a transition between the simple CsCl structure and various polymorphs that were not expected. Depending on the conditions, we find that nucleation can proceed via classical or non-classical pathways, which we are investigating in more detail. Finally, in our previous study, we employed a model of a charged wall to generate structures that were heterogeneously nucleated. Here we will investigate competition between homogeneous and heterogeneous nucleation pathways, which expand the range of polymorphs that can be observed within our simulations. |
Wednesday, March 8, 2023 10:24AM - 10:36AM |
M33.00013: An STDP-based encoding method for associative and composite data Hong-Gyu Yoon, Pilwon Kim Spike-timing-dependent plasticity(STDP) is a biological process of synaptic modification caused by the difference in firing order and timing between neurons. One of the neurodynamical roles of STDP is to form a macroscopic geometrical structure in the neuronal state space in response to a periodic input by Susman et al. (Nat. Commun. 10(1), 1–9 2019), Yoon, & Kim. STDP-based associative memory formation and retrieval. arXiv:2107.02429v2 (2021). In this work, we propose a practical memory model based on STDP which can store and retrieve high dimensional associative data. The model combines STDP dynamics with an encoding scheme for distributed representations and is able to handle multiple composite data in a continuous manner. In the auto-associative memory task where a group of images is continuously streamed to the model, the images are successfully retrieved from an oscillating neural state whenever a proper cue is given. In the second task which deals with semantic memories embedded in sentences, the results show that words can recall multiple sentences simultaneously or one exclusively, depending on their grammatical relations. |
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