Optical Kerr effect in the isotropic phase of various alkyl-cyanobiphenyl homologues

Measurements have been made of the optical Kerr effect on four homologous members of the alkyl-cyanobiphenyl series of liquid crystals at temperatures above the nematic-to-isotropic clearing temperatures. Amplitudes of the birefringence and rotational relaxation times (τ) have been recorded as the temperature was increased from just above the clearing temperature for each system. From the data it was found that the optical Kerr constant B 0 had a temperature dependence of (T - T*)-1, similar to that predicted by the Landau-de Gennes equation. This persisted only for a very limited temperature range of a few degrees Celsius. Beyond this range, and for all samples, the existence of an additional temperature independent contribution to B 0 was evidenced.