Refractive Indices, Dielectric Constants, and Order Parameter of Four Alkyl/Alkoxyphenylcyclohexanecarboxylate Liquid Crystals in the Nematic Phase

Abstract

Abstract The extraordinary and ordinary refractive indices, ne and no and the densities of four liquid crystals 4-pentylphenyl trans-4′-pentylcyclohexanecarboxylate, 4-ethoxyphenyl trans-4′-propylcyclohexanecarboxylate, 4-ethoxyphenyl trans-4′-butylcyclohexanecarboxylate, and 4-methoxyphenyl trans-4′-pentylcyclohexanecarboxylate have been reported at different temperatures. The effective polarizabilities αe and αo in the nematic phase have been calculated using 1) Neugebauer and 2) Vuks methods. The order parameter S calculated from the two methods were comparable. The dielectric constants ε|| and ε⊥, parallel and perpendicular to the long axis of the molecules have been measured at 1 kHz at different temperatures. The order parameters for the liquid crystals were then evaluated from dielectric anisotropy Δε(=ε||−ε⊥), polarizability anisotropy Δα(=αe−αo) and dipole moment μ, using Maier and Meier equation and were found only slightly less than those obtained from refractive indices method. It was concluded that Maier and Meier equation also could be used to evaluate the order parameter of liquid crystals of molecules having dipole moments 2 Debye or less.