Symmetry breaking in particle-forming diblock polymer/homopolymer blends
Symmetry breaking in particle-forming diblock polymer/homopolymer blends
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DOI：
10.1073/pnas.2006079117
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发表时间：
2020-07-21
影响因子：
11.1
通讯作者：
Dorfman, Kevin D.
中科院分区：
文献类型：
--
作者：
Cheong, Guo Kang;Bates, Frank S.;Dorfman, Kevin D.
组成不对称的二嵌段共聚物为理解软物质中四边形紧密堆积的弗兰克-卡斯珀相的出现提供了一个有吸引力的平台。在均匀密度的填充空间约束下，嵌段聚合物的相行为是由链拉伸和界面张力之间的直接竞争决定的。实验表明，在纯熔体状态下，由于构象不对称性不足而无法形成Frank-Kasper相的二嵌段共聚物在加入少量嵌段均聚物后，会从体心立方（bcc）紧密堆积胶束转变为一系列Frank-Kasper相（sigma到C14到C15），同时在湿刷状态下，还会出现从bcc到六边形堆积圆柱体的预期转变。本文给出的自洽场论数据定性地再现了实验相行为的显著特征。对均聚物分配的逐粒子分析为理解从高对称性的bcc相到低对称性的Frank-Kasper相的对称性破缺提供了基础，其中系统重新配置为体积不对称性增加的多面体延迟了宏观相分离的开始。
Compositionally asymmetric diblock copolymers provide an attractive platform for understanding the emergence of tetragonally close-packed, Frank-Kasper phases in soft matter. Blockpolymer phase behavior is governed by a straightforward competition between chain stretching and interfacial tension under the constraint of filling space at uniform density. Experiments have revealed that diblock copolymers with insufficient conformational asymmetry to form Frank-Kasper phases in the neat-melt state undergo an interconversion from body-centered cubic (bcc) close-packed micelles to a succession of Frank-Kasper phases (sigma to C14 to C15) upon the addition of minority-block homopolymer in the dry-brush regime, accompanied by the expected transition from bcc to hexagonally packed cylinders in the wet-brush regime. Self-consistent field theory data presented here qualitatively reproduce the salient features of the experimental phase behavior. A particle-by-particle analysis of homopolymer partitioning furnishes a basis for understanding the symmetry breaking from the high-symmetry bcc phase to the lower-symmetry Frank-Kasper phases, wherein the reconfiguration of the system into polyhedra of increasing volume asymmetry delays the onset of macroscopic phase separation.