Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session J33: Thermodynamics and Structures of Microstructured PolymersFocus
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Sponsoring Units: DPOLY Chair: Sangwoo Lee, Rensselaer Polytechnic Institute Room: 505 |
Tuesday, March 3, 2020 2:30PM - 3:06PM |
J33.00001: BREAK
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Tuesday, March 3, 2020 3:06PM - 3:18PM |
J33.00002: Packing Frustration in Block Copolymer Double Gyroids: Is it really all about the tubular domains? Abhiram Reddy, Xueyan Feng, Edwin Thomas, Gregory Grason Understanding the molecular-scale mechanisms that lead to self-assembly of complex 3D morphologies remains an active area of research in soft matter systems. Block copolymers (BCPs) provide an exciting avenue to probe these mechanisms due to advancements in theory, synthesis and characterization tools. In this talk, we will revisit the thermodynamic connection between stability of triply-periodic network (TPN) phases, such as the Double Gyroid (DG), and packing frustration, or the variation in chain extension required by space filling constraint. We propose Medial Thickness (MT) analysis which provides a generic and practical measure of domain thickness of BCP morphologies of any arbitrary topology. Based on MT analysis of both theoretical models and experimental measurements of inter-block dividing surfaces of DG, we argue that previous measures of domain thickness severely overestimate both magnitude and dispersity of chain extension required to fill the tubular domains of TPN, belying the heuristic picture that their dominant thermodynamic costs arise from the stretching to reach the center of tubular interconnects. These insights also lead us to revisit longstanding question about absence of DG in the equilibrium phase diagram of strongly-segregated BCPs. |
Tuesday, March 3, 2020 3:18PM - 3:30PM |
J33.00003: Effects of Tacticity on the Formation of Bicontinuous Phases in Diblock Copolymers Chi To Lai, An-Chang Shi The most prominent feature of block copolymers is their ability to self-assemble into ordered structures with periods typically on the scale of 10-100 nm. The symmetry of these ordered structures can depend on a number of factors, including block composition, strength of interactions, conformational asymmetry and tacticity. Tacticity is defined as the order of neighboring dangling groups along a polymer backbone, and influences many properties, ranging from thermal to rheological to conformational. In particular, block copolymers of the same composition with different tacticities could form different microphases. Recent experiments on stereoregular diblock copolymers have also observed the existence of the bicontinuous double-diamond phase, which is not found in neat atactic diblock copolymers. On the other hand, the effects of tacticity on self-assembly is yet to be completely understood. We develop a toy model to incorporate the effects of tacticity within the theoretical framework of self-consistent field theory. We then examine how the formation of bicontinuous phases in diblock copolymers is affected by the inclusion of tacticity effects. |
Tuesday, March 3, 2020 3:30PM - 3:42PM |
J33.00004: Cylindrical to Lamellar Microdomain Order to Order Transition upon Heating for Upper Critical Ordering Transition Block Copolymer Seonghyeon Ahn, Yeseong Seo, Chao Duan, Lixun Zhang, Wei-hua Li, JinKon Kim For block copolymers with upper critical ordering transition (UCOT) where χ decreases with increasing temperature, the sequence of order to order transition (OOT) upon heating of AB diblock and A1BA2 triblock copolymers with UCOT is as follows: lamellae to gyroids to cylinders to spheres before order to disorder transition. However, the opposite direction OOT is impossible in UCOT block copolymers. |
Tuesday, March 3, 2020 3:42PM - 3:54PM |
J33.00005: Unique self-assembly behaviors of ABCA tetrablock copolymer Qiong Xie, Wei-hua Li The self-assembly behavior of linear ABCA tetrablock copolymers is investigated using self-consistent field theory (SCFT). Although the general mechanism of block copolymer self-assembly has been well established, the self-assembly behaviors of some block copolymers are still hard to be understood and are even quite counterintuitive. Here we focus on the self-assembly of symmetric ABCA linear tetrablock copolymer. Our results indicate that the Janus-like superspherical phase can exist stably when the Flory-Huggins interaction between B and C blocks is much larger than the other two interactions. Moreover, a helical-Janus spherical phase is predicted to compete with the Janus phase. Meanwhile, the Janus-like supercylinder is predicted to be only metastable, and instead supercylinders composed of B/C-helices and B/C-stacked-disks are predicted to be stable. The stability of these novel structures is mainly dictated by the competition between the stretching energy and interfacial energy. |
Tuesday, March 3, 2020 3:54PM - 4:06PM |
J33.00006: Tuning Helical Structures via Designed Block Copolymer Systems Mei-jiao Liu, Wei-hua Li Block copolymers confined in nanopores provide unique achiral systems for the formation of helical structures. With AB diblock copolymers, stable single and double helical structures are observed. Aiming to obtain more different helical structures, we replace AB diblock copolymer with linear ABC triblock copolymers. We speculate that a core-shell superstructure is formed within the nanopore, which is composed of a C-core cylinder wrapped by B-helices within the A-shell. A number of helical structures with strands ranging from 1 to 5 are predicted by self-consistent field theory (SCFT), and in general, the number of strands decreases as the volume fraction of C-block fC increases in a given nanopore. More surprisingly, the variation of helical strand in the confined system is in an opposite trend to that in the bulk, which is mainly resulted by the constraint of the cylindrical confinement on the change of the curvature between the outer A-layer and the inner B/C-superdomain. Furthermore, adding C homopolymers to ABC triblock copolymers, the helical structures with more strands are predicted. Our work demonstrates a facile way to fabricate different helical superstructures. |
