Surface-induced reduction of twisting power in liquid-crystal films

Null transmission ellipsometry was employed to study the temperature evolution of the helical structure of the smectic-C(α)* phase. Free-standing films with thickness ranging from 31 to more than 400 layers were prepared and studied. The experimental results show a reduced twisting power in thin films. A simple model was constructed to explain the results. Surface effects were found to be the key reason for this phenomenon. Our findings are consistent with the theoretical studies of helically ordered magnetic films.