Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session V08: Polymer Structure Formation and Dynamics in Solution II: Chain Conformations and Phase SeparationFocus Live
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Sponsoring Units: DPOLY GSNP DBIO Chair: Xiaodan Gu, University of Southern Mississippi |
Thursday, March 18, 2021 3:00PM - 3:12PM Live |
V08.00001: Phase Behavior of Polymer-Grafted Nanoparticles Amalie Frischknecht, Jason Koski, Andrew Santos A common strategy to control nanoparticle (NP) distribution in composites is to graft polymer chains onto the NP surfaces. Grafted polymer NPs can exhibit rich phase behavior due to complex interplays among chain conformational entropy, depletion effects, and enthalpic interactions. We use theoretically-informed Langevin dynamics (TILD) simulations to determine the structure of polymer brushes on single grafted NPs and to calculate equilibrium phase diagrams in solution. For NPs grafted with two immiscible polymers, the polymers microphase separate on the surface of the particle. A Janus structure is obtained for sufficiently small NPs, while the polymers grafted to larger NPs tend to form disordered patchy structures on the NP surface. Janus-patterned NPs self-assemble in solution into interesting aggregates such as vesicles. I will also discuss phase diagrams for NPs grafted with homopolymer and dispersed in solvent. |
Thursday, March 18, 2021 3:12PM - 3:24PM Live |
V08.00002: The Bulk Phase Behavior of Ternary Mixtures of Polymers and Two Good Solvents Xiangyu Zhang, Jing Zong, Dong Meng Mixed solvents are extensively utilized in diverse processes for characterizing, separating, and assembling polymers. However, understanding the thermodynamics of these polymer solutions remains rudimentary. One example is the so called cononsolvency effect, under which polymers in a good solvent undergo reentrant coil-to-globule-to-coil transition upon addition of a good cosolvent. Only recently, computer simulations have clarified the generic nature of the effect. Yet, the phase behavior of the solutions associated with such effect remains uncharacterized. In this study, we combine the self-consistent field (SCF) calculations and the Gibbs-ensemble simulations that employ identical models to determine the binodal curves of ternary mixtures of polymers and two good solvents. It is found that adding a small amount of cosolvent to solution can induce a 1st-order phase separation. The coexisting densities predicted by the SCF calculations matches those from the simulations, pointing to the leading role of the mean-field density correlations in such polymer cononsolvency behavior. A transition back to the homogeneous phase is observed as the cosolvent composition further increases that is predicted to be of 1st-order in the SCF but appears as a 2nd-order transition in simulations. |
Thursday, March 18, 2021 3:24PM - 3:36PM Live |
V08.00003: Shear-Sensitive Chain Extension of Poly(ethylene oxide) by Aluminate Ions During Concrete Curing David Hoagland, Satyam Srivastava, Zachary Fink, Thomas P Russell, Elizabeth Burns Despite a large literature, questions about PEO’s interactions with ions remain. Motivated by PEO’s potential to reduce CO2 emissions as a strength-building concrete additive, its conformation was examined in solutions containing complex ions found during concrete curing. Conformational changes in most electrolytes were unremarkable, hydrodynamic radius by dynamic light scattering and intrinsic viscosity depressed slightly as ion concentrations grew. Trends were different for aluminum-containing ions [at neutral and basic pH, predominately the monovalent hydroxoalmuminate anion Al(OH)4], hydrodynamic radius by the two methods disagreeing: radius by dynamic light scattering was approximately 40% larger than by intrinsic viscosity. We hypothesize weak, attractive ion-mediated chain-chain interactions, and in particular, a weak coupling between hydroxyl end groups (at just one PEO chain end) disrupted by the shearing during intrinsic viscosity measurements. Supporting our hypothesis, hydrodynamic radius by dynamic light scattering fell to the value by intrinsic viscosity when the groups were converted to methoxy groups. The role, if any, of the coupling in concrete curing is unknown. |
Thursday, March 18, 2021 3:36PM - 3:48PM Live |
V08.00004: Helical Persistence Length of Poly-L-Lysine Kathryn Wilcox, Marlee Dingle, Svetlana Morozova In order to understand the role of α-helical flexibility in protein function, we investigate the helical and electrostatic contributions to the persistence length (lp) of poly-L-lysine (PLL) independently by inducing a coil-helix transition by changing the pH, and probing the electrostatic effects by changing the solution ionic strength. Using static and dynamic light scattering, lp is determined from the salt- and pH-dependent Rg. In addition to Rg, hydrodynamic radius, (Rh), the shape factor (Rg/Rh), and second virial coefficient (A2) of the PLL for a range of salt and pH conditions are reported. In neutral pH, the polymer is a random coil, swollen by charge interactions. Increasing the ionic strength reduces the polyelectrolyte lp and increases chain flexibility due to greater salt screening. Increasing the pH leads to the partial and complete formation of helices and dominance of the helical contribution to lp, which leads to an increase in rigidity, but not to the extent predicted by molecular dynamics simulations. By understanding the contributions to helical lp, we can further understand their implications to protein flexibility and function. |
