Kerr effect in the critical solutions of propionitrile

The electrooptical Kerr effect (EKE) has been measured in four critical propionitrile-hydrocarbon systems covering a wide range of refractive indices as well as the density mismatch between the components. Precritical EKE anomalies are strongly solvent-dependent and they have been observed only in the mixtures with distinctly pronounced critical opalescence and different electric permittivities of the components. The solvent influences the critical amplitude, but not the critical exponent, the latter being close to 0.7 for the examined systems. The possible mechanisms of the field-induced optical anisotropy of the solutions are discussed.