Dielectric Method of Determination of the Association Energy Between Polar Molecules in Nematic Liquid Crystal

Abstract

Effective values of the parallel and perpendicular components of the molecular dipole moment per one molecule have been calculated for the 5CB compound, from the values of the parallel and perpendicular components of the dielectric permittivity tensor, using Maier and Meier equations. Necessary molecular parameters, such as transverse and longitudinal polarizabilities, as well as temperature dependence of nematic order parameter for 5CB, have been calculated from ordinary and extraordinary refractive indices and density. In this case Neugebauer equations, combined with Haller extrapolation procedure, have been used. The calculated values of effective dipole moment are much lower than for an isolated molecule. This effect decreases with increasing temperature. This has been regarded as an evidence of the antiparallel association occurrence in 5CB. Obtained results and discussion, on the basis of van't Hoff equation, allow determination of equilibrium constant K(T) and association energy ΔE.