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 F63: Padden Award SymposiumLive Prize/Award
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Sponsoring Units: DPOLY Chair: Mahesh Mahanthappa, University of Minnesota |
Tuesday, March 16, 2021 11:30AM - 11:42AM Live |
F63.00001: All-Atom Molecular Dynamics Simulations of the Temperature Response of Densely Grafted Polyelectrolyte Brushes Harnoor Sachar, Bhargav Chava, Turash Pial, Siddhartha Das Polyelectrolytes (PEs) are large molecules formed by a combination of charged repeating units. PE chains can form a “brush”-like structure when end-grafted to a surface in close proximity of each other. Such PE brushes have been utilized in a wide variety of applications such as current rectification, drug delivery, colloidal stabilization, etc. due to their ability to respond to environmental factors such as pH, solvent quality, and temperature. We use all-atom Molecular Dynamics (MD) simulations to probe the effect of temperature on several structural and dynamical properties of water-swollen PE brushes such as the brush height, hydrogen bonding, counterion solvation structure, tetrahedral order parameter of the water molecules as well as the mobility of the brush-supported water and counterions. Our results indicate a reduced mass density of the trapped water molecules and an enhanced replacement of the counterion solvation water with PE functional groups at elevated temperatures, thereby promoting “water-in-salt”-like behaviour (with the counterions acting as the cations and the PE brush repeating units acting as the anions of the salt). |
Tuesday, March 16, 2021 11:42AM - 11:54AM Live |
F63.00002: In Situ Monitoring Polymer Imbibition in Nanopores by Nanodielectric Spectroscopy Chien-Hua Tu, Hans-Juergen Butt, George Floudas The question of how polymers penetrate narrow pores (2D confinement) is relevant in several applications (e.g. inkjet printing). In this study, the construction of a nanofluidic method capable of following the details of polymer imbibition in situ is explored. The method provides simultaneous access to the kinetics of imbibition, the molecular dynamics and the viscosity experienced by the polymer during flow. Two particular systems have been investigated. One is based on the highly polar poly(n-butyl methacrylate) (PnBMA) and the other on the relatively apolar cis-1,4-polyisoprene (PI). The former (PnBMA) provided information of the segmental dynamics and of the imbibition length during flow facilitating a stringent test of the Lucas-Washburn equation applicable to Newtonian fluids. With respect to PI, results showed that polymer imbibition proceeds in two time-regimes with higher effective viscosity than in bulk. In a recent publication [C.-H. Tu et al. Phys. Rev. Lett. 125, 127802, 2020] we discussed this finding with the help of a microscopic picture that considers the competition from an increasing number of chains entering the pores and a decreasing number of fluctuating chains with time. The latter provided unambiguous evidence for increasing adsorption sites during flow. |
Tuesday, March 16, 2021 11:54AM - 12:06PM Live |
F63.00003: Coupled effects of concentration and chain architecture on non-equilibrium polymer solution dynamics Charles Young, Yuecheng Zhou, Charles M Schroeder, Charles E. Sing The dynamics of semidilute polymer solutions are of practical importance to soft materials. Strong flows during coating and printing processes result in non-equilibrium polymer conformations that ultimately control material properties. Despite their practical importance, we have not yet achieved a complete molecular-scale understanding of non-dilute polymer solutions due to a complex interplay of interpolymer and hydrodynamic interactions (HI) that are challenging to characterize and expensive to simulate. In this work, we develop an understanding of the combined effects of concentration, chain architecture, and flow using a new simulation method that enables rapid and efficient simulation of non-dilute polymer solutions with long-range HI. Using this approach, we study the dynamics of semidilute ring-linear polymer blends at concentrations 0.1-3.0 c* in planar extensional flow. In contrast to pure polymer solutions, ring-linear blends exhibit unique conformational dynamics. Importantly, our results highlight the prevalence of strong ring-linear topological constraints and large conformational fluctuations due to local flow instabilities. These results are consistent with single-molecule observations of labeled linear and ring DNA chains in semidilute solutions. |
