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 W15: Simulation-based and Theoretical Insights into Polymer Physics |
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Sponsoring Units: DPOLY Chair: Jiale Shi, Massachusetts Institute of Technology Room: Room 207 |
Thursday, March 9, 2023 3:00PM - 3:12PM |
W15.00001: Simulations on Solution Assembly of Amphiphilic Grafting Polymers: from Comb to Bottlebrushes Yeojin Choe, Juhae Park, Abelardo Ramirez-Hernandez, Su-Mi Hur Amphiphilic polymers in solutions can be assembled into various structures like spheres, cylinders, bicontinuous, and vesicles, which are the core principle of many advanced nanotechnologies such as imaging, scaffolding, drug delivery, etc. Amphiphilic polymers with complex chain structures, such as grafting polymers, in which side chains are attached to a linear backbone, are expected to be feasible tools to create unprecedented structures or precisely control the type and size of structures. Here, we investigate the structures of grafting polymers of various grafting densities, side chain lengths, backbone lengths, and solvent quality using a coarse-grained simulation model, which describes the changes in the backbone flexibility induced by grafted side chains or interaction with solvents. We present our findings on the effects of chain architectures on micelle formations and their bending rigidity. |
Thursday, March 9, 2023 3:12PM - 3:24PM |
W15.00002: Molecularly informed field theoretic models of surfactant formulations My Nguyen, Kevin Shen, Nicholas Sherck, Stephan Koehler, Rohini Gupta, Kris T Delaney, M. Scott Shell, Glenn H Fredrickson Surfactants are an important class of materials and are widely used in industrial formulations including consumer care products. Their unique aqueous solution behavior stems from self-assembly and complexation, driven by an interplay of hydrophobic and electrostatic interactions. In this work, we present molecularly informed field theoretic models of formulations involving surfactants. We parameterize the field theoretic model from small-scale, atomistic simulations via the relative entropy coarse-graining framework. In a model mixture of surfactants and polyelectrolytes, we predict micelle and mesophase structure development as a function of composition (e.g., charge stoichiometry, ionic surfactant:nonionic surfactant ratio, and salt concentration) and provide new insights into existing experimental results. Furthermore, we demonstrate how these compositional parameters control the concentration at which micelles form, which in turn impacts surfactant interfacial activity. |
Thursday, March 9, 2023 3:24PM - 3:36PM |
W15.00003: Multiscale modeling of viscosity index improver (VII) polymers Charles Li, M. Scott Shell, Glenn H Fredrickson, Kris T Delaney Viscosity index improvers (VIIs) are compounds added to lubricants to help them maintain a uniform viscosity across a wide temperature range, allowing them to make important contributions to energy efficiency and wear protection. However, VIIs are typically high-molecular-weight polymers present at significant concentrations (~5 wt%), making them difficult to study using traditional particle-based simulation methods (e.g., all-atom or coarse-grained molecular dynamics) due to length and time scale limitations. To overcome this obstacle, we employ a workflow where small-scale, atomistic simulations are used to parameterize statistical field theory models, which can then be used to probe the behavior of VIIs of realistic sizes while maintaining a connection to the underlying chemistry. This multiscale computational approach has the potential to accelerate discovery of novel VIIs that have improved performance and are more environmentally friendly. We demonstrate the capability of this approach by predicting various thermodynamic properties, including critical micelle concentrations and phase transitions, of a model system consisting of acrylic copolymers in a model base oil. |
Thursday, March 9, 2023 3:36PM - 3:48PM |
W15.00004: Molecular-Dynamics Simulations of the Glass Transition in Hydrated Nafion Membranes Alexey Lyulin, Soumyadipta Sengupta, Anna Varughese, Pavel Komarov, Arun Venkatnathan Nafion is a commonly used polyelectrolyte membrane (PEM) in fuel cells and flow batteries. The annealing of polymer electrolyte membranes is known to affect the membrane structure and proton conductivity. The observed changes depend drastically upon the annealing temperatures and cooling rates. In this paper, we have performed a fully atomistic classical molecular-dynamics simulation of hydrated Nafion at various hydration levels and annealing rates. Our simulations [1] show the compression of hydrophobic Nafion domains by larger water clusters, with a strong antiplasticization effect upon hydration, demonstrated by increasing the glass-transition temperature. The close-range proximity of sulfonate−sulfonate groups of Nafion pendant side chains remains unchanged with the simulated cooling rates. The water clusters in hydrated Nafion become more disconnected and larger in size with slower cooling rates/increased annealing time. This results in the decrease of water and hydronium diffusivity and the corresponding conductivity, thereby explaining qualitatively the experimental observations. |
Thursday, March 9, 2023 3:48PM - 4:00PM |
