Quasicritical behavior of dielectric permittivity in the isotropic phase of smectogenic n-cyanobiphenyls

Results are presented of temperature and pressure studies of static dielect ric permittivity (epsilon) and the nonlinear dielectric effect (NDE) in the isotropic phase of smectogenic n-cyanobiphenyls: 9CB, 10CB, and 12CB (4-cy ano-4'-n-alkylbiphenyl, n = 9, 10, and 12). For the mentioned properties, p retransitional effects can be well portrayed by applying the relations used for the isotropic phase of nematogens, where evidence of the quasicritical , fluidlike behavior with exponents alpha approximate to 0.5 and gamma=1 ex ists. This kind of behavior one can also observe on approaching the isotrop ic-smectic A transition NDE studies in 10CB and 12CB made it possible to de termine the pressure evolution of the discontinuity (Delta T) of the I-SmA transition, It was found that pressure first decreases the discontinuity of the transition, and that next a gradual rise appears. This behavior is unl ike the one observed for the isotropic-nematic transition, where only an in crease of Delta T with rising pressure was observed.