The optical and electrical Kerr effect in 4-n-pentyl-4′-cyanobiphenyl

Abstract

The optical and d.c. Kerr constants have been measured in the isotropic phase of 4-n-pentyl-4′-cyanobiphenyl (5CB) as a function of temperature and in 5CB/CCl₄ solutions as a function of concentration. By using the pulsed method dynamic properties have been determined. From the solution measurements the permanent dipole moment and optical polarizability have been determined and a critical concentration behaviour observed. The predictions of the Landau-de Gennes model for pretransitional behaviour have been examined in the isotropic phase and it has been shown from both the Kerr constants and relaxation analysis that Δn and τ are proportional to (T - T*)^-1. From these results we have determined the phenomenological constant a, the viscosity coefficient v, the theoretical second order transition temperature T* and (T _c - T*). From the differences in the relaxation data between the d.c. and optical field induced ordering we have inferred a size polydispersity for the cybotactic groups.