Design and phase transition behavior of siloxane-based monomeric and dimeric liquid crystals bearing cholesteryl mesogenic groups

摘要

A series of siloxane-based monomeric and dimeric liquid crystals (LCs) bearing cholesteryl mesogenic groups were newly synthesized and their phase transition behavior was investigated by polarized optical microscopy (POM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). All the siloxane-based LCs obtained in this study showed a smectic A phase in a wide temperature range. Among the siloxane-based LCs obtained, only the dimeric LC with a shortest siloxane unit at a central part of a spacer was found to exhibit a chiral nematic phase and a blue phase in addition to the smectic A phase. The difference in the thermal properties of the siloxane-based dimeric LCs was investigated in terms of their conformations. Furthermore, the results obtained for the siloxane-based LCs were discussed with comparing with those of homologues having the normal alkyl chains and spacers. (c) 2019 Elsevier B.V. All rights reserved.