Linear and nonlinear dielectric studies in the isotropic and smectic E phases in 4,4-alkyl-4′-isothiocyanatobiphenyl

Results are presented of studies of linear and nonlinear dielectric measurements in the isotropic, smectic E phase in 4,4-alkyl-4'-isothicyanatobiphenyls (4BT). The mean-field behaviour was valid up to the smectic E phase transition. In the smectic E phase the Vogel-Fulcher law describes temperature and pressure dependences of the relaxation time. An analysis of the higher temperature relaxation time data led to predictions of the mode coupling theory with the power law universal function tau = A(T - T-C)(gamma), where gamma = -3.3, T-C = 288 +/- 15 K. Increase of pressure brings the epsilon" curve closer to the Debye shape.