Cheong Guo Kang, Bates Frank S, Dorfman Kevin D
Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455.
Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455
Proc Natl Acad Sci U S A. 2020 Jul 21;117(29):16764-16769. doi: 10.1073/pnas.2006079117. Epub 2020 Jul 7.
Compositionally asymmetric diblock copolymers provide an attractive platform for understanding the emergence of tetragonally close-packed, Frank-Kasper phases in soft matter. Block-polymer 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 (σ 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.
组成不对称的二嵌段共聚物为理解软物质中四方密堆积的弗兰克 - 卡斯帕相的出现提供了一个有吸引力的平台。在以均匀密度填充空间的约束下，嵌段聚合物的相行为受链拉伸和界面张力之间直接竞争的支配。实验表明，在纯熔体状态下构象不对称性不足以形成弗兰克 - 卡斯帕相的二嵌段共聚物，在干刷状态下加入少量嵌段均聚物后，会经历从体心立方（bcc）密堆积胶束到一系列弗兰克 - 卡斯帕相（σ相到C14相再到C15相）的相互转变，同时在湿刷状态下会伴随着从bcc相到六方堆积圆柱体的预期转变。本文给出的自洽场理论数据定性地再现了实验相行为的显著特征。对均聚物分配的逐个粒子分析为理解从高对称的bcc相到低对称的弗兰克 - 卡斯帕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。
