Supramolecular Self-Assembly of Filamentary Structures from Bent-Core Liquid Crystals

We have used small angle x-ray scattering (SAXS) and freeze fracture transmission electron microscopy (FFTEM) to characterize a novel filamentary phase of bow-shaped liquid crystals (LCs) with nanophase segregating properties. Bow-shaped LCs with a rigid core and a flexible trisilane-terminated alkyl tail self-organizes into filamentary structures upon cooling from conventional orthogonal bent-core smectic phases. The formation of filamentary structure is driven by nanophase segregation and influenced by the length of alkyl linker between the core and trisilane unit. Nanophase segregation occurs because the core of the molecule is immiscible with its trisilane tail. We performed systematic SAXS studies to investigate the formation of nanofilaments in a homologous series of bow-shaped molecules consisting of n-carbon alkyl linker (5 < n < 11). We find that the homologues with n > 9 (longer tail) have a strong tendency to self-assemble into a fully bilayered nanofilament structure, while for n < 8 (shorter tail) the LCs tend to retain their partial bilayered structure also seen in the SmA phase. We propose a nanoscale model to explain the structural changes and the filament formation.