Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session F17: Self-Assembled SystemsFocus Recordings Available
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Sponsoring Units: DPOLY Chair: Dan Ye, Dow Room: McCormick Place W-184BC |
Tuesday, March 15, 2022 8:00AM - 8:36AM |
F17.00001: DPOLY Invited Talk
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Tuesday, March 15, 2022 8:36AM - 8:48AM |
F17.00002: Theory of Microphase Separation in Concentrated Solutions of Sequence Specific Charged Heteropolymers Siao-Fong Li, Murugappan Muthukumar The chemical sequences of heteropolymers play a major role in controlling self-assembly and |
Tuesday, March 15, 2022 8:48AM - 9:00AM |
F17.00003: Is the "Bricks-and-Mortar" Mesophase Bicontinuous?: Dynamic Simulations of Miktoarm Block Copolymer/Homopolymer Blends Cody T Bezik, Joshua A Mysona, Ludwig Schneider, Abelardo Ramirez-Hernandez, Marcus Mueller, Juan De Pablo A mesophase in binary blends of A-b-(BA')3 miktoarm star block copolymers and A homopolymers has been reported to consist of aperiodic discrete domains of A embedded in a continuous matrix of B, up to very high concentrations of A. Because of the material's potential as a thermoplastic elastomer, an understanding of its structural and mechanical properties, including its domain connectivity, rheological behavior, response to shear and to uniaxial tension, is warranted. These properties are explored here using dissipative particle dynamics in three dimensions. These simulations establish that the "bricks-and-mortar" phase while appearing discrete in two dimensions is bicontinuous. The simulations focusing on dynamics establish that the role of molecular bridging dominates the mechanical behavior, outweighing the influence of microphase segregation even at the highest homopolymer concentrations we study. Additionally, the phase is sensitive to the application of high shear, leading to anisotropic mechanical responses, which has ramifications for processability. We find that upon application of shear the phase becomes closer to its speculated discrete nature. Molecular simulations on our longest accessible timescales show that the material is unable to relax back to its original structure, suggesting that the morphology depends heavily on the processing pathway. |
Tuesday, March 15, 2022 9:00AM - 9:12AM |
F17.00004: Phase separation and anomalous domain growth in binary blends of polymer-grafted nanoparticles Michael R Bockstaller, Yue Zhai, Wenjie Wu, Alamgir Karim Surface modification of nanoparticles with polymer ligands has emerged as an important strategy to control interactions and assembly in colloidal systems. Recent research has revealed that the tethering of polymeric ligands to the surface of nanoparticles (so called ‘particle brush’) can induce the autonomous organization of multicomponent particle brush mixtures into monotype domain structures in a process that bears similarity to phase separation in binary polymer blends. |
Tuesday, March 15, 2022 9:12AM - 9:24AM |
F17.00005: Altering block copolymer (BCP) self-assembly and phase behavior with low-intensity magnetic fields Grace V Kresge, Karthika Suresh, Michelle A Calabrese While block copolymers (BCPs) are promising materials due to their tunable structure and functionality, practical methods for processing BCPs into materials with long-range order remain challenging. We recently discovered magnetic field-induced phase formation in weakly diamagnetic, coil-coil BCPs that cannot be explained by traditional mechanisms of domain alignment. Here, stable ordered phases rapidly form after applying weak magnetic fields to low viscosity solutions of geometrically-isotropic BCP micelles. Magnetorheology confirms that phase formation is accompanied by an increase in modulus of up to six orders of magnitude; phases are stable for hours to days upon field removal. Small angle x-ray scattering indicates that the induced phase depends on BCP characteristics and magnetization time. With increasing magnetization time, structure formation appears to follow multi-step trajectory across the temperature vs. concentration phase diagram, where B-field causes effects similar to increasing T or φp. Fully understanding this anomalous assembly phenomenon will afford access to BCP structures and associated lengthscales inaccessible via traditional routes, and provide a platform for developing well-ordered BCP materials under mild processing conditions. |
Tuesday, March 15, 2022 9:24AM - 9:36AM |
