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 M03: Programmed Responsive Polymers and Soft Matter IFocus
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Sponsoring Units: DPOLY Chair: Jinhye Bae, University of California, San Diego Room: Room 126 |
Wednesday, March 8, 2023 8:00AM - 8:12AM |
M03.00001: Osmotic Swelling Behavior and Structure of Ionic Microgel Mixtures Mohammed O Alziyadi, Alan R Denton Microgels are soft, compressible colloidal particles composed of crosslinked polymer networks. When dispersed in solution, microgels absorb solvent and can acquire charge by dissociation of counterions. Importantly for applications (e.g., drug delivery, biosensing), particle swelling responds to environmental changes (e.g., temperature, pH, concentration) and interparticle interactions. Introducing polydispersity in equilibrium size and charge of microgels can greatly enrich bulk properties. Within a coarse-grained modeling framework [1-3], we derive effective electrostatic interactions in binary mixtures of ionic microgels that carry fixed charges on their surfaces. We model steric interactions between microgels via Hertz elastic pair potentials and swelling via Flory-Rehner theory of polymer networks. Inputting density-dependent effective interactions into Monte Carlo simulations, we compute equilibrium swelling ratios, radial distribution functions, and static structure factors of microgel solutions. We show that swelling behavior and structural properties are sensitive to polydispersity, expanding possibilities for controlling self-assembly and guiding design of novel materials. |
Wednesday, March 8, 2023 8:12AM - 8:24AM |
M03.00002: Folding of Biopolymers in Crowded Environments Mahesh Aryal, Alan R Denton Accurately modeling folding and predicting native structures of biopolymers (e.g., proteins, RNAs, DNAs) are grand challenges. Theories of folding suggest that proteins explore metastable intermediate states before arriving at the global minimum energy state [1]. Furthermore, folding behavior in biological cells is profoundly influenced by macromolecular crowding. We perform molecular dynamics simulations of coarse-grained models of proteins that are predicted to follow either two-state or multi-state folding pathways and explore how conformational stability and folding pathways depend on crowder properties, e.g., sizes, concentrations, and interparticle interactions. From probability distributions of the eigenvalues of the gyration tensor in the principal axis reference frame, we determine the radius of gyration and shape of proteins in intermediate states, with and without crowding agents. The main concept is that the gyration tensor can serve as a predictor of the intermediate states of a protein and can distinguish different kinetic folding pathways. To validate our approach, we also simulate random-walk homopolymers in crowded solutions and compare against known shape distributions [2]. |
Wednesday, March 8, 2023 8:24AM - 8:36AM |
M03.00003: Sequence Control of Bioinspired Calcium-Responsive Protein Polymers Marina P Chang, Danielle J Mai Ion-responsive polymers have broad applications ranging from tissue engineering to actuation in soft robotics. Calcium responsiveness emerges in a class of "Repeats-in-Toxin" (RTX) proteins that undergo reversible conformation changes from random coils to β-roll structures upon binding to calcium. RTX proteins are characterized by the repetitive sequence GGXGXDXUX, in which glycine (G) and aspartic acid (D) are highly conserved in the calcium-binding region. For positions that are less conserved, U represents an aliphatic amino acid and X represents any amino acid. We explored monomer-scale manipulations of this sequence by creating a panel of RTX proteins with substitutions at the fifth position in the GGXG(X)DXUX sequence. These amino acid substitutions probe the impact of monomer size, electrostatic interactions, and hydrophobicity on the calcium-responsive behavior of RTX proteins. RTX proteins exhibit distinct structures and sizes in the presence versus absence of calcium ions, as characterized by circular dichroism, dynamic light scattering, and small angle X-ray scattering. Broadly, RTX proteins provide a programmable platform to tune calcium responsiveness in polymeric materials. |
Wednesday, March 8, 2023 8:36AM - 8:48AM |
M03.00004: Phase behavior of pH-responsive polyelectrolytes and hydrogels Tine Curk, Jiaxing Yuan, Erik Luijten Polyelectrolytes and hydrogels in solution acquire charge through the dissociation or association of ionic surface groups. Thus, a proper description of their electrostatic interactions requires the use of charge-regulating boundary conditions rather than the commonly employed constant-charge approximation. Using a Monte Carlo/molecular dynamics scheme that dynamically adjusts the charges of individual ionizable groups we calculate pH–temperature phase diagrams of linear polyelectrolytes as well as hydrogels. Using histogram reweighting techniques we uncover that charge regulation effects lead to, respectively, discontinuous coil–globule and collapse–swelling transitions. The extent of the discontinuous region and the existence of two critical points at low and high pH values depends sensitively on the size of the counterions. Computational results are supported by an analytical mean-field theory. These insights are used to design efficient hydrogel-based nano-actuators. |
Wednesday, March 8, 2023 8:48AM - 9:24AM |
