Anomalous Behavior of Helicoidal Pitch in Surface Induced Transition from Winding of Unwinding Chiral Smectic C

We have studied the thickness dependence of helicoidal pitch in order to understand the mechanism of the structural change from winding to unwinding chiral smectic C phase. The pitch and critical thickness were measured for various temperatures using wedge type cells with the wedge angle varied from 0.06 to 0.21°C. Thickness and temperature dependence of the pitch have divergent tendencies toward certain respective thicknesses and temperatures. It is considered that the unwinding phase in the thin cell is not smectic A but chiral smectic C. A surface induced reentrant-like phenomenon similar to that field induced is observed.