Tuesday, March 16, 2021 12:06PM - 12:18PM Live |
F63.00004: Molecular origin of strain-induced chain alignment in PDPP-based semiconducting polymers Song Zhang, Amirhadi Alesadi, Mariia Selivanova, Wenjie Xia, simon Rondeau-Gagne, Xiaodan Gu Due to the heterogeneous structure and complex solid-state morphology of Donor-acceptor (D-A) type semiconducting polymers, their complete molecular picture under deformation is hard to detect. Here, we probed the molecular orientation of free-standing D-A polymer thin films under tensile alignment, based on a diketopyrrolopyrrole (DPP) polymer. The detailed morphological analysis demonstrates highly aligned polymer crystallites through in-plane rotation towards the strain direction, while the backbone's alignment within the crystalline domain is limited. Surprisingly, the overall chain anisotropy is still low under large deformation. These observations are distinct from traditional semicrystalline polymers like polyethylene due to extinct characteristics of backbone, side-chain, and crystallites in DPP polymers. This study deconvolutes the alignment of multiple components in the polymer microstructure and highlights that crystallite rotation and amorphous chain slippage are the primary chain alignment mechanisms for semiconducting polymers. |
Tuesday, March 16, 2021 12:18PM - 12:30PM Live |
F63.00005: Percolated aggregates in precise sulfophenylated polyethylenes: Designing pathways to facilitate proton and ion transport Benjamin Paren, Bryce Thurston, Manuel Maréchal, Arjun Kanthawar, Justin G Kennemur, Mark J Stevens, Amalie Frischknecht, Karen Winey We present a set of precise, ring-opening polymerized, single-ion conducting polymers that self-assemble into percolated aggregates. These aggregates serve as pathways for rapid proton conductivity in the hydrated state (proton exchange membrane) and transport metal cations in the anhydrous state (solid polymer electrolyte). These polymers consist of a polyethylene backbone with a sulfonated phenyl group pendant on every 5th carbon. We study this polymer in the pure acid form (p5PhSA) under hydrated conditions and fully neutralized by different counterions (p5PhSA-X, X+=Li+, Na+, or Cs+) in anhydrous conditions, using X-ray scattering, electrical impedance spectroscopy, and atomistic molecular dynamics (MD). In hydrated p5PhSA, the polymer backbone nanophase separates from the percolated acid/water domain, through which the protons travel. p5PhSA has proton conductivity of 0.28 S/cm at 40°C and 95% relative humidity, exceeding that of Nafion. The dry p5PhSA-X polymers form fully percolated ionic aggregates, and have metal cation transport decoupled from the glassy polymer backbone up to at least 180°C. This behavior results from the percolated nature of p5PhSA (-X) and demonstrates the potential of precise polymers to effectively form pathways for facilitating transport. |
Tuesday, March 16, 2021 12:30PM - 12:42PM Live |
F63.00006: Sol-gel transition of loopy polymer networks Tzyy-Shyang Lin, Rui Wang, Bradley Olsen During the crosslinking of telechelic polymer chains into a network, the system undergoes a competition between bridging and looping reactions. Looping events not only significantly impact the mechanical properties (e.g. modulus and tearing energy) of the resulting network, but also severely influence the kinetics of the emergence of the giant component (i.e. the gel). While the mechanism by which loops delay the onset of gelation has been largely established, the impact of looping events on the criticality of the sol-gel transition has not been studied as comprehensively. To date, the analogy between gelation and percolation is still largely the standard framework for understanding the gelation process of loopy networks, even though loops introduce irregularities in network topology as well as inhomogeneous rates of bond formation that render the percolation model not directly applicable to the real gelation process. To address this, we utilize a kinetic Monte Carlo simulation that accurately accounts for the loop-bridge competition to numerically track the sol-gel transition. It is found that when looping events are introduced, the criticality of the sol-gel transition can be significantly impacted, as demonstrated by a change in the apparent percolation critical exponents. |