Thursday, March 18, 2021 3:48PM - 4:00PM Live |
V08.00005: Kinetics of xanthan in denaturation and renaturation process in dilute aqueous NaCl solution Yu Tomofuji, Ken Terao, Koichi Matsuo Denaturation and renaturation processes of xanthan in 5 mM or 10 mM aqueous NaCl were investigated with abruptly heated from 20 to 80 °C or quenched from 80 to 20 °C by using small-angle X-ray scattering (SAXS) and circular dichroism (CD) measurements. The time-development of CD signal took place more rapidly than that of the SAXS profile in denaturation process, while the SAXS intensity changed much more rapidly than the CD data in the renaturation process, indicating that the conformation of the side chain changes more rapidly than the melting of the double helical structure in the denaturation process. In contrast, the formation of double helical structure is faster than the orientation of the side chain in the renaturation process, while the CD spectra after 24 h were identical to the original solution, suggesting that the conformation of side chain after renaturation is the same as the native state. Our research suggests that the slow deformation and rapid recovery of ordered structure of the main chain may contribute to maintain the functionality derived from the polymer conformation. |
Thursday, March 18, 2021 4:00PM - 4:12PM Live |
V08.00006: Ion jacket regulates flexible biopolymer conformation in salt mixtures Sarah Innes-Gold, David Reid Jacobson, Philip Pincus, Mark J Stevens, Omar A. Saleh Polysaccharides, proteins, and single-stranded nucleic acids are biologically important flexible polyelectrolytes (PEs). Due to their charge and flexibility, their conformations are usually very sensitive to ionic strength. Prior work has characterized how PE stiffness scales with 1:1 salt, but biological solutions contain multiple ion species and valences. In those cases, PEs are affected by an interplay of strong electrostatics (leading to multivalent ion condensation) and weaker long-range screening, but it is not known how this will manifest in the chain stiffness. We use single-molecule magnetic tweezers to measure three biological PEs in various salt mixtures. We observe a surprising regime in which a small amount of multivalent salt eliminates the effect of ionic strength. Simulations reveal an “ion jacket” layer of condensed multivalent cations and loosely associated monovalent ions, in which an ion exchange process protects against changes in bulk ionic strength. A model that relies on local Donnan equilibrium rather than Debye screening predicts salt-dependent ion condensation that accounts for the insensitivity. This unexpected regime where charge-renormalized chains ignore ionic strength has implications for both in vivo biopolymer structure and biomaterials design. |
Thursday, March 18, 2021 4:12PM - 4:24PM Live |
V08.00007: Characterizing Synthetic Random Heteropolymers through Simulation Shayna Hilburg, Ting Xu, Alfredo Alexander-Katz Synthetic random heteropolymers have complex properties that make them capable of interfacing favorably with proteins and mimicking biomolecular systems. Atomistic molecular dynamics simulations allow the investigation of these random heteropolymers assembled in solution at the nanoscale, bridging the gap between angstrom-scale NMR and bulk characterization. Here, we present the impact of composition, molecular weight, and solvent environment on a single-chain methacrylate-based synthetic heteropolymer system. Our findings show that while a wide variety of individual sequences exist in a random heteropolymer system, their physicochemical properties are dominated by the overall compositions and monomer arrangements that arise from the synthesis process, making their properties generally tunable. The detailed understanding of the effect of composition and environment on polymer behavior we provide enables heteropolymer design for a variety of polymer nanoparticle applications. |
Thursday, March 18, 2021 4:24PM - 4:36PM Live |
V08.00008: Decoupling conjugated polymer’s backbone and sidechain conformation by selective deuteration and neutron scattering Zhiqiang Cao, Zhaofan Li, Song Zhang, Luke Galuska, Tianyu Li, Changwoo Do, Wenjie Xia, Kunlun Hong, Xiaodan Gu Conjugated polymers (CPs) with high optoelectronic performance are of paramount interest to industrial applications. Specifically, experimental characterization of conjugated polymer backbone conformations remains underexplored due to limited techniques that can distinguish the backbone and sidechain structures. Thus, relating the electronically functional backbone conformation to the material’s macroscopic optoelectronic property is an ongoing challenge. Here, small-angle neutron scattering techniques (SANS) with contrast variation (CV) experiments are employed on CPs (poly(3-alkylthiophenes) (P3ATs) and diketopyrrolopyrrole (DPP) based polymers). We obtained the form factor of P3ATs’ backbone, sidechains, and cross scattering term by deconvoluting their respective scattering signals. The strong scattering signal from long and flexible alkyl sidechains leads to a seemingly more rigid conjugated polymer. This work offers a methodology to decouple the scattering contribution from the CPs’ backbone and sidechains, thus elucidating the inherent conformation of the electronically active conjugated backbone. |
Thursday, March 18, 2021 4:36PM - 4:48PM Live |
