Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session Z17: Responsive Polymers, Soft Materials, and CrystallizationFocus Recordings Available
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Sponsoring Units: DPOLY DSOFT Chair: Matthew Green, Arizona State University Room: McCormick Place W-184BC |
Friday, March 18, 2022 11:30AM - 12:06PM |
Z17.00001: An Introduction to Mechanophores: Utilizing Mechano-Responsive Molecules for Stress Visualization Invited Speaker: Chelsea S Davis Mechanophores (MPs) are a class of stimuli-responsive materials that are of increasing interest to engineers due to their potential applications as stress sensors. A wide array of applications that require continuous structural health monitoring could benefit from MPs including flexible electronics, protective coatings, and polymer matrix composites. This talk will introduce MPs to a broad audience and then share some of our recent work in the calibration and implementation of these molecular damage sensors in a variety of polymeric systems. First, we investigate the role of interfacial strength on the stress field developed in the matrix of a glass/polymer composite. Here, we utilize a mechanically-activated fluorescent dye molecule (MP) to visualize stress gradients around a rigid inclusion upon mechanical deformation. By coupling our experimental observations of mechanophore activation with finite element analysis of the various stress states that develop in the loaded composite, a novel approach to quantitatively calibrate the MP fluorescent activation intensity has been established. We then apply our calibration to several test cases of silica/silicone composites with dramatically different levels of interfacial strength. This mechanophore/mechanical deformation approach enables stress fields to be observed in a powerful new way via fluorescence imaging in a mechanically loaded polymer network. Next, we employ MPs to demonstrate the overlapping stress fields in a polymer matrix as two rigid reinforcement particles are placed in close proximity to one another in a deformed composite. Finally, we employ progressive loading scratch via nanoindentation to highlight the utility of MPs as a defect detection tool in transparent polymer coatings. |
Friday, March 18, 2022 12:06PM - 12:18PM |
Z17.00002: Simulations of Failure in Mechanically Active Triblock Copolymers Stephen J Skala, Zijian Huo, Jennifer E Laaser, Antonia Statt Mechanochemically active materials have emerged as an attractive platform for diverse applications in polymeric materials, including strain sensing, chemical catalysis, and self-healing properties. Understanding how bulk forces are transmitted on the molecular level is vital in the field of mechanochemistry in order to develop materials with targeted mechanochemical properties. Triblock ABA copolymers offer an attractive platform for controlling mechanochemical activation via their nanostructure. We have previously shown, through molecular dynamic simulations, that the mechanical activation in these systems is highly dependent both on the chain configuration and the morphology. However, the model we used did not exhibit brittle failure mechanisms as seen in experiments of the same material. To address the shortcoming of the model, we have introduced a modified Lennard-Jones potential into the previously used coarse-grained model with force-sensitive mechanophore units. By measuring activation and chain conformations, we aim to determine the mechanophore activation and materials response to different microscopic failure mechanisms. |
Friday, March 18, 2022 12:18PM - 12:30PM |
Z17.00003: Computational Design of Bottlebrushes of PNIPAM-Dextran Copolymers Sanket A Deshmukh, Soumil Y Joshi, Parisa Farzeen In the present study, we have performed coarse-grained (CG) molecular dynamics (MD) simulations of bottlebrush polymers (BBPs) of dextran and poly(N-isopropylacrylamide) (PNIPAM) copolymers. PNIPAM is a thermosensitive polymer with a lower critical solution temperature (LCST) of 305 K, below and above which it is soluble and insoluble in water, respectively. Dextran is a water-soluble, biodegradable neutral bacterial exopolysaccharide consisting of repeating glucose subunits. PNIPAM-dextran copolymers and their star-like architectures have already shown potential for various biomedical applications including universal platform for drug delivery. The worm-like and cone-like BBPs of PNIPAM-dextran copolymers with variations in the lengths of PNIPAM and dextran in side-chains and their grafting densities on the BBP backbone were generated. The CG MD simulations of these BBPs were performed below and above LCST of PNIPAM. The analysis of CG MD trajectories performed by using data driven machine-learning (ML) methods to unravel the dependence of metastable states on the side-chain length, grafting density, and temperature. Our research provides guidance in designing novel BBPs of PNIPAM-Dextran Copolymers. |
Friday, March 18, 2022 12:30PM - 12:42PM |
Z17.00004: Dynamics of stable contact formation bewteen a nanoparticle and a highly repulsive polymer layer Sai A Etha Assembling nanoparticles inside a polymer brush layer is crucial in developing new hybrid materials. Depending on the application, these materials may require a combination of nanoparticle and polymer with weak interaction strengths. We use molecular dynamics simulations to study the assembly and dynamics of nanoparticles in a grafted polymer layer in the presence of a favorable solvent. The presence of the favorable solvent ensures a stable interaction of the nanoparticle with the polymer brush independent of the nanoparticle-polymer interaction strength and the size of the nanoparticle. For strong nanoparticle-polymer interactions, the nanoparticle remains completely inside the polymer layer while for weak interactions, the nanoparticle mostly remains adsorbed on the surface of the brush. |
