Bulletin of the American Physical Society
APS March Meeting 2024
Monday–Friday, March 4–8, 2024; Minneapolis & Virtual
Session Z32: Polymer Structure, Morphology, and Self-Assembly |
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Sponsoring Units: DPOLY Chair: Joshua Lequieu, Drexel University Room: 102D |
Friday, March 8, 2024 11:30AM - 11:42AM |
Z32.00001: Liquid-like states in micelle forming diblock copolymer melts Kevin D Dorfman, Zhen-Gang Wang Compositionally asymmetric diblock copolymers form micelles that pack onto an ordered lattice when the system is cooled below the order-disorder transition (ODT). At temperatures slightly above the ODT, the fluid structure is inhomogeneous and consists of fluctuating micelles. We have developed a mean-field picture of this fluctuating micelle state by seeding self-consistent field theory calculations with initial conditions generated from molecular dynamics simulations of the Kob–Anderson fluid. These calculations reveal a large number of disordered liquid-like states that are nearly degenerate with the equilibrium body-centered cubic (bcc) structure that would emerge in the ordered state. Moreover, the typical micellar spacings in the disordered liquid are slightly swollen compared to bcc. The presence of many local minima suggests the existence of a rugged free energy landscape within the disordered micelle state, which may be the origin of the anomalously slow ordering kinetics of micelle-forming systems. |
Friday, March 8, 2024 11:42AM - 11:54AM |
Z32.00002: Network Phase with Frank-Kasper-Like Symmetry from Controlled Self-Assembly of High-χ Star-Block Copolymers Cheng-Yen Chang, Gkreti-Maria Manesi, Apostolos Avgeropoulos, Wei-En Wang, Yu-Chueh Hung, Rong-Ming Ho Network phases can be obtained by using PS-selective solvent for controlled self-assembly of high-χ lamellae-forming polystyrene-block-polydimethylsiloxane (PS-b-PDMS) block copolymers. By taking advantage of the topology effect on BCP self-assembly, network phases with higher packing frustration can be obtained. With the combined effect of high χ and molecular topology, apart from double gyroid (trigonal planar structure) and double diamond (tetrahedral structure or tetrapod), a unique network phase with double networks of PDMS in PS matrix but mixed trigonal and crossing structure can be found as evidenced in reconstruction images by electron tomography. Most interestingly, the small angle X-ray scattering result give the profile same as the A15 phase, one of Frank-Kasper phases, with space group of Pm3n. The observed phase behaviors might provide the conceptual ideas for the development of network phase from FK phase via space filling to decipher the origins of the complex network phases due to the character of malleable mesoatoms (i.e., microphase-separated domains) that gives the adaptation with complex curvatures. |
Friday, March 8, 2024 11:54AM - 12:06PM |
Z32.00003: Microphase Separation of Particle-Forming AB/AC Diblock Copolymer Blends with Immiscible Core Blocks Zachary Gdowski, Samuel Swartzendruber, Mahesh Mahanthappa, Frank S Bates The structural behavior of particle-forming binary blends of AB and AC diblock copolymer blends with common A block coronae and nearly immiscible core segments (B and C) is relatively unexplored. Such micelle blends are expected to either macrophase separate into AB-and AC-rich morphologies or to co-assemble into a single microphase-separated morphology, depending on the relative particle sizes of the individual diblocks. We synthesized asymmetric diblocks with poly(ethylene-alt-propylene) corona blocks and either poly(ethylene oxide) or poly(dimethylsiloxane) core segments and studied their blend morphologies using small-angle X-ray scattering (SAXS). When the two diblock particle sizes are well-matched, the blends assemble into single-phase BCC morphologies akin to intermetallic solid solutions. In blends with mismatched particle sizes, we observe the formation of either liquid-like packings of micelles, BCC solid solutions, or gradual evolution into a tetrahedrally close-packed C14 Laves phase. These findings provide insights into the phase evolution and future design of complex micelle morphologies of AB/AC block copolymer alloys. |
Friday, March 8, 2024 12:06PM - 12:18PM |