F17.00006: 3D Imaging and Analysis of the Nanomorphology of Polymer Films to Reveal Synthesis, Structure and Property Relationships Falon C Kalutantirige, Hyosung An, Qian Chen Polyamide (PA) membranes synthesized via interfacial polymerization of acyl chloride and amine monomers develop heterogeneous crumpled morphologies. Although PA thin-film composite membranes are widely used in the water desalination industry, there is very little understanding of the relationship between this crumpled structure and the performance properties of the membranes, primarily due to the irregularity of these soft nanomorphologies. With the use low-dose electron tomography, followed by 3D reconstruction and morphometry, we strive to overcome the challenge of quantifying the crumpled nanomorphology of PA membranes, thereby uncovering relationships between synthesis, morphology, solvent permeability and mechanical properties. We probed the change in morphology of PA membranes of nine different synthetic conditions by varying the monomer concentrations. Using different morphometric approaches to quantify the crumple morphology, including curvature mapping, machine-learning-based gaussian mixture model and graph theory-based skeletonization, we were able to show a Turing instability relationship between monomer concentration and crumple morphogenesis, along with a correlation between the crumple nanomorphology with methanol permeance and apparent modulus of the PA films. |
Tuesday, March 15, 2022 9:36AM - 9:48AM |
F17.00007: Self-assembly of semicrystalline bottlebrush statistical copolymers with various grafting density Mingqiu Hu, Hong-Gyu Seong, Todd S Emrick, Javid Rzayev, Thomas P Russell We synthesized bottlebrush statistical copolymers with poly(ethylene oxide) (PEO) and poly(dimethylsiloxane) (PDMS) side chains grafted to a polynorbornene backbone. The grafting density was tuned through copolymerization with a phenyl derivative of norbornene. An analysis of the one-dimensional scattering length density correlation function revealed that the backbone acted as a transition zone between the PEO and PDMS domains at high grafting density, while forming a distinct third domain with a smaller density than both PEO and PDMS at low grafting density. Self-consistent field theory calculations showed that zigzagging of the backbone, driven by the microphase-separation of PEO and PDMS, was essential for the formation of a distinct backbone domain at low grafting densities. The PEO crystallites were randomly oriented within the amorphous PEO domains. Ordering PEO chains into crystal unit cells inevitably disrupted the nematic order of PEO side chains in the melt and the lateral ordering of the microphase-separated lamellar morphologies. As a result, both the static intrinsic birefringence and form birefringence decreased when PEO crystallized upon cooling. |
Tuesday, March 15, 2022 9:48AM - 10:00AM |
F17.00008: Effects of Skewness on the Formation of Complex Spherical Phases in Disperse Diblock Copolymers Chi Lai, Anchang Shi One of the most captivating features of block copolymers is their ability to self-assemble into a plethora of ordered structures. In the simplest case of monodisperse linear diblock copolymers, the phase behavior is governed by the strength of the interactions between the two chemically distinct blocks and their molecular weights. For disperse systems, the self-assembly can also be influenced by the molecular weight distribution (MWD). The most widely used quantity to characterize the MWD is the dispersity index that characterize the width of the MWD. However, recent experiments have begun to reveal the importance of skewness of the MWD in the self-assembly process. Therefore, the MWD shape matters, such that different self-assembled structures could be observed in samples with similar dispersity index and different skewness. In our study, we examine the effect of skewness on the formation of the complex spherical packing phases in disperse diblock copolymers using the self-consistent field theory. We find that the MWD skewness is a key parameter regulating the selection of accessible spherical packing phases, demonstrating the importance of the MWD shape. |
Tuesday, March 15, 2022 10:00AM - 10:12AM |
F17.00009: Side Chain Induced Morphology Changes in Brush-Linear Diblock Copolymers Jaemin Park, Sheng Li Brush-linear block copolymers represent an interesting class of materials as they exhibit complex phase morphology with characteristics of both coil-coil and rod-coil block copolymers. In this study, we investigate the self-assembly of brush-linear block copolymers where both the brush side chain density and chain length are systematically varied. A poly(pentafluorophenyl acrylate-b-styrene) (PPFPA-b-PS) linear diblock copolymer is first prepared as the precursor polymer. The PPFPA block is then reacted with amine-functionalized poly(ethylene glycol) (PEG) to create brush-linear type block copolymers of the chain structure (PPFPA-g-PEG)-b-PS. Different degrees of PEG substitution are conducted, and the resulting brush-linear block copolymers are examined to determine their bulk morphologies by small-angle X-ray scattering (SAXS). As the degree of PEG side-chain substitution increases, block copolymer morphology is found to transition from lamellae to a newly formed frustrated lamellae then to hexagonally-packed cylinder. Furthermore, when PEG chains of longer chain length are used, the same morphology transition is again observed while these transitions occur at even lower degrees of side-chain substitution. |
Tuesday, March 15, 2022 10:12AM - 10:24AM |
