Orientational ordering in thin interlayers of nematic liquid crystal 4,4'-penthyl-cyanobiphenyl

The method of polarization IR-spectroscopy was applied to investigate the change of structure of nematic liquid crystal 5CB interlayers between fluorite plates at the transition from a bulk to a thin-film state. For the analysis of spectroscopic data a two-fraction model allowing the determination of the orientation and the degree of ordering of the transition moments of intramolecular bonds is developed. It is shown that the complete description of structural changes should include the characteristics of ordering of fragments of molecules both on the angle of the director inclination, and on a direction in a plane parallel to the film-substrate interface. It is established that the decrease of the liquid crystal layer thickness in the investigated system is accompanied by a transition of the biphenyl core orientation from inclined to homogeneously planar with increase of a directionally ordered fraction of the molecules, and by freezing of the internal rotation of the methyl group