Z32.00004: Coarse-grained models of bottlebrush polymers from solutions to melts using a wormlike cylinder model Haisu Kang, Charles E Sing Bottlebrush polymers are a class of macromolecules composed of densely grafted side chains on a linear polymer backbone. The crowding of side chains leads to steric repulsions, which give the polymer a stiff conformation with molecular thickness. Despite their great engineering potential, particle-based simulation of these materials is challenging due to the large number of monomers needed to describe each molecule. We recently demonstrated that it is possible to describe a bottlebrush as a linear semi-flexible chain based on the wormlike cylinder (WLCy) model, which does not include explicit side chains. These implicit side chain (ISC) models drastically decrease the computational cost by directly mapping to simulations of the conformation of individual bottlebrushes. However, the ISC model is limited to dilute solution, which is far from real functional materials in application in bulk melts or concentrated solutions. |
Friday, March 8, 2024 12:18PM - 12:30PM |
Z32.00005: Stable and Unstable Tiling Patterns Formed by ABC Miktoarm Star Triblock Terpolymers of Symmetric Interactions Qiang Wang, Cody Hawthorne, Juntong He Several discrepancies exist among previous self-consistent field calculations of symmetrically interacting ABC miktoarm star triblock terpolymers, in part due to the differences in their candidate phases and the possible numerical inaccuracies. Here we address this issue by including all known tiling patterns, as well as several lamellar-type phases known to bound the regions in the parameter space occupied by these patterns. After carefully studying the effect of numerical parameters on the free-energy accuracy, the central region of the phase diagram is constructed in detail; both the (3.4.6.4) pattern and the 3D phase of hierarchical-hexagonal lamellae are found to be stable for the first time. The energetic and entropic contributions to the free-energy density of several phases are analyzed and compared in detail to reveal their stability mechanisms, including the important (32.4.3.4) pattern. Comparisons to previous studies of the same model system are present throughout, with our results resolving the aforementioned discrepancies and providing a sound basis for future work to build upon. |
Friday, March 8, 2024 12:30PM - 12:42PM |
Z32.00006: Influence of the hydrophilic corona block on drug encapsulation during polymerization induced self-assembly Guanrui Li, Ralm G Ricarte Block copolymer nanoparticles (PNPs) are effective for delivering hydrophobic drugs within the body due to their versatility in functionality and morphology. Recently, polymerization induced self-assembly (PISA) has emerged as an efficient and facile method for synthesizing PNPs. During PISA, polymerization, self-assembly, and drug encapsulation occur simultaneously. This simplified protocol achieves high PNP concentrations while avoiding the use of toxic organic solvents. However, the mechanism of drug encapsulation during PISA remains an open question. Previously, we found that the targeted drug concentration governed both the PNP morphology and drug encapsulation efficiency. In contrast, the hydrophobic core block molar mass affected the morphology, but had minimal influence on encapsulation efficiency. Here, we investigate how the hydrophilic corona affects drug encapsulation in PISA PNPs. The model block copolymer is poly(ethylene glycol) methyl ether-block-poly(2-hydroxypropyl methacrylate), while the model drug is phenylacetic acid. PNP morphology is characterized using transmission electron microscopy, small angle X-ray scattering, and dynamic light scattering. Drug encapsulation efficiency is quantified through 1H nuclear magnetic resonance diffusion-ordered spectroscopy. Through systematic determinations of morphology and encapsulation efficiency, we derive a stronger understanding of the relationship between PNP structure and sequestration during PISA. |
Friday, March 8, 2024 12:42PM - 12:54PM |
