Fluidlike behavior of dielectric permittivity in a wide range of temperature above and below the nematic-isotropic transition.

Abstract

Singular behavior of the static dielectric permittivity of n-alkyloxycyanobiphenyls (CnH2n+1O-Ph-Ph-C [triple bond] N, n=6, 7) was studied above and below the nematic clearing point (T(I-N)). On approaching the clearing point, the evolution of principal components of the nematic permittivity tensor, epsilon(parallel) and epsilon(perpendicular), is described by the order parameter exponent beta approximately 0.25. The mean value of the nematic permittivity epsilon(mean)=(epsilon(parallel)+2epsilon(perpendicular))/3 exhibits a singular behavior similar to that observed in the isotropic phase and that for the diameter of the coexistence curve in binary mixtures. The derivative of experimental data d(epsilon)iso(T)/dT and d(epsilon)mean(T)/dT shows the specific-heat-like behavior with universal exponents alpha=alpha' approximately 0.5. Results obtained confirm the hypothesis of the fluidlike, pseudospinodal, and tricritical behavior of the isotropic to nematic phase transition. [A. Drozd-Rzoska, Phys. Rev. E 59, 5556 (1999)].