M03.00005: Rational Heteropolymer Design Based on Protein Sequence Space Invited Speaker: Ting Xu In contrary to well accepted protein sequence-structure-function relationship, random heteropolymers (RHPs) embrace controlled randomness as a critical design parameter to access protein-link behaviors. We hypothesize that proteins' segmental sequence information can guide statistic sequence control in RHPs to holistically replicate protein functions. I will discuss our recent efforts to translate protein sequence information into RHP design. Specifically, we extracted the chemical characteristics and sequential arrangement along a protein chain from natural protein libraries and used the information to design heteropolymer ensembles as protein mimics. Experimentally, the level of segmental similarity to that of natural proteins determines its ability to replicate proteins' multiple functions. Molecular studies further translated protein sequence information at the segmental level into intermolecular interactions with a defined range, degree of diversity, and temporal and spatial availability. This framework provides valuable guiding principles to synthetically realize protein properties, engineer bio/abiotic hybrid materials, and ultimately, realize matter-to-life transformations. |
Wednesday, March 8, 2023 9:24AM - 9:36AM |
M03.00006: Architecturally Semiflexible Bottlebrush-Based Block Copolymers Liheng Cai, Shifeng Nian For block copolymer (BCP) self-assembly, classical understanding is that domain spacing is limited by the contour length of the polymer backbone. We discover that this molecular picture does not hold for architecturally semiflexible block copolymers. For strongly segregated linear–semiflexible bottlebrush–linear triblock copolymers, the bottlebrush can rearrange its constituent linear side chains to form domains remarkably larger than the contour length of the bottlebrush backbone. Moreover, the semiflexible bottlebrush widens the regime for the cylinder morphology that is associated with the volume fraction of the end blocks fCSFB ∈ (0.10, >0.41), much wider than that for flexible linear BCPs, fCF ∈ (0.14, 0.35). Further, we propose a modified Halpin-Tsai model to describe the shear modulus G of polymers with cylinder morphology:G = Gm(1+ζf)/(1–f), in which Gm is the shear modulus of bottlebrush matrix and ζ is an adjustable parameter that describes the grain size relative to the fiber diameter.. Our results not only reveal previously unexplored molecule-structure-property relation of self-assembled bottlebrush polymer networks, but also provide a new class of soft, solvent-free, and reprocessable polymeric materials with a wide range of controllable stiffnesses. |
Wednesday, March 8, 2023 9:36AM - 9:48AM |
M03.00007: Long-range correlations and yielding of diblock star-polyelectrolyte micelles in the diluted limit Andrea Giuntoli, Roshan A Yunus, Aleksander Guzik, Utku Gürel, Marc C Stuart, Patrizio Raffa, Daniele Parisi We report a combined study of the synthesis, rheology, electron microscopy, and molecular dynamics of four-arm diblock poly(styrene) (PS) – poly(methacrylic acid) (PMAA) star polymers in solution. The stars assemble into spherical micelles with a ~10nm PS core and a ~100nm highly charged PMAA outer block which is almost completely stretched in the limit of low salt concentration. Linear rheology shows a liquid-to-solid transition at a mass concentration as low as 0.25 wt.%, while simulations show a threefold decrease of the effective radius of the micelles in the 0.1-1% concentration range. These results are consistent with a picture of ultrasoft colloids with large and highly tunable caging effects at extremely low concentrations. Additionally, the system presents a non-vanishing elastic modulus (from rheology) and a peak of the radial distribution function (from simulations) even in the dilute regime limit, caused by the long-range repulsion between the micelle corona. The micelle size and caging behavior are extremely sensitive to changes in pH or the addition of oppositely charged polymers forming the basis for a class of tunable soft colloidal glasses. |
Wednesday, March 8, 2023 9:48AM - 10:00AM |
M03.00008: Acousto-Photolithography for Programmable Shape Deformation of Composite Hydrogel Sheets Jinhye Bae, Minghao Li, Jiyang Mei, James Friend Stimuli-responsive hydrogels with programmable shapes produced by defined patterns of particles are of great interest for the fabrication of small-scale soft actuators and robots. Patterning the particles in the hydrogels generally requires external magnetic or electric fields, thus limiting the material choice for the particles. However, acoustically driven particle manipulation depends on the acoustic impedance difference between the particles and the surrounding fluid, making it a more versatile method to spatially control particles. Here, we introduce the combination of acoustic force to align photothermal particles and photolithography to spatially immobilize these alignments within a temperature-responsive poly(N-isopropylacrylamide) hydrogel to trigger shape deformation under temperature change and light exposure. The spatial distribution of particles can be tuned by the power and frequency of the acoustic waves. Specifically, changing the spacing between the particle patterns and position alters the bending curvature and direction of this composite hydrogel sheet, respectively. Further, this acousto-photolithography provides a means of spatiotemporal programming of the internal heterogeneity of composite polymeric systems. |
Wednesday, March 8, 2023 10:00AM - 10:12AM |