Z32.00007: Two-Regime Conformation of Grafted Polymer on Nanoparticle Determines Symmetry of Nanoparticle Self-assembly Ji Woong Yu, Hongseok Yun, Won Bo Lee, YongJoo Kim One of the key design factors that regulate the properties of grafted nanoparticles (GNPs) and their self-assembly is the conformation of the grafted polymer. On the curved surface of the GNP core, the conformation of the polymer chain is not uniform in the radial direction. The segment is a non-gaussian chain in the concentrated polymer brush (CPB) regime near the interface between GNP core and grafted polymer, while it is less constrained in the semi-dilute polymer brush (SDPB) regime near the surface of GNP. In this talk, the property of polymer conformation showing crossover behavior at the CPB/SDPB threshold through the coarse-grain molecular dynamics simulation of nanoparticles with explicit grafted chains will be discussed. Moreover, the self-assembly structure depends on the effective softness which is defined as a function of the threshold of two regimes estimated from the conformation of the polymer. |
Friday, March 8, 2024 12:54PM - 1:06PM |
Z32.00008: Structure and composition effects on the magnetically-induced ordering of poloxamer solutions Grace Kresge, Arit Das, Christopher A Neal, Milena Mesfun, Michelle A Calabrese Directing the self assembly of diamagnetic block copolymers (BCPs) via magnetic fields can induce a rich variety of physical phenomena, including the formation and enhancement of various morphologies. Previous work has shown that amphiphilic poloxamer micelle solutions exposed to low intensity magnetic fields (B ≥ 0.05 T) demonstrate a disorder-to-order transition driven by magnetically-induced change in polymer-solvent parameters. This study shows magnetically-induced structure formation across 11 poloxamers of varying molecular weight and block composition. Notably, the critical magnetization time prior to ordering, denoted as tcrit, correlates strongly to variables associated with the thermodynamics of micellization, such as hydrophobic block size. Remarkably, all 11 samples show an enhancement in modulus when processed magnetically vs thermally, with enhancement factor (Gmag/GT) showing a strong molecular weight dependence. This increase in enhancement factor is explained in part by the slower transition kinetics of associated with lower molecular weight poloxamers, which was quantified via the Avrami model. Further insights into the role of poloxamer composition on the induced structure and ordering mechanism are discussed. This innovative approach to BCP processing enables discovery of structures and d-spacings inaccessible via traditional thermal processing routes, providing a platform for developing materials with precisely-controlled features at mild conditions. |
Friday, March 8, 2024 1:06PM - 1:18PM |
Z32.00009: Catalan and Half-Catalan numbers in Hyperbranched Polymers Pratyush Dayal, Neeldhara Misra, Surbhi Khewle
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Friday, March 8, 2024 1:18PM - 1:30PM |
Z32.00010: Effect of Solvent Uptake on Morphology in TAPB-PDA COFs Frederick L Beyer, David McLeod, Emil Sandoz-Rosado, Eric D Wetzel In the bulk, covalent organic frameworks (COFs) are able to form morphologies in which the individual two-dimensional molecules stack into crystallites reminiscent of tactoids in layered silicate clay minerals. Imine-linked, aromatic COFs formed from 1,3,5-tris(4-aminophenyl)benzene (TAPB) and terephthaldehyde (PDA) monomers have a molecular structure in which the TAPB nodes and PDA linkers form planar structures with a regular array of hexagonally-shaped openings. When stacked in an “eclipsed” arrangement, the hexagonal openings in the molecules create columnar pores oriented normal to the plane of the molecule. As such, bulk COFs have promise in applications like filtration, in which a liquid carrying a solute penetrates into the pores, allowing the solute to be selectively altered or bound. Because functionality would depend on morphology, it is important to understand the effect of solvent uptake on morphology. In this presentation, results will be presented for experiments in which small-angle X-ray scattering (SAXS) has been used to monitor morphology of bulk TAPB-PDA COFs in situ as a function of saturation with ethanol or water, and subsequent characterization to determine changes to morphology after the ethanol or water removal. |
Friday, March 8, 2024 1:30PM - 1:42PM |