Tuesday, March 3, 2020 4:06PM - 4:18PM |
J33.00007: Miscibility Enhancement in Polyisoprene-Polyolefin Block Copolymers via Styrene Incorporation Sravya Jangareddy, Richard Register Polydienes like polyisoprene (PI) and polyolefins like hydrogenated mid-vinyl polybutadiene (hPB) generally show limited compatibility (high interaction energy density, X). Both the regular mixing model and the copolymer equation suggest that styrene units (S) should boost inter-block miscibility when incorporated in small amounts into hPB, up to 40 wt% S, via random copolymerization. Mixing thermodynamics in symmetric polydiene-polyolefin block-random copolymers composed of PI and a selectively saturated random copolymer of mid-vinyl polybutadiene and styrene (hSBR) were investigated via location of the order-disorder transition (ODT) temperatures. Block and “block-random” copolymers were prepared by anionic polymerization, followed by selective saturation of the butadiene units. ODT measurements show that X is 0.74 MPa at 0 wt% S, and exhibits the predicted parabolic variation with wt% S, with a minimum in X near 40 wt% S. Near the minimum, one-phase and two-phase blends of an hSBR with PIs of two different molecular weights, revealed that 0.10 < X < 0.16 MPa, indicating that the copolymer equation provides a better description of the mixing thermodynamics than the regular mixing model (for which X = 0 at the minimum). |
Tuesday, March 3, 2020 4:18PM - 4:30PM |
J33.00008: WITHDRAWN ABSTRACT
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Tuesday, March 3, 2020 4:30PM - 4:42PM |
J33.00009: Pattern Imprinted Polyacrylonitrile Thin Films Using an Ionic Liquid Chuqing Yuan, Rebecca Barry, Kathryn Beers, Alamgir Karim Polyacrylonitrile (PAN)-based conductive graphitic microstructures have tremendous potential for a variety of applications such as patterned electrodes, and anisotropic conductive films in the electronics industry due to its high carbonization yield. However, because of the crystallinity and high melting point of pristine PAN, thin films are difficult to get patterned at routine temperatures and pressures via methods such as capillary force lithography (CFL), a straightforward lithographic technique. We demonstrate that adding ionic liquid (IL) can greatly improve the imprintability of PAN by decelerating the crystallization rate and providing the needed mobility at accessible temperatures for efficient mold filling. The effect of IL additives concentration, annealing temperature and hold time of patterned PDMS elastomer on the imprintability of PAN are well-correlated in a balancing act. The resulting patterned films demonstrate extraordinary IL removal ability at the end of the process, and thermal stability of final patterned structures, promising results on easy patterning route to create graphitic structures after carbonization for multitude of applications ranging from sensors to membranes. |
Tuesday, March 3, 2020 4:42PM - 4:54PM |
J33.00010: Glass Transitions in PS-TiO2 Nanocomposites Mircea Chipara, Elvia Curiel Izaguirre, Dorina Chipara, Mataz Alcoutlabi Atactic polystyrene is considered a fully amorphous polymer. Homogeneous solutions of atactic polystyrene in chloroform were obtained by adding the two components and stirring the mixture for 4 hours. After homogenization, the polystyrene-chloroform solutions were moved in a larger beaker and sonicated for about 1 hour. Then, deionized water was suddenly added to the polymer solution, without interrupting the sonication process. The added volume of water was typical twice the volume of the polymer solution. The sonication was stopped after 15 minutes and the polymer was collected and then dried in an oven at 90 oC, for about 12 h. Full water evaporation was confirmed by TGA. Nanocomposites of PS-TiO2, containing various amounts of TiO2, have been obtained by using this procedure. It was expected that the rapid collapse of the polymeric chain (as the nonsolvent was added) would trap the nanofiller within the polymeric matrix. |
Tuesday, March 3, 2020 4:54PM - 5:30PM |
J33.00011: The pliable morphology of block copolymer crystals Invited Speaker: Edwin Thomas Block copolymers form soft crystals of ‘mesoatomic’ building blocks comprised of many thousands of molecules, whose sub-unit-cell configurations couple strongly to sub- and super-strate boundary conditions and symmetries. High-fidelity 3D tomographic structural information from both the near-surface as well as interior regions is key to understanding the properties of a given polymer structure. BCPs having a tubular network morphology are particularly attractive for applications ranging from photonic crystals to 3D batteries. Additionally, such complex 3D structures are quite sensitive to confinement by interfaces. We study the 3D domain morphology of a solution-cast block copolymer double gyroid. Analysis reveals that the morphology reconstructs in the near surface regions as well as with non-affine deformation of the sub-unit-cell symmetry in the interior region. Such strongly pliable morphological behavior has strong implications for properties, raising the question as to whether highly perfect cubic self assembled BCP structures are possible. |
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