M03.00009: Structure-dependent mechanoluminescence behaviors via 3D printing of capillary suspensions Jiayu Zhao, Seongkyu Song, Xuan Mu, Soon M Jeong, Jinhye Bae Mechanoluminescence (ML) materials have received considerable attention due to their ability to transform mechanical stimuli into optical signals. However, the potential of ML devices has not been fully leveraged as restricted by the relatively simple geometry design, which inherently limits the programmability of the luminescence behaviors and mechanical properties. Here, we present a design strategy and fabrication technique for creating well-defined periodic cellular 2D or 3D ML devices with tunable mechanical properties and structure-depended ML behavior (i.e., anisotropic and isotropic luminescence). A granular ink formulation consisting of zinc sulfide (ZnS)-based phosphors and elastomer precursors is developed to enable 3D printing by taking advantage of the capillary state. The quantitative structure-stress-luminescence relationship is further studied, which provides fundamental knowledge support for designing next-generation ML-based stress sensors and wearable devices. |
Wednesday, March 8, 2023 10:12AM - 10:24AM |
M03.00010: Nanostructured Block Polymer Muscles Exhibiting Reversible Actuation Robert J Hickey Advances in functional soft material actuators that contract, expand, or rotate when triggered with an external stimulus are necessary to realize the future of new robotic assemblies with superior biologically relevant functions. Current research efforts are focused on synthesizing new soft materials to mimic natural muscles from a performance perspective, but neglect the impact of chemical composition and structure hierarchy, which are core features for the exceptional actuation properties of human muscles. Here, the presentation will cover a new class of fiber actuators that contract or rotate when triggered by heat or hydration. The fibers are produced by combining solution-phase block copolymer self-assembly and strain-programmed crystallization. The strained fibers consist of highly aligned nanoscale structures with alternating crystalline and amorphous domains, resembling the ordered and striated pattern of mammalian skeletal muscles. The nanostructured block copolymer muscles exhibit exceptional actuation properties, outperforming many current polymer actuators. The presentation will cover the nanoscale self-assembly mechanism during straining that gives rise to the actuation properties and the structural changes that occur during contraction. |
Wednesday, March 8, 2023 10:24AM - 10:36AM |
M03.00011: Simulating soft matter self-assembly using deformable nanoscale building blocks Vikram Jadhao, Fanbo Sun, Lauren Nilsson Most computational studies of soft matter assembly focus on coarse-grained models which employ rigid building blocks that do not exhibit shape adaptation during the self-assembly. We study the self-assembly of elastic building blocks using the virus capsid system as an example. A coarse-grained model of protein subunits that incorporates their stretching and bending energies is developed while retaining many features of the rigid-body models including a truncated pyramid shape favorable to icosahedral capsid assembly. Molecular dynamics simulations show that flexible protein subunits can reproduce the rich assembly diagram associated with the T1 Minute Virus of Mice (MVM) system including fully-formed 20-subunit capsids, kinetically-trapped disordered structures, and non-assembled configurations. In addition to traditional control parameters such as steric attraction between proteins and salt concentration, the model enables the study of using elasticity as a knob to change assembly behavior. The pronounced effects of changing protein flexibility on the capsid assembly and assembly-competent pathway products are discussed. |
Wednesday, March 8, 2023 10:36AM - 10:48AM |
M03.00012: Finite element modeling of hydrogel swelling under arbitrary confinements Chaitanya S Joshi, Jean-Francois Louf, Sujit S Datta, Timothy J Atherton Hydrogels are polymer networks that have an incredible capacity to absorb water while remaining intact. This makes them amenable to a variety of different practical applications. Due to the inevitable involvement of shape change, continuum modeling of hydrogels is often restricted to simple geometries. Incorporating constraints presents further challenges. In this work, we present a finite element model of hydrogel swelling in the presence of arbitrary impenetrable confinements, written in Morpho, an open-source programmable environment for shape optimization. We demonstrate the versatility of our approach by investigating a variety of different confinements and analyze the swelling ratios as well as the internal stress-strain variations resulting from them. |
Wednesday, March 8, 2023 10:48AM - 11:00AM |
M03.00013: Effect of Photoisomerizable Surfactant on Light-Responsive Shape Transformation of Block Copolymer Particles Jinwoo Kim, Bumjoon J Kim, Kang Hee Ku Photoactive shape-changing particles offer a promising platform for smart materials with tunable properties at high spatiotemporal resolutions. Herein, a series of spiropyran (SP)-based surfactants with different alkyl spacer lengths are developed to achieve photoactive, shape-changing PS-b-P4VP particles from the evaporative emulsion. The length of the alkyl chain spacer between the SP head group and ionic chain end is modulated from hexyl to ethyl decanoate to provide surfactants with tunable amphiphilicity. Under UV light, the hydrophilic merocyanine surfactants produce onion-like microspheres with a P4VP surface. Conversely, exposure of visible light yields striped ellipsoids with axially stacked PS and P4VP blocks. This shape transition is only observed for surfactants that contain spacers longer than or equal to octyl. The effects of photoswitchable surfactants on their interfacial properties and the corresponding morphological evolution of the particles are investigated to elucidate the shape transition mechanism. Finally, the shape- and color-switchable BCP particles are integrated to form a composite hydrogel, demonstrating their potential as high-resolution displays with reversible patterning capabilities. |
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