W15.00005: Helical Wrapping of Carbon Nanotubes by Wormlike Chain Polymers Nigel T Andersen, Jeff Z Chen The helical wrapping of single walled carbon nanotubes (SWNTs) by long polymers is an interesting process, owing to the ability of some polymers to effectively solvate and separate individual nanotubes in solution without affecting their useful underlying electronic properties. Yet polymer behaviour at the nanotube surface remains poorly understood from a theoretical perspective. Although Monte-Carlo and molecular dynamics simulations have been carried out for individual polymer-nanotube combinations, and some approximate analysis has been done, there has not been a full theoretical study completed using a fundamental model over a large range of nanotube and polymer types. Here, we present an analysis of polymer statistics at the surface of the polymer-SWNT system using the standard wormlike chain (WLC) model. We calculate the expected helix pitch for a polymer wrapped SWNT over the full parameter space and compare to pitch measurements from 10 different studies in the literature. Good agreement is seen between our solution and the data over the full parameter range. Associated distribution functions are discussed. We conclude by calculating the exact scaling behaviour for small nanotubes, which we find agrees with expected behaviour for a tightly confined WLC system. |
Thursday, March 9, 2023 4:00PM - 4:12PM |
W15.00006: Spectral representation of sequence-defined polymers Oliver Xie, Bradley D Olsen The sequences of copolymers impact their microphase separation and lead to a variety of self-assembled structures. Manipulation of classical sequence descriptors such as Flory-Huggin interaction parameters or block fractions are known to open and close different regions of phase space. However, these descriptors are statistical; as polymer chemistry moves towards fully sequence-defined polymers, a complete description of sequence becomes defined at the limit of N degrees of freedom, where N is the number of monomers. This precludes efficient exploration of sequence space to target specific structures. In this talk, we show how a spectral representation of sequences presents a representation more amenable to uncovering fundamental links between sequence and structure. The degrees of freedom in a spectral representation describe the sequence on a global level; since structure is a global property, manipulation of spectral degrees of freedom might offer a more systematic way of conducting investigation into sequence space. We explore how attenuation of high frequency Fourier modes of a sequence through signal filters leads to similar phase behavior as the unmodified sequence. This congruence of behavior despite large changes in the sequence highlights how correlated changes in sequence may be necessary for preserving or changing ordered structure. |
Thursday, March 9, 2023 4:12PM - 4:24PM |
W15.00007: Computational Methods for Analysis of Small Angle Scattering Data from Polymer Networks Stephen Kronenberger, Arthi Jayaraman Polymer networks are a broad class of materials with applications in food science, chemical separations, and tissue engineering. The structure of a polymer network greatly impacts the macroscopic properties of the material, including mechanical properties and transport of fluids through the material. Small-angle X-ray and neutron scattering (SAXS and SANS) are techniques used to study the structure of polymeric materials at multiple length scales. Conventional analysis of scattering profiles involves extracting structural parameters by fitting an analytical model to the profile; however, the existing analytical models may be too approximate for unconventional structures accessed by novel polymer chemistries, creating a need for new analysis methods that do not rely on analytical model fits. The Computational Reverse-Engineering for Scattering Experiments (CREASE) algorithm is such a computational method. In this talk, we will present our ongoing work extending CREASE to provide structural information from scattering experiments of network structures. |
Thursday, March 9, 2023 4:24PM - 4:36PM |
W15.00008: Correlations in Hard- and Soft-Core Generic Polymer Models Qiang Wang Generic polymer models capturing the chain connectivity and the non-bonded excluded-volume interactions between polymer segments can be classified into hard- and soft-core models depending on their non-bonded pair potential. Here we compared the correlation effects on the structural and thermodynamic properties of the hard- and soft-core models given by the polymer reference interaction site model (PRISM) theory. The behavior of soft-core models at large invariant degree of polymerization depends on how it is varied, i.e., whether by changing the chain length N at fixed segment number density ρ (thus the excluded-volume interaction parameter ε is fixed) or by changing ρ at fixed N (thus ε is also varied as being inversely proportional to ρ). We also proposed an efficient numerical approach, which enables us to accurately solve the PRISM theory for N as large as 106. |
Thursday, March 9, 2023 4:36PM - 4:48PM |
W15.00009: Exploring the Density of States of Helical Homopolymer Systems Matthew J Williams The density of states of a system is an important tool that can be used to analyze the thermodynamic properties of a physical system. This talk will explore the use of the density of states and its derivatives to understand the structural transitions exhibited by a helical homopolymer model that will produce either long single-helix structures or folded two-helix bundles. The tertiary structure present in this system is dependent on the specifics of the model parameters chosen. Additionally, a two-dimensional density of states across energy and a structural order parameter will be used to demonstrate a dramatic difference in structure behavior for models which have similar densities of state. |
Thursday, March 9, 2023 4:48PM - 5:00PM |
