Phase transition to anticlinic texture in free-standing smectic C films

Experimental data on the optical reflectance of free-standing smectic C fil ms were analyzed within the framework of a phenomenological Landau approach . At a certain temperature T-0N (determined from experimental data), which exceeds the known temperature T-c of the volume phase transition from smect ic A to smectic C state, a surface phase transition takes place whereby mol ecules in the surface layer become sloped relative to the normal of the sme ctic layers. The transition temperatures T-0N(s,a) for N-layer films posses sing synclinic (symmetric) and anticlinic (antisymmetric) textures of the o rder parameter (tilt angle theta) were determined. A comparison of the theo retical and experimental data allowed all parameters of the model to be det ermined (including critical indices of the correlation length and the surfa ce order parameter). Three possible models of the transition from the state with transverse polarization (perpendicular to the molecular tilt plane) t o the state with longitudinal polarization (parallel to this plane) are ana lyzed. The transition takes place at low (1 degrees -2 degrees) values of t he order parameter theta in the middle layer of the film. (C) 2001 MAIK "Na uka/Interperiodica".