Liquid Crystal Alignment on LB Films of Phthalocyanine Derivatives

It has been found that contrast ratio of nematic liquid crystal (LC) on phthalocyanine (Pc) derivative Langmuir-Blodgett (LB) film cell has a correlation with dichroic ratio of the LB film. These results show that this homogeneous alignment force is originated from orientation of rod-like aggregates of the Pc derivative. On the other hand, the LC alignment changes from uniform homogeneous alignment to uniform homeotropic alignment through non-uniform tilted alignment, with the increase of the number of side chain carbon atoms of the Pc derivative. Such alignment change has been also observed with the increase of concentration ratio of a long side chain Pc in a mixed Pc LB film. These show that homeotropic alignment force originates from the ordered long side chain. Therefore, LC alignment is determined by Pc orientation and side chain length, and the feasibility of the tilted LC alignment is shown.