Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session K17: Dillon Medal SymposiumFocus Prize/Award Recordings Available
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Sponsoring Units: DPOLY Chair: Andy Spakowitz, Stanford University Room: McCormick Place W-184BC |
Tuesday, March 15, 2022 3:00PM - 3:36PM |
K17.00001: John H. Dillon Medal Award (2022): Toward quantitative modeling of polyelectrolyte complexation Invited Speaker: Jian Qin Recent activities in polyelectrolyte complexation (PEC) have been spurred by the advancements in theoretical descriptions of polyelectrolytes, and by the need to control PEC behavior in a wide range of applications. The basic principles behind PEC are well understood. However, quantitative PEC models have not achieved the same accuracy as models for neutral polymer solutions. A survey of new theoretical and experimental developments on thermodynamics of PEC suggests that electrostatic interactions, though not the only important factor, are essential for successful modeling of PEC. We show that the modern molecular theory for polyelectrolytes captures PEC behavior calibrated from carefully designed experiments. The effects of backbone polarity and mixing stoichiometry are presented as examples. An unexpected reentrant behavior revealed in non-stoichiometric solutions is highlighted, and is shown to originate from the interplay of the entropy of neutralizing counter-ions and the strength of electrostatic correlations. Finally, some open questions on accurate PEC modeling are discussed. |
Tuesday, March 15, 2022 3:36PM - 3:48PM |
K17.00002: Modeling the microemulsion channel in ternary mixtures of AB diblock copolymer with A and B homopolymers David C Morse, Mridul Yadav Ternary mixtures of symmetric AB diblock copolymer and A and B homopolymers exhibit a microemulsion channel in which a strongly correlated disordered phase remains stable over a narrow range of copolymer compositions, where it competes with a highly swollen lamellar phase. We discuss an attempt to model this behavior in a manner inspired by older membrane models of the microemulsion phase in small molecule oil-water-surfactant mixtures. In this approach, we model the free energy of the disordered phase by combining a self-consistent field theory description of a surrogate ordered network with entropic corrections that account for topological entropy and renormalization of the Gaussian rigidity by interfacial fluctuations, and allow for the effect of undulation-induced steric repulsion on the stability of the competing lamellar phase. |
Tuesday, March 15, 2022 3:48PM - 4:00PM |
K17.00003: Aging Resistant Toughness in Poly(lactide) Charles McCutcheon, Christopher J Ellison, Boran Zhao, Frank S Bates, Kailong Jin Poly(lactide) is a leading sustainable polymer derived from corn. Both glassy, poly((+/-) lactide) (PLA), and semicrystalline (PLLA) versions of this material suffer from physical aging, whereby the plastic, which is ductile immediately following thermal processing, becomes mechanically brittle after approximately one day of annealing at room temperature. Blending 5 wt% of a disordered poly(ethylene oxide)-block-poly(butylene oxide) (PEO-PBO) diblock copolymer (Mn = 7.4 kg/mol; 35 vol% PEO) with commercially available PLA and PLLA results in a dramatic increase in ductility, which persists after annealing for more than 100 days at room temperature. This behavior is attributed to the formation of a stable morphology during melt blending consisting of ~0.8 micron diameter particles of PEO-PBO, which cavitate and initiate crazing during tensile deformation. We speculate that the relatively low molecular weight block copolymer rapidly diffuses from the liquid droplets into the crazes, plasticizing the surfaces and fibrils, thereby inhibiting brittle fracture. Similar property improvements were obtained with uniaxially strained films of these toughened sustainable plastics. |
Tuesday, March 15, 2022 4:00PM - 4:12PM |
K17.00004: Measuring the packing length in polymer simulations Scott T Milner Predicting the entanglement length in melts and solutions from single-chain properties has been a longstanding challenge in polymer physics. It has been understood for some time that bulky, flexible chains entangle differently than skinny, stiff chains. For bulky flexible chains, other chain segments are prevented from approaching more closely than the packing length, and entanglement properties are described by Lin-Noolandi scaling. For skinny stiff chains, other segments can approach within a chain diameter, and entanglement is described by Morse scaling. Recent progress has unified these regimes, and focused attention on measuring the packing length, defined by the typical distance of close approaches, rather than by a scaling estimate of limited applicability. By measuring entanglement properties and the packing length for a family of bead-spring chains of different bulkiness and flexibility, we observe Lin-Noolandi scaling where it should be valid. More recently, we have applied the technique of measuring the packing length to all-atom simulations of real polymer melts, and compared our values to those inferred from experimental data and Lin-Noolandi scaling, with promising results. |
