From columns to networks : search toward the elusive single gyroid with π-shaped polyphilic liquid crystalline block molecules

Abstract

Polyphilic block molecules form a wide range of new liquid crystalline (LC) phases with complex morphologies on a nanometer scale. Herein the soft self-assembly of π-shaped p-terphenyl-based bolapolyphiles having two adjacent aliphatic side chains at the central benzene ring (catechol dialkyl ethers) is reported with a focus on the design of single-network structures. Depending on the length of the side chains and temperature a series of polygonal honeycombs, a zeolite-like LC, a lamellar phase, and two segmented network phases with cubic symmetry is found. In these networks self-assembled glycerol spheres, forming the junctions, are interconnected by coaxial p-terphenyl bundles. Upon side-chain elongation, a double-gyroid phase with three-way junctions is replaced by the single diamond having a four-way junction network. However, the single gyroid supposed to be formed by further side-chain expansion could not be observed; instead, the LC self-assembly breaks down completely. It is hypothesized that the formation of single-network phases by bottom-up self-assembly in soft matter systems requires a minimum junction valence of at least 4 to stabilize the networks.