Gelled lyotropic nematic liquid crystals

Lyotropic liquid crystal gels (LLC gels) are versatile materials which combine the anisotropy of a liquid crystal with the mechanical stability of a gel. We succeeded in gelling the rare calamitic nematic N-C phase of two different micellar LLC systems with the low molecular weight gelator (LMWG) 3,5-bis-(5-hexylcarbamoyl-pentoxy)-benzoic acid hexyl ester (BHPB-6). The systems of choice are: (1) a binary LLC system with the surfactant N,N-dimethyl-N-ethyl-1-hexadecylammonium bromide (CDEAB) and water; (2) a ternary LLC system with the surfactant N,N,N-trimethyl-N-tetradecylammonium bromide (C(14)TAB), n-decanol, and water. The obtained gels show optical birefringence and no macroscopic flow. Freeze fracture electron microscopy (FFEM) images show ribbon-like gel fibres that form the gel network and can stack into thicker bundles, while small-angle X-ray scattering (SAXS) confirms the coexistence of the nematic N-C phase and the gel network. The growth of the gel network was monitored with time-resolved SAXS measurements. Additionally, significant gel ageing effects were observed in rheology measurements, showing that the gel strengthens with time. With this study, we considerably broaden the pool of available surfactant-based LLC gels and pave a way to macroscopically aligned LLC gels with the goal to apply them as stimuli-responsive actuators and sensors.

Automated summary

Lyotropic liquid crystal gels (LLC gels) with the anisotropy of a liquid crystal and the mechanical stability of a gel were successfully prepared by gelling the rare calamitic nematic N-C phase of two different micellar LLC systems with a low molecular weight gelator (LMWG). The obtained gels exhibited optical birefringence and no macroscopic flow, and microscopic analysis confirmed the coexistence of the nematic N-C phase and the gel network. The growth of the gel network was monitored, and rheology measurements showed significant gel ageing effects. This study expands the range of surfactant-based LLC gels and paves the way for their application as stimuli-responsive actuators and sensors.