High pressure studies on a nematogen with highly polar molecules: Evidence for a nematic–nematic transition

Abstract

We have modified a high pressure optical set-up to enable measurements on the optical path difference of aligned liquid crystals. We present the phase diagram of a polar nematogen, viz. p-cyanophenyl p-n heptylbenzoate which is shown to exhibit a nematic (Nd) to nematic (N1) transition in the bulk at elevated pressures. We have also measured the temperature variations of the orientational order parameter (S) at various pressures to find that S has constant values at both the nematic to isotropic and Nd to N1 transitions at different pressures