Friday, March 18, 2022 12:42PM - 12:54PM |
Z17.00005: The Effect of Morphology on Mechanical Activation in Nanostructured Triblock Copolymers Zijian Huo Mechanochemistry has emerged as an attractive approach for driving constructive chemical transformations in responsive polymeric materials. However, understanding how the polymer structure influences the molecular force distribution in bulk materials under mechanical load remains a challenge. Here, we investigate the effect of polymer morphology on mechanochemical activation in nanostructured triblock copolymers. We synthesize a series of force-responsive block copolymers (PMMA-b-PnBA-SP-PnBA-b-PMMA) containing a force-sensitive spiropyran unit at the center of the rubbery midblock, with varying lengths of the glassy end-blocks to achieve different well-ordered morphologies. We compare the mechanochemical activation behaviors of the polymers using simultaneous tensile tests and optical measurements, and show that the mechanochemical activation is strongly correlated to the chemical composition and morphologies of the block copolymers, with increasing glassy block content driving activation of the mechanophore at lower strain. These findings demonstrate that self-assembly of nanostructured morphologies is a viable route to controlling mechanochemical activation in polymeric materials, and provide insights into how such nanostructuring impacts molecular-scale force distributions in these materials. |
Friday, March 18, 2022 12:54PM - 1:06PM |
Z17.00006: Temperature dependent photoisomerization kinetics of semicrystalline poly(azobenzene)s Hantao Zhou, Ryan C Hayward Among the variety of photomechanical materials studied to date, photoresponsive semicrystalline polymers provide a potential route to enhance performance by combining a high degree of molecular ordering of polymer crystallites with facile material processing and actuator fabrication. However, the regular packing of azobenzene units within the crystalline lattice can hinder the trans-cis isomerization, a process which requires a substantial amount of free volume, thus deteriorating the photomechanical performance. We have studied the temperature-dependent kinetics of photoisomerization in poly(azobenzenes) with both alkyl and ethylene glycol chain extenders. Interestingly, while the amorphous component switches readily in both cases, the former polymers show a dramatic decrease in rate for the crystalline phase near room temperature. Understanding these temperature dependent photoisomerization kinetics is expected to enable control of photomechanical response time-scales, improve the energy efficiency of photo-actuation. |
Friday, March 18, 2022 1:06PM - 1:18PM |
Z17.00007: Understanding Shape Manipulation of Polymer Vesicles: a Reactive Dissipative Particle Dynamics Study Qinyu Zhu, Douglas R Tree Biological cells have long been of interest to researchers due to their ability to actively control their shape. However, the complexity of the process makes it hard to define a deterministic mechanism. Therefore, there is significant interest in mimicking similar behaviors in simplified synthetic systems such as polymer vesicles. Accordingly, we have developed a custom reaction-diffusion model that combines Dissipative Particle Dynamics (DPD) and the Split Reactive Brownian Dynamics (SRBD) that can model the dynamic self-assembling of polymers as they undergo chemical reactions, which expands the capability of simulating the non-equilibrium stochastic behavior of polymer solutions on mesoscopic scales. We first use reactive dissipative particle dynamics (RDPD) to investigate the local shape change driven by either an enzymatically-produced stimulus or microinjection of a stimulus. Our model predicts localized inflation that is induced by either a solvent stimulus that swells the vesicle, or a reactant stimulus that alters the chemistry of the block polymer. Having established this foundation, we use our RDPD simulations to further investigate mechanisms that can induce more complex shape changes and catalytically-driven motion of polymer vesicles. |
Friday, March 18, 2022 1:18PM - 1:30PM |
Z17.00008: Light-Responsive, Reversibly Shape-Changing Block Copolymer Particles using Photo-Switchable Au Nanoparticle Surfactants Seung Ho Kwon, Meng Xu, Jinwoo Kim, Eun Ji Kim, Young Jun Lee, Se Gyu Jang, Hongseok Yun, Bumjoon J Kim Dynamic particles with switchable shapes in response to light have attracted great interest to develop smart materials with superior spatial and temporal resolution. Herein, a facile strategy for light-responsive, shape-changing block copolymer (BCP) particles is developed. We designed the azobenzene-grafted Au (Au@Azo) nanoparticles as photo-switchable surfactants through photoisomerization of Azo ligands. Under visible light, onion-like polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) BCP particles with PS outer layers form due to the non-polar nature of trans-Azo ligands, whereas the isomerization to polar cis-Azo with UV irradiation transforms to ellipsoids with both PS and P2VP exposed on their surfaces. This light-driven shape change is fully reversible over multiple irradiation cycles. The reversible shape evolution between spherical and ellipsoidal BCP particles induced by photo-active Au@Azo surfactants is elucidated using a cryogenic electron microscope. Furthermore, light-dependent fluorescence and shape of the BCP particle is successfully demonstrated, enabling the visualization of particle shape into an optical signal. |
