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-block-1,4-butadiene) (SB) diblock polymer (M_n = 33.3 kg/mol, Đ = M_w/M_n = 1.08, f_B = 0.18) with two different poly(1,4-butadiene) (B) homopolymer additives. When the B additive M_n 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 M_n 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 M_n 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.

中文翻译：

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二嵌段聚合物/均聚物共混物中 C15 Laves 相的出现

直到最近，对二嵌段聚合物熔体中复杂的 Frank-Kasper (FK) 颗粒填料的观察仅限于低分子量、构象不对称的聚合物。我们报告了球状聚（苯乙烯嵌段-1,4-丁二烯）（SB）二嵌段聚合物（Mn = _33.3 kg/mol，Đ ）混合物的温度相关小角 X 射线散射 (SAXS) 研究= M _w / M _n = 1.08, f _B = 0.18) 与两种不同的聚 (1,4-丁二烯) (B) 均聚物添加剂。当 B 添加剂M _n与形成二嵌段核的 B 链段相同，随着 B 含量的增加，这些共混物显着形成四面体密排 FK σ 和 Laves C14 和 C15 相。然而，其中 B 添加剂M _n是二嵌段 B 链段 60% 的二元混合物仅形成规范的体心立方 (BCC) 颗粒堆积和六角堆积圆柱体 (HEXc)。观察到的相行为在“湿”和“干”刷混合方面是合理的，因此更高的 B M _n在保持每个 SB 二嵌段链的界面面积的同时，驱动均聚物在颗粒核心中更强的定位。这些混合物中随之而来的堆积约束使 BCC 堆积变得不稳定，并且 FK 相成为以恒定密度填充空间的最佳最小表面解决方案，同时最大化局部颗粒球形度。