Dielectric studies on strongly polar discotic liquid crystals

Abstract

We report dielectric investigations on the fourth and fifth homologues of the series I-nitro- 2,3,6,7,10,1 I-hexaalkoxytriphenylene. A hexagonally ordered columnar mesophase (Dho) is exhibited by both the compounds but the fourth homologue shows in addition, a more ordered mesophase at lower temperatures. The dielectric constants observed are high compared to the values observed in other discotic materials. In the frequency range studied (1 Hz- 1 MHz) one relaxation mode is observed in the Dh0 phase which can perhaps be correlated with a glass transition. A strong reduction in the magnitude of the relaxation frequency and an associated increase in the dielectric strength of the mode are observed at the transition from Dho to the lower temperature phase. The data in the two-phase region of this first-order transition are also presented.