Friday, March 18, 2022 1:30PM - 1:42PM |
Z17.00009: Micellar structures of chain end functionalized oligo(dimethyl siloxane) Kunlun Hong, Tianyu Li, Yingdong Luo Abstarct: Polymers modified with a functional group, including chain end functionalization, can vary its morphologies and properties drastically. Chain end transformation is a well-established technique and such technique has been applied to a wide range of polymers. We recently exploited the using of oligo(dimethyl siloxane) (ODMS) functioned with an ionic liquid group to mimic lipid membranes and studied their structures at liquid/air and liquid/liquid interfaces.1,2 In this contribution, we report micellar structures of ODMS functionalized with different charged groups in solutions. Dynamic light scattering (DLS) and small angle X-ray scattering (SAXS) revealed the roles of the counter ionic and solvent on the structures and stabilities of the micellar structures. These results help us design better polymeric materials for mimicking lipid membranes and neuromorphic networks. Reference:
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Friday, March 18, 2022 1:42PM - 1:54PM |
Z17.00010: Application of Raman Spectroscopy to Determine the α Phase Crystalline Fraction in Poly(vinylidene fluoride) Films Anuja S Jayasekara, Peggy Cebe Poly (vinylidene fluoride), PVDF, is a semi-crystalline polymorphic polymer with three stable crystallographic forms. The non-polar alpha phase with TGTḠ chain conformation is the most common crystal form found in PVDF. α phase crystals can be obtained by cooling from the melt at conventional cooing rates of ~10-100 °C/min. We prepared PVDF films by compression molding PVDF (Kynar 301F) at 200ºC and cooling under ambient conditions. Fourier transform infrared spectra (FTIR) spectroscopy confirmed that only α-phase crystals were formed. By application of an annealing heat treatment, the crystalline fraction in the samples was varied from 38% to 65%. The application of Raman spectroscopy to determine the crystalline fraction of α-PVDF is novel. In this study, the degree of crystallinity of α-PVDF determined by Raman spectroscopy is presented and compared to the crystalline fraction found both from thermal analysis of endotherm area and from wide-angle X-ray scattering. |
Friday, March 18, 2022 1:54PM - 2:06PM |
Z17.00011: Rheological investigation of partially crystallized polymer melts Marat Andreev, Gregory C Rutledge, Anthony Kotula, Jaap den Doelder, Jonathan Moore Modern molecular-based rheological models for polymer melts connect molecular weight distribution, long-chain branching distribution, and rheology. Unfortunately, they are typically limited to completely molten polymers, whereas the arrangement of crystalline and amorphous domains is primarily responsible for the mechanical properties of semi-crystalline polymers. Molecular architecture affects the development of crystallites along with the material's rheology as a semi-crystalline polymer crystallizes. |
Friday, March 18, 2022 2:06PM - 2:18PM |
Z17.00012: Nanoscale technologies to study life sciences - from neurochemical imaging to agricultural biotechnology Markita P Landry Unique physical, chemical, and optical phenomena arise when materials are confined to the nanoscale. We are accustomed to making observations and predictions for the behavior of living systems on a macroscopic scale that is intuitive for the time and size scales of our day-to-day lives. However, the building blocks of life: proteins, nucleic acids, and cells, occupy different spatiotemporal scales. Our lab focuses on understanding and exploiting tunable optical and mechanical properties of nanomaterials to access information about biological systems stored at the nanoscale. In the context of leveraging nanomaterial optical properties, we present recent work on developing and implementing neuromodulator nanosensors to image serotonin or dopamine volume transmission in the extracellular space of the brain. We validate our dopamine nanosensor in acute striatal slices with electrical and optogenetic stimulation of dopamine release and show disrupted dopamine release or reuptake kinetics when brain tissue is exposed to dopamine agonist or antagonist drugs. In the context of leveraging nanomaterial chemical properties, we also discuss how high aspect ratio nanomaterials can be synthesized to carry biomolecular cargo to living systems. In particular, genetic engineering of plants is at the core of environmental sustainability efforts, but the physical barrier presented by the cell wall has limited the ease and throughput with which exogenous biomolecules can be delivered to plants. We describe how nanomaterials engineering principles can be leveraged to genetically manipulate living plants, without transgene integration, in efforts to reconcile the benefits of crop genetic engineering with genome editing tools. Our work in the agricultural space provides a promising tool for species-independent, targeted, and passive delivery of genetic material, without transgene integration, into plant cells for rapid and parallelizable testing of plant genotype-phenotype relationships. |
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