Z32.00011: Parametrizing conjugated polymers as ribbon-like chains Srikant Sagireddy, Wesley Michaels, Jian Qin The performance of conjugated polymers (CPs) in flexible and lightweight electronics is directly correlated to their conformation and morphology. The chemistry of CPs endows them with anisotropic bending stiffness and twist stiffness, which cannot be fully captured by the standard worm-like chain (WLC) model. We recently developed the ribbon-like chain (RLC) model, which generalizes the WLC model and captures the conformational statistics of CPs. Here, we present a methodology to parametrize the RLC model using all-atom molecular dynamics (MD) simulations. The anisotropic bending stiffness and twist stiffness for a range of polymer chemistries are obtained by examining the orientation correlations of monomers along the chain backbone. These results allow for improved correlation between polymer chemistry and material properties, and serve as the basis for mesoscopic simulations of CPs. |
Friday, March 8, 2024 1:42PM - 1:54PM |
Z32.00012: Confinement of semi-crystalline bottlebrush random copolymers Xuchen Gan, Hong-Gyu Seong, Zhan Chen, Mingqiu Hu, Todd S Emrick, Thomas P Russell Bottlebrush copolymers incorporating distinct segments feature unique architectures and variable composition, affording unique opportunities to manipulate self-assembly and phase transitions. We synthesized a series of bottlebrush random copolymers (BRCP) with polystyrene (PS) and poly (ethylene oxide) (PEO) side chains. The bottlebrush architecture, where the side chains are anchored to backbone, inherently restrict the mobility of PEO. The relatively higher glass transition temperature of PS, compared to the crystallization temperature of PEO, places further confinement of PEO crystallization to the microdomain morphology established by the PS. The resultant limited mobility of PEO hinders its crystallization, ultimately leading to unusual microphase separation behavior and self-assembled structures. Confinements were adjusted by changing BRCP architectures as well as the annealing conditions to reveal the underlying mechanism. |
Friday, March 8, 2024 1:54PM - 2:06PM |
Z32.00013: Why Don't Some Strongly Attracting Heteropolymers Phase Separate? Jessica Jin, William M Jacobs A puzzling question in polymer science is why some heteropolymers that exhibit strongly attractive pairwise interactions do not undergo phase separation. Unlike simple liquids and colloidal suspensions, where the second virial coefficient can unambiguously predict whether phase separation occurs, this is not always the case for heteropolymer solutions. To investigate the sequence-dependent relationship between pairwise polymer interactions and phase behavior, we describe a simulation study of model heteropolymers that have identical second virial coefficients but divergent phase behaviors. By examining the potential of mean force and contact maps derived from the conformations of interacting polymer pairs, we are able to identify mechanistic factors responsible for their disparate phase behaviors. Our analysis establishes a computational tool for predicting heteropolymer phase behavior based solely on pairwise polymer interactions and their associated contact maps, and also advances our mechanistic understanding of the phase behavior of complex biopolymer systems. |
Friday, March 8, 2024 2:06PM - 2:18PM |
Z32.00014: Two-step Transition in 2D Melting of Hard-Core Soft-Shell Colloidal Particles Jihun Ahn, Su-Mi Hur, Abelardo Ramirez-Hernandez, So Youn Kim, Luis Adrian Padilla Salas, Seok Joon J Kwon In contrast to the 3D melting, where transitions primarily occur between solid and liquid phases, 2D melting is characterized by a two-step transition through an intermediate hexatic phase. Although the Kosterlitz–Thouless–Halperin–Nelson–Young (KTHNY) theory postulates two successive continuous transitions-from solid to hexatic, then to liquid--driven by the unbinding of topological defects, the precise 2D melting mechanism and the influence of the interaction potential between colloidal particles remain subjects of ongoing debate. This uncertainty is largely attributed to the extended interaction ranges characteristic of soft potentials, necessitating the study of extensive system sizes for a comprehensive understanding. In our study, we explore the melting scenario of a 2D Hard-Core Soft-Shell particle system. Using Molecular Dynamics simulations on a system encompassing over a million particles, we employed a range of analysis techniques, including Bond Orientation Order, Structure Factor, Entropy, and Positional Correlation to elucidate the melting process. Through our analysis of defect distribution, we pinpointed the expansive hexatic phase region observed in HCSS colloidal systems. |
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