CONTROL OF MOLECULAR TILT ANGLES IN ORIENTED MONOLAYERS DEPOSITED BY A CHEMICAL ADSORPTION TECHNIQUE AND APPLICATION OF THE MONOLAYERS AS AN ALIGNMENT FILM

Oriented monolayers have been prepared from some chlorosilyl-type surfactants by a chemical adsorption (CA) technique for use as an alignment film in a liquid crystal cell. The monolayers were deposited from the mixture of one of three chlorosilyl-type surfactants having a long hydrocarbon chain (18-nonadecenyltrichlorosilane, nonadecyltrichlorosilane, and (19-(trimethylsilyl)-18-nonadecynyl)trichlorosilane) and the other having a short hydrocarbon chain ((3-bromopropyl)trichlorosilane). The molecular density of the monolayer, which affects the arrangement of the long hydrocarbon chain of the surfactants, was controlled by changing the composition ratio of the PTS in the mixture or by changing the scale of the outer functional group. The degree of molecular arrangement in the monolayers was investigated by IR spectroscopy, and tilt angles of the surfactants molecules in the monolayers were determined by measuring pretilt angles (alignment angles of liquid crystal molecules relative to the normal to the surface of the substrate) of the liquid crystal molecules injected into the liquid crystal cell, which was structured by using the monolayers as an alignment film. By changing the composition ratio of the mixture in the CA solution or an outer functional group of the surfactants having a long hydrocarbon chain in the molecules, the pretilt angles of the liquid crystal molecules could be controlled from 0-degrees to 15-degrees relative to the normal to the surface of the substrate. In order to interpret the experimental results, possible model structures in the monolayers have been proposed. Performance of the monolayers as an alignment film for a liquid crystal cell was evaluated further by driving the liquid crystal cells having the monolayers as alignment films. As the monolayers showed a fair degree of alignment effects without rubbing, this technique may be useful to prepare the alignment film for a liquid crystal cell.