V08.00009: Designing Bottlebrush Additives with Polyfluoropolyether (PFPE) Sidechains: Focus on Bottlebrush Architecture and Effects of Solvent Quality Sidong Tu, Chandan Kumar Choudhury, Liying Wei, Igor Luzinov, Olga Kuksenok Molecular bottlebrushes are rapidly becoming a material of choice for a plethora of applications, ranging from electronic and photonic materials to thermal stabilization of enzymes. Our experimental studies show that addition of only a minute fraction of bottlebrushes with polyfluoropolyether (PFPE) sidechains results in a dramatic improvement of oleophobicity of polymer matrix. PFPE has a low surface energy and is of interest because it is non-toxic and environmentally friendly due to its chemical inertness. We develop a coarse-grained model of this amphiphilic bottlebrush using dissipative particle dynamics (DPD) approach and validate our model with respect to the prior molecular dynamics simulations and experimental studies. We focus on dynamics of phase separation and self-assembly of clusters of bottlebrushes in the solvents of various quality and in various polymer matrices. We characterize domain growth dynamics and evolution of cluster aggregation in the polymer matrix/bottlebrush/solvent system. We show that clusters sizes, morphologies, and shape anisotropies are controlled by the bottlebrush architecture and affinities between all the moieties within the system. |
Thursday, March 18, 2021 4:48PM - 5:00PM Live |
V08.00010: Coarse-grained Simulations of Poly (ethylene oxide) Linear Chains and Catenanes in dilute solutions Jiuke Chen, kun qian, Mesfin Tsige Poly (ethylene oxide) (PEO), known as Polyethylene glycol (PEG) at low molecular weight, is an important petrochemical product that has abundant applications in industry and medicine. Therefore, it is important to understand the effect of PEO topology on its physical properties in solutions. Computational simulations can give detailed properties at the micro-level. Many Monte Carlo simulations have been performed for coarse-grained Poly (ethylene oxide) (PEO) linear chains and catenanes in the melt. Here, we report Molecular dynamics (MD) simulation results on the structural and dynamical properties of PEO linear chains and catenanes in dilute solutions. The MARTINI force field is applied and the interaction between PEO of different topologies with a select group of solvents is also investigated. The numerical results are compared with literature results from all-atom simulations and also with bead-spring model simulation results from our own group. |
Thursday, March 18, 2021 5:00PM - 5:36PM Live |
V08.00011: Entropy Driven Assemblies in Dilute Solution Invited Speaker: Ting Xu There have been numerous studies using well-defined blends to recapitulate hierarchical assemblies using DNA, peptide, protein, block copolymer, supramolecule as well as colloids. The work can be divided into two camps to the first approximation, those using precise intra- and inter-molecular interactions and those using entropy-driven phase behavior. However, the exact origin of system diversity and complexity, which are abundant in natural system such as cell wall, cytosol, and any given body fluids, remains mysterious. I will describe a recent studies showing that chemical diversity and complexity can enhance system miscibility such that entropy-driven phase behavior can be realized in composites. |
Thursday, March 18, 2021 5:36PM - 5:48PM Live |
V08.00012: Structure-property relationships of branched polyethylene in dilute solution Robert Ivancic, Chase Thompson, Sara V Orski, Debra Audus While branched polyethylene is ubiquitous in technological applications, structural characterization of these polymers remains a challenge. Commercial separations of polyethylene often contain a mixture of linear, short-chain branched, and long-chain branched polymers that have overlapping hydrodynamic sizes and solubility making it difficult to determine the underlying mixture components. Here, we perform molecular dynamics simulations using an experimentally inspired potential to study the structure-property relationships of branched polyethylene in the dilute regime. In particular, we calculate experimentally accessible properties such as the hydrodynamic radius, radius of gyration, and intrinsic viscosity. When possible, we compare our results directly to experiments of linear low-density polyethylene in which branch spacings and lengths are precisely controlled and systematically varied. |
Thursday, March 18, 2021 5:48PM - 6:00PM Live |
V08.00013: Nitroxide Radical Polymer-Solvent Interactions and Solubility Parameter Determination Alexandra Easley, Lillian M Vukin, Paraskevi Flouda, Dylan L Howard, Jose L Pena, Jodie Lutkenhaus Redox-active polymers such as macromolecular nitroxide radicals have been studied as electrode materials for organic batteries and electronics. Polymer−solvent interactions are essential to processing and device performance, but macromolecular nitroxide radical−solvent interactions are currently not well described. In this talk, the Hildebrand and Hansen solubility parameters of poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl methacrylate) (PTMA) and oxidized PTMA (PTMA+) will be discussed from both experimental and group contribution methods. From these solubility parameters, the group contribution values for the nitroxide and oxoammonium cation were then calculated. It is shown that this information allows for the prediction of polymer−solvent interactions for other nitroxide-based macromolecular radicals. Finally, the discovered solubility parameters are used to predict PTMA electrode formulations for batteries that outperform controls. |
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