Thickness Dependent Phase Behavior of Antiferroelectric Liquid Crystal Films

Free standing films of a liquid crystal compound with simple surface enhanced order were studied. The resultant phase diagram demonstrates that (1) the short helical pitch smectic-C_α^* phase disappears below a film thickness of 10 layers, and (2) the temperature window of a distorted 4 layer smectic-C_FI2^* phase increases dramatically upon decreasing film thickness. The experimental findings were attributed to the reduced dimensionality and enhanced surface effects in thin films. The results of the smectic-C_α^* phase are consistent with what have been reported for helically ordered magnetic thin films, with a noticeable difference due to the opposite effect of the surface on ordering in the two systems.