Time evolution of the structure of confined Sm-C^* films

The structural evolution of films of the liquid crystal mixture mx5112 in the Sm-A and Sm-C^* phases has been studied using X-ray scattering techniques. Liquid crystal (LC) films spread on glass substrates with relief grating of 10 μm period are subjected to competing boundary conditions on opposite sides. On one side, the LC-air interface imposes a homeotropic boundary condition while on the other the glass substrate with grating generally imposes a homogeneous boundary condition. Near room temperature, the smectic layer normal is oriented parallel to the grating lines on the substrate. The measured smectic layer spacing reveals oscillations between a Sm-C^* and a Sm-A like structures which depend on the film thickness as well as the distance from LC-air interface and is attributable to the difference in the molecular tilt imposed by a. the air-LC interface; b. the substrate; and c. the gratings' internal walls.