NONLINEAR DIELECTRIC EFFECT BEHAVIOR IN A CRITICAL AND NEAR-CRITICAL BINARY MIXTURE.

Experimental results are presented of the nonlinear dielectric effect (NDE) studies in the homogeneous phase of critical and near-critical binary mixtures. Both the stationary NDE and the related dynamic properties are discussed. In a critical mixture the NDE stationary response is described by a critical exponent psi approximate to 0.4 near the critical consolute temperature(T-C) and psi approximate to 0.6 remote from T-C. For the noncritical mixture the exponent describing the temperature behavior near T-C decreases down to psi approximate to 0.1. The temperature behavior of the NDE decay after switching off a strong electric field is described by the exponent y = 1.3 for a critical mixture and y -> 1 for a non-critical mixture. The possible explanation of the observed phenomena is proposed. It assumes the appearance of a quasi-nematic structure induced the external field, leading to the appearance of mean-field properties in the vicinity of T-C. The possible relationship with the behavior observed in a critical mixture under shear-flow, for instance when testing the anomaly of shear viscosity, is also shown.