Revealing the mechanism of the cooling-process on the performance of liquid crystal physical gels

Abstract

The formation of liquid crystal physical gels (LCPG) involves cooling process in which the gelators form fibers network through intermolecular physical cross-linking. However, the intrinsic correlation between the electro-optical properties of LCPG and cooling rate has rarely been fully discussed. In this report, an LCPG was constructed using 4-Cyano-4′-pentylbiphenyl (5CB) as the liquid crystal and 1,3:2,4-di-O-m,p-dimethylbenzylidene-D-sorbitol (DMDBS) as the gelator to investigate the intrinsic relationship between the cooling process and the performance of LCPG. By quantitative analysis the performance and morphology of LCPG at different cooling rate, it can be observed that a lower cooling rate induces reaction-limited aggregation, which promotes gelator diffusion and yields a denser gel fiber network characterized by smaller pore size and a higher number of pores, for instance, the size and number are 37.61 μm and 330, respectively, in LCPG's POM image at 5 °C/min cooling rate, whereas that of LCPG at 25 °C/min cooling are 89.09 μm and 108. It will reduce the off-state transmittance and promote the improvement of contrast ratio (CR), but bring about increase in driving voltage due to the larger anchoring energy of the network. In addition, we confirmed the better direct-current driveability of LCPG. Our work reveals the factors affecting the cooling kinetics on the performance of LCPG, and provides a new theoretical basis and technical support for the LCPG preparation.