Tuesday, March 16, 2021 12:42PM - 12:54PM Live |
F63.00007: Direct Observation of Block Copolymer Micelle Fragmentation Julia Early, Alison Block, Kevin G. Yager, Timothy Lodge Block copolymers (BCPs) self-assemble into various micellar nanostructures in block selective solvents, which can be applied in a host of diverse technologies including drug delivery, viscosity modification, and nanoreactor design. To fully realize these practical uses, the mechanisms for BCP micellization and equilibration must be elucidated. Micelle fragmentation, fusion, and chain exchange are all possible relaxation mechanisms. Fragmentation has not been studied in detail. We use temperature-jump dynamic light scattering (T-jump DLS), synchrotron small-angle X-ray scattering (SAXS), and liquid-phase transmission electron microscopy (LP-TEM) to develop a quantitative understanding of micelle fragmentation kinetics in ionic liquids (ILs). Fragmentation of 1,2-polybutadiene-b-poly(ethylene oxide) was observed for various molecular weights in one IL using LP-TEM. The fragmentation kinetics were studied with time-resolved SAXS and T-jump DLS. By combining these experimental techniques, a detailed analysis of micelle fragmentation kinetics, along with the direct observation of intermediate structures during fragmentation events, was conducted. |
Tuesday, March 16, 2021 12:54PM - 1:06PM Live |
F63.00008: Revisiting packing frustration and strong-segregation stability of double-gyroid in block copolymer melts Abhiram Reddy, Gregory M Grason Formation of double gyroid(DG) in self-assembled block copolymer(BCP) melts, along with understanding molecular-scale mechanisms behind its equilibrium selection, has been a topic of longstanding interest in polymer physics. In this talk, we will revisit equilibrium DG in strong segregation limit(SSL) using parabolic brush theory for computing entropic cost of stretching BCP chains. We introduce a new variational method based on tessellations using medial set construction to compute space filling optimal chain packing within SSL and show that our approach results in a lower free energy chain packing relative to previous studies in SSL which included a constraint that chains within tubular domains have to stretch till 1D skeletal graphs. Critically, we show that reduced entropic cost of medial vs. skeletal packing qualitatively alters the equilibrium phase diagram based on the SSL, with DG only showing a stable composition window when stretching is not confined to 1D skeleton. Our medial model can also be extended to morphologies beyond networks and is easily adaptable to study packing frustration using simulation or experimental data thereby providing valuable insights to engineer molecular design to target yet unrealized novel self-assembled BCP morphologies. |
Tuesday, March 16, 2021 1:06PM - 1:18PM Live |
F63.00009: Exploring the Rich Phase Space of Asymmetric Copolymer Blends Aaron Lindsay, Andreas J. Mueller, Austin J. Peterson, Mahesh Mahanthappa, Timothy Lodge, Frank Bates Recently, we showed that blending two polystyrene-b-poly(1,4-butadiene) (SB) diblock copolymers can facilitate access to a dodecagonal quasicrystal (QC) as well as Frank-Kasper (FK) σ and A15 phases with massive unit cells (a ≈ 100 nm). Notably, this strategy marked a departure from past work, which, by and large, required both a high degree of architectural asymmetry and low molecular weight to drive similar phase behavior. However, in our past study we only examined the narrow case of a constant length corona block and a variable length core block, leaving unknown the limits of this strategy. In this work, we explore these limits via investigation of a series of SB blends judiciously designed to span the realm of possibilities encountered on blending two SB copolymers. We find using small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) that, although a high core block asymmetry yields the largest FK phase stability windows, even a modest increase in the molecular weight distribution, analogous to an increase in the overall dispersity, is sufficient to drive the emergence of these complex packings. |
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