F17.00010: Formation of complex spherical packing phases in binary blends of diblock copolymers Yu Li The emergence and relative stability of complex spherical packing phases in binary blends composed of A1B1 and A2B2 diblock copolymers are systematically studied using the polymeric self-consistent field theory. Phase diagrams are constructed in a large parameter space of the system. The results demonstrated that complex spherical packing phases including the Frank-Kasper A15 and s phases, and the Laves C14 and C15 phases can be stabilized by the addition of longer A2B2 copolymers to asymmetric A1B1 - copolymers. Furthermore, the formation of complex spherical packing phases requires that the added A2B2 - copolymers have a longer A-block. A detailed analysis of the block distributions reveals the existence of inter-and intra-domain segregation of different copolymers, which provides a mechanism to aid the formation of spherical domains with different sizes and shapes. The predicted phase behaviours require that the added A2B2 - copolymers have a longer A-block and an overall chain length at least comparable to the host copolymer chains. Our results are in good agreement with available experimental and theoretical results. The study demonstrated that binary blends of diblock copolymers provide an efficient route to regulate the emergence and stability of complex spherical packing phases. |
Tuesday, March 15, 2022 10:24AM - 10:36AM |
F17.00011: Equilibrium Nature of Self-Assembled Polymer-Grafted Nanoparticles in a Homopolymer Matrix Clement Koh, Sanat K Kumar, Gary S Grest It is commonly believed that in systems of polymer grafted nanoparticles (NPs) in homopolymer matrices, the transition between various NP morphologies, for instance well-dispersed NPs to phase separated NPs, occur spontaneously. To explore this assumption, we conducted large-scale molecular dynamics simulations of grafted NPs in a chemically identical polymer melt. The model is a simple bead sping model with standard Lennard-Jones interactions that were previously proven successful in modeling the self-assembly observed in experiments. By varying the tunable parameters of grafting density, matrix polymer chain length and grafted polymer chain length, we were able to extensively probe the morphology space and arrive at several key findings. Firstly, not only is there a gradual transition between the different self-assembled NP states, regardless of initial configuration states (well-dispersed or aggregated), one seems to be able to arrive at the same final morphology eventually, especially for short length-scale conformations. These results appear to validate the equilibrium nature of these morphologies. Second, we find that while the surfactancy of the NPs drives self-assembly of the diverse array of morphologies observed experimentally, the tuning of NP size is crucial to access the phase-separated morphology. |
Tuesday, March 15, 2022 10:36AM - 10:48AM |
F17.00012: Stabilizing Binary Mesocrystals via Block Copolymer Blends Jiayu Xie, Chi Lai, Anchang Shi Previous work has demonstrated that multiblock block copolymers with designed architectures offer unlimited opportunities to obtain novel nanoscale structures. However, synthesizing multiblock copolymers with complex architectures is challenging and expensive. In this research we explore the possibility of using blends of simple copolymers with designed secondary interactions as an alternative route to access desired structures. Specifically, we examined the phase behavior of ABC/DB/EB ternary blends and AB/CD binary blends using the self-consistent field theory, aiming to stabilize the desired binary mesocrystals composed of two types of spherical domains. Conditions for forming various binary mesocrystals are obtained from the resulting phase diagrams. We also discuss the mechanisms to form these novel phases in both cases. Our study offers a simpler approach to access the novel macromolecular binary mesocrystals and adds to the understanding of the self-assembling behaviour of block copolymer blends. |
Tuesday, March 15, 2022 10:48AM - 11:00AM |
F17.00013: Entropic Mixing of Ring/Linear Polymer Blends Gary S Grest, Steven J Plimpton, Ting Ge, Thomas C O'Connor The closed-loop structure of ring polymers enables them to be threaded by linear polymers. This results in an entropic mixing (negative χ) compared to linear/linear and ring/ring blends. Results from molecular dynamics (MD) simulations for bead-spring chains of length 50 - 400 for linear/linear, ring/ring and ring/linear blends will be presented. These chains are long enough that the rings are threaded by multiple linear chains. The phase boundary for the linear/linear and ring/ring blends is determined by MD simulations, supplemented with a Monte Carlo chain exchange process. In analogy with SANS data, we measured the static structure function S(q) in which the scattering lengths bi = ± 1 for the two components and fit the resulting data to the random phase approximation (RPA) to determine χ. In the limit that the two components are equal, χ = 0 for the linear/linear and ring/ring blends, while χ < 0 for the ring/linear blends. As the incompatibility of the two components increases, the number of linear chains threading each ring decreases, and χ increases but remains less than for the linear/linear and ring/ring blends. Eventually, the linear chains de-thread the ring polymers and the ring/linear blends phase separate into two macroscopic phases. |
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