Study of Orientation and Order of Non-mesogenic Solutes in Liquid Crystalline Matrix by Infrared Spectroscopy

Abstract

The orientation and order of molecules of solutions containing a non-mesogenic solute, n-alkylbenzenes and halobenzenes, in the nematic solvent N-(p-ethoxybenzylidene)-p'-n-butylaniline, EBBA, were investigated by the measurement of the intensity of the absorption bands in the infrared region of both homogeneous and homeotropic aligned samples. The results show that the decrease of the nematic-isotropic transition temperature, T_c, depends on the size and shape of the non-mesogenic guest molecules. Increasing length of the flexible end chain (n-alkyl group) of the n-alkylbenzene homologous series decreases T_c of the mesomorphic mixture. Increasing the size of the atomic radius of the halogen atom of the halobenzene homologous series also decreases T_c of the mixture. Since the order parameter of host molecules depends on the cell preparation, the order parameter of the dissolved n-alkylbenzenes and halobenzenes was evaluated for a constant solvent order. Plotting these results against the number of C-atoms of the alkyl side chain shows an odd-even effect. The order parameter of halobenzene guest molecules decreases slightly with increasing radius of the halogen atom.