Mueller Andreas J, Lindsay Aaron P, Jayaraman Ashish, Lodge Timothy P, Mahanthappa Mahesh K, Bates Frank S
ACS Macro Lett. 2020 Apr 21;9(4):576-582. doi: 10.1021/acsmacrolett.0c00124. Epub 2020 Mar 30.
The observation of complex, Frank-Kasper (FK) particle packings in diblock polymer melts has until recently been limited to low molecular weight, conformationally asymmetric polymers. We report temperature-dependent small-angle X-ray scattering (SAXS) studies of blends of a sphere-forming poly(styrene--1,4-butadiene) (SB) diblock polymer ( = 33.3 kg/mol, = / = 1.08, = 0.18) with two different poly(1,4-butadiene) (B) homopolymer additives. When the B additive is the same as that of the diblock core-forming B segment, these blends remarkably form tetrahedrally close-packed FK σ and Laves C14 and C15 phases with increasing B content. However, binary blends in which the B additive is 60% of that of the diblock B segment form only the canonical body-centered cubic (BCC) particle packing and hexagonally-packed cylinders (HEXc). The observed phase behavior is rationalized in terms of "wet" and "dry" brush blending, whereby higher B drives stronger localization of the homopolymer in the particle cores while preserving the interfacial area per SB diblock chain. The consequent packing constraints in these blends destabilize the BCC packing, and FK phases emerge as optimal minimal surface solutions to filling space at constant density while maximizing local particle sphericity.
直到最近，在双嵌段聚合物熔体中对复杂的弗兰克-卡斯帕（FK）粒子堆积的观察还仅限于低分子量、构象不对称的聚合物。我们报告了一种形成球体的聚（苯乙烯-1,4-丁二烯）（SB）双嵌段聚合物（ = 33.3 kg/mol， = / = 1.08， = 0.18）与两种不同的聚（1,4-丁二烯）（B）均聚物添加剂的共混物的温度依赖性小角X射线散射（SAXS）研究。当B添加剂与双嵌段核心形成B段的添加剂相同时，随着B含量的增加，这些共混物显著形成四面体密堆积的FK σ相以及Laves C14和C15相。然而，B添加剂为双嵌段B段的60%的二元共混物仅形成标准的体心立方（BCC）粒子堆积和六方堆积圆柱体（HEXc）。观察到的相行为根据“湿”和“干”刷状共混进行了合理化解释，即较高的B 促使均聚物在粒子核心中更强地定位，同时保持每个SB双嵌段链的界面面积。这些共混物中随之而来的堆积限制使BCC堆积不稳定，并且FK相作为在恒定密度下填充空间同时最大化局部粒子球形度的最佳最小表面解决方案而出现。
