Use of a gelator in a ferroelectric liquid crystal: pitch compensation and nanofibres

Abstract

A new azobenzene-containing gelator for liquid crystals, AG2, was synthesized and used to prepare a ferroelectric liquid crystal (FLC) gel. The FLC gel shows interesting features. On cooling from the isotropic phase into the N* phase, the dissolved AG2 acts as a chiral dopant and has a compensation effect on the helical pitch of the N* phase. With 0.5 wt% of AG2 in the FLC host, a homogeneous alignment of the FLC molecules is formed in the N* phase, ensuring the bulk alignment in the SmC* phase, even on quenching the mixture from the isotropic phase. This alignment under fast cooling contrasts sharply with the slow cooling rate required for the alignment of a pure FLC. After formation of the bulk alignment, the aggregation of AG2 occurs in the lower temperature SmA or SmC* phases, and the gelator molecules self-assemble into nanometer-sized fibres (about 100nm diameter) that are aligned and located between the smectic layers. As the gelator is microphase-separated from the FLC in the SmC* phase, it exerts little disruption on the electro-optic properties of the FLC cell.