Dielectric and high-pressure investigations on a thermotropic cubic mesophase.

Optically isotropic cubic mesophases, which are commonly exhibited by lyotropic materials, have been observed in a few thermotropic liquid crystalline systems also. Although the first thermotropic cubic mesophase was reported about 40 years ago, its existence in diverse systems is only a recent finding. Moreover, the investigations on this mesophase have mainly concentrated on the structural aspects. While the effect of pressure has not been reported, only one dielectric measurement seems to have been carried out. In this paper we present the results of our dielectric and high pressure investigations on a compound exhibiting a thermotropic cubic mesophase. Two salient results are (i) a low frequency relaxation mode is observed with a large dielectric strength with appreciable changes across the columnar-cubic and cubic-smectic C transitions; and (ii) the cubic phase ceases to exist when the applied pressure exceeds about 400 bar.