W15.00010: Analyzing Anisotropic Structure in Soft Materials from Small Angle Scattering Profiles Nitant Gupta, Arthi Jayaraman Structural anisotropy can be found in nature, for example in tissues, or in synthetic soft materials with anisotropic building blocks (e.g., liquid crystals) and/or upon being processed (e.g., extrusion). Characterizing the structural anisotropy in the three-dimensions can be quite complicated and requires sophisticated imaging techniques like tomography or cryogenic-transmission electron microscopy. Small angle scattering techniques can therefore be used to analyze three-dimensional structure over multiple length scales. The information pertaining to anisotropy requires the interpretation of 2D scattering profiles, for which analysis methods to extract extent of orientational order are often limited. Previous work in our group led to the development of 'Computational Reverse Engineering Analysis for Scattering Experiments' (CREASE) method to identify relevant length-scales in isotropic structures and reconstruct their three-dimensional structure. In this talk we will demonstrate the steps we have taken to extend CREASE to analyze 2D scattering profiles and quantify a) the distribution of sizes and shapes of anisotropic structural elements (i.e., building blocks or domains they form) and b) orientational and positional ordering of these structural elements within the soft material. |
Thursday, March 9, 2023 5:00PM - 5:12PM |
W15.00011: Influence of Photo-induced bond-breaking and bond-formation on phase separation kinetics polymeric fluids: DPD simulation insights Awaneesh Singh We study the phase separation dynamics of block copolymer (BCP) melt in d=3 using the dissipative particle dynamics (DPD) simulation method. The system is subjected to external stimuli such as light. A homogeneously mixed BCP melt is rapidly quenched below the critical temperature, and we let the system go through alternate light “on” and “off” cycles. An on-cycle breaks the stimuli-sensitive bonds connecting blocks A and B in BCP melt, and broken bonds reconnect during the off-cycle. The variation in bond breaking rate constant mimics an impression of variation in light intensity. By simulating the effect of light, we isolate scenarios where phase separation begins with the light off (set 1); the cooperative interactions within the system allow it to undergo microphase separation. When the light is on (set 2), the system undergoes macrophase separation due to the bond breaking. Here, we report the role of alternate cycles on domain morphology by varying bond-breaking probability for both sets. We observe that the scaling functions depend upon the conditions mentioned above that change the time scale of the evolving morphologies in various cycles. The average domain size respects the power-law growth: R(t) ~ tΦ at late times for all the cases, where Φ is the dynamic growth exponent. However, the effect of bond-breaking on the separation kinetics becomes more noticeable up to the system passing through the first light-on cycle. |
Thursday, March 9, 2023 5:12PM - 5:24PM |
W15.00012: Open-source Code for Langevin Field-Theoretic Simulation Daeseong Yong, Wonjun Kang, Jaeup Kim We provide an open-source Langevin field-theoretic simulation (L-FTS) for the block copolymer (BCP) field-based simulations. L-FTS is one of the partial saddle point approximation methods that can account for the compositional fluctuation effect, which is neglected in the self-consistent field theory (SCFT). By parallelizing the computations using the GPU, we achieved a 20x speedup in typical BCP systems compared to the CPU implementation. Our open-source code is provided as a library for Python programming language, so that one can implement SCFT calculation and L-FTS by writing a Python script. This allows L-FTS to be integrated with numerous useful Python libraries. We implemented deep learning boost of the L-FTS on top of this library and is also publicly available, which provides additional 6x speedup without compromising accuracy. |
Thursday, March 9, 2023 5:24PM - 5:36PM |
W15.00013: "Chemical transistor" effect in two-dimensional amine-functionalized graphene oxide membranes Siyu Chen Selective membranes with preferential transport of specific substances have attracted wide research interests over the past years for ion extraction and wastewater treatment. Graphene oxide membrane with 2D transport channels exhibits fast water transport and effective sieving effect, but its ability of ion-ion selectivity, especially for those with similar size and charge, is relatively limited. Here, we developed a layer-by-layer structure with NH3+ binding sites based on multilayered graphene oxide and polyethylenimine membrane and focused on the permeation mechanism of four anions: Cl-, NO3-, SO42-, and PO43-. The membrane shows excellent selectivity for Cl-. Although Cl- and NO3- have similar size and charge, the permeation of Cl- is four times faster than that of NO3- due to their distinct structure configurations and hydration properties. These Cl--selective binding sites exhibit ultrahigh selectivity of Cl- to SO42- and PO43- in both binary and quaternary anion mixtures, which are 11 and 39 (binary) and 12 and 17 (quaternary) respectively. The density functional theory calculations reveal that Cl- has a lower energy barrier to overcome when hopping through the binding sites. The permeation of the impermeable ions could also be adjusted by the addition of Cl-, showing the chemical transistor effect. The combination of graphene oxide and polyethylenimine demonstrates a successful strategy to construct selective membranes based on the interactions between ions and the transport channel for the agriculture industry and wastewater treatment. |
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