Kerr effect and the nonlinear dielectric effect on approaching the critical consolute point

Abstract

For the exponent \ensuremath{\psi}, which describes a critical anomaly of the nonlinear dielectric effect (NDE) and the electro-optic Kerr effect (EKE) in critical solutions, theoretical models predict ${\mathrm{\ensuremath{\psi}}}_{\mathrm{NDE}}$=${\mathrm{\ensuremath{\psi}}}_{\mathrm{EKE}}$=${\mathrm{\ensuremath{\psi}}}_{\mathrm{theor}}$=\ensuremath{\gamma}-2\ensuremath{\beta}. An experiment gave ${\mathrm{\ensuremath{\psi}}}_{\mathrm{NDE}}$ (\ensuremath{\simeq}0.37)${\mathrm{\ensuremath{\psi}}}_{\mathrm{theor}}$ (\ensuremath{\simeq}0.59)${\mathrm{\ensuremath{\psi}}}_{\mathrm{EKE}}$ (\ensuremath{\simeq}0.85). For all other experimental results, however, the agreement with the theory is good. In this paper it is shown that also both of the above relations may be valid. This result is based on the assumption that the NDE and the EKE exhibit a mixture of both a nonclassical and a classical type of behavior of critical fluctuations. Additionally, a relation was found between the semimicroscopic models for critical solutions and the phenomenological Landau--de Gennes model for the pretransitional effect of the NDE and the EKE in the isotropic phase of nematogens.