Self-Assembly of a Liquid Crystalline Anisotropic Gel

Abstract

A new azobenzene-containing gelator for low-molar-mass liquid crystals (LCs) was synthesized. It can effectively gel nematic LCs such as E7 through the formation of a hydrogen-bonded network. Moreover, an intriguing self-assembly process was observed. When thin films of the E7/gelator mixture, cast on CaF2 crystal windows or glass slides, are cooled from the isotropic phase, at temperatures below but close to the sol−gel phase transition, aggregation of the gelator starts from the edge of the film, and the fiberlike aggregates grow predominantly normal to the edge, leading to the formation of an oriented network at the macroscopic scale in the liquid gel state. On further cooling through the phase transition from liquid gel to nematic gel, the aligned fiberlike aggregates induce a long-range molecular orientation of E7, in the direction perpendicular to the fibers. The end result of this is a self-assembled anisotropic LC gel formed in the absence of any external effects such as surface treatment for the substrates or irradiation for the azobenzene groups on the gelator molecules.