Bicontinuous Double-Diamond Structures Formed in Ternary Blends of AB Diblock Copolymers with Block Chains of Different Lengths

Abstract

We report on the formation of a bicontinuous double diamond (DD) structure in ternary blends of poly(styrene-b-isoprene) (SI) diblock copolymers with chains of different lengths merely in a polyisoprene block. Certainly, the materials revealing the DD structure with mesoscopic length scale have strongly been expected due to high potential for applications; however, it is difficult to form owing to thermodynamically evident disadvantages such as wider surface area and larger domain thickness variation, particularly for monodisperse copolymers. The DD structure was successfully formed for ternary blends composed of three parent diblock copolymers; SI-L (M = 190k, φs = 0.46), SI-G (M = 151k, φs = 0.62), and SI-C (M = 124k, φs = 0.73), resulting in covering the overall composition range 0.57 ≤ φs ≤ 0.60, where φss denotes volume fractions of polystyrene blocks. Four-branched double network structure with space group symmetry of Pn3m was clearly proved by transmission electron microscopy (TEM) observation aid...