Results are presented for high-pressure, isothermal studies of the low-frequency nonlinear dielectric effect (LF NDE) in the isotropic phase of n-octylcyanobiphenyl (8CB, isotropic-nematic liquid crystal phase transition) and n-dodecylcyanobiphenyl (12CB, isotropic–smectic-A phase transition). In both cases a linear pressure dependence of reciprocals of LF NDE, with no distortions near the clearing point, was found. This behavior is in agreement with classical relations derived from the Landau–de Gennes model. The pressure dependence (up to 100 MPa) of clearing temperatures and temperatures of extrapolated, hypothetical, continuous phase transitions were determined. For 8CB isothermal pressure and isobaric temperature pretransitional effects have been superimposed on one scaling curve. This makes it possible to investigate the pretransitional effects under high pressure from temperature measurements carried out under atmospheric pressure.

• Received 30 September 1996

DOI:https://doi.org/10.1103/PhysRevE.55.2888