Results are presented of temperature and pressure studies of static dielectric permittivity (ɛ) and the nonlinear dielectric effect (NDE) in the isotropic phase of smectogenic n-cyanobiphenyls: 9CB, 10CB, and 12CB ${(4-\mathrm{c}\mathrm{y}\mathrm{a}\mathrm{n}\mathrm{o}-4\mathrm{}}^{\prime }$-n-alkylbiphenyl, $n=9,$ 10, and 12). For the mentioned properties, pretransitional 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 $\alpha \approx 0.5$ and $\gamma =1\mathrm{}$ exists. This kind of behavior one can also observe on approaching the isotropic–smectic A transition. NDE studies in 10CB and 12CB made it possible to determine the pressure evolution of the discontinuity $\left(\Delta T\right)$ of the $I-\mathrm{Sm}A$ transition. It was found that pressure first decreases the discontinuity of the transition, and that next a gradual rise appears. This behavior is unlike the one observed for the isotropic-nematic transition, where only an increase of $\Delta T$ with rising pressure was observed.

• Received 26 July 1999

DOI:https://doi.org/10.1103/PhysRevE.61.5349