Investigation of surface phenomena in the liquid crystal-orienting coating system

Abstract

on there is a wide asymmetric absorption band with a maximum at 3420 cm -~, which characterizes an intermolecular hydrogen bond and indicates the presence of sorbed water molecules on the surface of the film. This is confirmed by the presence of a weak band from the deformation vibrations of adsorbed water molecules at 1635 cm -~, a displacement of which toward lower frequencies is characteristic in adsorption onto Mg-containing compounds [4]. It is to be noted that the absorption band at 3420 cm -I is also observed in the spectra of BHAB on MgF2, while it is practically absent in the spectra of BHAB on NaCI (Fig. la). The deposition of a liquid crystal onto the surface of a film of magnesium flurode somewhat changes the spectral characteristics of the indicated absorption band. The decrease in band width with a certain increase in its intensity may indicate a reaction of BHAB molecules with surface chemical groups of the backing. Involvement in such an interaction shows up primarily in the vibrations of molecules in the surface layers, the proportion of which is relatively small with respect to the entire layer. Nevertheless, considering the specific properties of liquid crystals, it may be expected that a change in the character of interaction of surface layer molecules with the backing surface will exert a definite effect on the whole system. This is connected first of all with the orientation of the BHAB molecules, since a change in the chemical nature of the surface will lead to a change in the direction of the interaction of BHAB with the surface groups of the backing, and correspondingly to participation of different functional groups or atoms of the molecule in this interaction. A predominant involvement of any of these functional groups in interaction with the chemical groups of the surface will lead not only to a change in the spectral characteristics of the surface layers, but also can become the reason for larger-scale changes, caused by a change in the orientation of the molecules of these layers, and also by the presence of a remote orientation order in liquid-crystalli ne systems. This is caused by the fact that, as a result of interaction with active centers of the surface, the molecules of the surface layers of the liquid crystal which form adsorbed monolayers will be in a more stable "bonded" state. The appearance of adsorption forces will also cause a certain increase in the anisotropy of the free vibrations of molecules in the layers adjacent to them, aiding in the formation of local