Structure and Phase Transitions in Partially Confined Smectic Liquid Crystals

ABSTRACTWe present the results of an X-ray scattering study on partially confined smectic-A (layered) LC films. This partial confinement is achieved by placing the LC material inside the open grooves of a glass grating. Samples prepared in this manner are confined in the direction perpendicular to the gratings. Samples in which the LC is contained entirely inside the grooves develop an induced molecular tilt, which results in a compression of the smectic layers. The molecular tilt varies as the amount of the LC material increases, eventually forming a thin overlayer film above the gratings. As the thickness varies, a second region develops in the films. The layer spacing in this region is close to the bulk layer spacing. This structural evolution is coupled to a variation in the nematic-to-smectic-A phase transition temperature of the samples from the bulk. In addition, the nature of the phase transition is driven first order. The effects of partial confinement on a sm-C* LC film is discussed briefly.