Phase transitions from the isotropic liquid to liquid crystalline mesophases studied by linear and nonlinear static dielectric permittivity

Results of studies of static dielectric permittivity (epsilon) and nonlinea r dielectric: effect (NDE) in the isotropic phase of 4-n-4'-isothiocyanatob iphenyl (nBT) homologous series from n = 2 to n = 10 exhibiting the isotrop icsmectic E (I-SmE) transition, are presented. They are compared with resul ts of similar studies in 4-cyano-4-n-alkylbiphenyls (nCB) from n = 4 to n = 12. In this homologous series isotropic-nematic (I-N) and isotropicsmectic -A (I-Sm-A) transitions take place. Despite significant differences between N, Sm-A, and Sm-E phases the same pretransitional behavior of E and NDE in the isotropic phase, described by critical exponents gamma = 1 and alpha = 0.5. was found. It has been shown that when the length of the alkyl chain of a compound increases the discontinuity of the transition drops in nBT an d rises in nCB. The influence of pressure on the discontinuity is also disc ussed.