The Influence of High Pressure on the Discontinuity of the Isotropic - Nematic and the Isotropic — Smectic A Phase Transitions Studied by the Low-Frequency Nonlinear Dielectric Effect Measurements

Abstract

Results are presented for isothermal, pressure studies of the low frequency nonlinear dielectric effect in the isotropic phase of 8CB (isotropic — nematic (I-N) transition) and 12CB (isotropic — smectic(I-SmA transition). This made possible to determined the pressure dependence of the nematic and smectic clearing temperatures as well as the extrapolated temperatures of a hypothetical continuous phase transition up to P = 200 MPa. In the case of the I-N transition the discontinuity of the transition (ΔT) increases systematically with pressure while for the I-SmA transition ΔT decreases with rising pressure.

Key Words:

• clearing point
• nematic
• smectic
• high pressures
• nonlinear dielectric effect