Tuesday, March 15, 2022 4:12PM - 4:24PM |
K17.00005: Emerging AI-enhanced approaches for polymer design Juan De Pablo The ability to generate large data sets from experiments and simulations, coupled to the development of new machine learning algorithms, is leading to significant changes in polymer physics reasearch. In this work, I will discuss these advances in the context of two examples. In the first, large data sets from simuations are used to train neural networks for prediction of polymer properties as a function of monomer sequence and chemical characteristics. In the second , large data sets from simulations are combined with machine learning to predict the long-time relaxation of microphase separated polymeric materials. |
Tuesday, March 15, 2022 4:24PM - 4:36PM |
K17.00006: Polymer electrolytes in heterogenous media Monica Olvera De La Cruz, Trung D Nguyen, Felipe Jimenez-Angeles Polyelectrolytes control the organization and properties of materials with important applications in bio- and nano-technology including energy storage and therapeutics as well as protein delivery and compartmentalization. In this talk, we reveal the effect of ionic correlations and dielectric mismatch on the structure and properties of polymer electrolytes in confinement. |
Tuesday, March 15, 2022 4:36PM - 4:48PM |
K17.00007: Increased Donnan Exclusion at High Salt Concentrations Kevin W Gao, Xiaopeng Yu, Nitash P Balsara The swelling of charged polymeric networks in electrolytic solutions were first modeled by Donnan, who derived an expression for the chemical potential of the ions by introducing an electric potential that is commonly referred to as the Donnan potential. This well-established theory leads to a simple quadratic relationship for the partitioning of ions between the network and the external solution. When the concentration of fixed charges in the swollen gel is large enough, the electrolyte in the external solution is "excluded" from the gel (commonly referred to as Donnan exclusion). In the standard Donnan theory, and in virtually all subsequent theories, the magnitude of Donnan exclusion decreases with increasing electrolyte concentration in the external solution. We will discuss experiments and physical models wherein the magnitude of Donnan exclusion increases with increasing electrolyte concentration. |
Tuesday, March 15, 2022 4:48PM - 5:00PM |
K17.00008: Enhancing ion transport in charged block copolymers by stabilizing low symmetry morphology Moon Park We show the enhancement of ion transport properties for charged block copolymers comprising non-stoichiometric ionic liquids by stabilizing the cubic Frank-Kasper A15 phases with space group Pm3n. The ionic liquid cations predominantly present near the micellar interfaces to increase stabilization energies of the A15 structures if they have strong attractive electrostatic interactions with the charged polymer chains. Unprecedented re-entrant phase transitions between lamellar and A15 structures occur through the electrostatic control of interfaces. Overall, the stabilization energies of the A15 structures were greater when enriched, attractive electrostatic interactions were present at the micellar interfaces. Contrary to the conventional wisdom that block copolymer interfaces act as “dead zone" to significantly deteriorate ion transport, this study establish a prospective avenue for advanced polymer electrolyte having tailor-made interfaces. |
Tuesday, March 15, 2022 5:00PM - 5:12PM |
K17.00009: Coarse-Grained Modeling of Ion Mobility and Conductivity in Block Copolymers Lisa M Hall, Mengdi Fan, Yuanhao Zhang Microphase separating copolymers are of interest as safe, nonflammable battery electrolytes because one microphase can solvate and allow transport of ions while the other provides mechanical strength. Motivated by the large design space of possible polymer architectures and polymer and ion chemistries, along with the need to improve ion transport properties, we study a range of related materials through generic coarse-grained simulations. The strong solvation of ions in the higher dielectric constant polymer (conducting phase) is captured using an ion-monomer potential of the same form as the interaction between an ion and an induced dipole (-S/r4). We also use the dielectric constant of the conducting phase to set the Coulomb interaction strength, as the large majority of ion interactions occur in that microphase. This model reproduces experimentally observed trends in lamellar domain spacing and ion conductivity versus ion concentration. We apply this model to systems with small amounts of added conducting-type homopolymer, and find that this can improve ion mobility, especially near the center of the conducting phase. Initial analysis of local and overall ion transport for systems with anions tethered to the chains will also be discussed. |
Tuesday, March 15, 2022 5:12PM - 5:24PM |
K17.00010: Quantifying the effects of intra-domain structure and dynamics on ion transport in nanostructured block polymer electrolytes Thomas H Epps Nanostructured block polymer electrolytes can boost the performance and safety of lithium-ion batteries relative to liquid electrolytes. However, the presence of interfaces between microphase-separated domains can introduce complexities in the local ion transport, as competing effects (e.g., interfacial segmental mixing vs. chain stretching) can increase or decrease local mobility. We present a quantitative framework to account for the effects of polymer architecture, segmental mixing, chain stretching, and confinement on the dynamics of polystyrene‑block‑poly(oligo-oxyethylene methacrylate) (PS-b-POEM) electrolytes, and we validate this framework through nuclear magnetic resonance spectroscopy measurements on solid‑state electrolyte samples. Notably, we found that a mobility-onset temperature that captures the heterogeneous dynamics along the POEM side chain is a better predictor of segmental mobility than the POEM thermal glass transition temperature. Additionally, our framework explains the mobility gradient across a domain when we combine segmental mixing effects with chain stretching and confinement information, especially at the higher segregation strengths. This quantitative link between local and global dynamics can facilitate the design of next‑generation electrolytes. |
Tuesday, March 15, 2022 5:24PM - 5:36PM |
K17.00011: Modeling the Phase Behavior of Complex Coacervates formed from Polyelectrolytes and Surfactant Micelles Charles E Sing, Jason Madinya Oppositely-charged macromolecular species can undergo an associative phase separation, in a process known as complex coacervation. There has been significant interest in coacervation between two polyelectrolytes, however for many biological and industrial applications coacervation occurs between species where at least one of the components is not a linear polymer. This includes coacervates driven by charged proteins, colloids, or surfactant micelles. In this talk, we will show how we use a hybrid simulation and field theory calculation to capture the physics of liquid-liquid phase separation in polymer-surfactant micelle coacervates. This method is an extension of the transfer matrix approach developed by the authors. We demonstrate the importance of charge correlations between strongly-charged micellar surfaces, and we map out the phase behavior of these polyelectrolyte-surfactant micelle coacervates upon varying the strength of these correlations, the polyelectrolyte chain length, and micelle size surface charge density. We demonstrate qualitative agreement with experimental literature, and show that a coexistence exists between micelle-dilute and micelle-dense phases reflects a competition between charge correlations and micelle excluded volume. |
Tuesday, March 15, 2022 5:36PM - 5:48PM |
K17.00012: Polyelectrolyte Complex Materials Sarah L Perry Polyelectrolyte complexation can be used in the self-assembly of a wide range of responsive, bioinspired soft materials ranging from dehydrated thin films, fibers, and bulk solids to dense, polymer-rich liquid complex coacervates. While the phase behavior of liquid-liquid phase separated complex coacervates has been studied for many years, our understanding of how factors like polymer chemistry alter the physical properties of the resulting coacervates is less well developed. Furthermore, a number of reports take advantage of coacervates as a processable liquid phase for fabricating solid films, fibers, etc. upon removal of salt. For these materials, it is an open question as to how the properties of liquid coacervates translate to those of a solid polyelectrolyte complex, and the role that polymer chemistry might play in these systems. We harness model copolymer systems to explore the ways in which polymer chemistry (e.g., backbone chemistry, charge group, neutral comonomers) and physical parameters such as length affect the mechanical response of both liquid and solid complexes, with an eye towards developing these materials for a range of future applications. |
Tuesday, March 15, 2022 5:48PM - 6:00PM |
K17.00013: A new computational method CREASE to analyze and interpret small angle scattering profiles from polymers and soft materials Arthi Jayaraman In this talk I will present the Computational Reverse Engineering of Scattering Experiments (CREASE) method that we have developed to analyze small angle scattering profiles and interpret assembled structure in macromolecular solutions. There are two steps within CREASE: the first step involves a genetic algorithm (GA) to determine the shape and dimensions of the domains in the assembled structure and the second step uses molecular simulations to reconstruct chain conformations and monomer level arrangements within the assembled structure. We validate the GA step within CREASE by taking input scattering intensity profiles from a variety of assembled shapes with known shapes and dimensions, and by producing outputs that match those known shapes and target dimensions. CREASE’s power lies in its ability to interpret structural detail at a range of length scales for macromolecular solutions without relying on fitting with off-the-shelf analytical models that may be too approximate for novel polymers and/or unconventional assembled structures. |
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