Smectic ordering in confined liquid crystal films: A depth study

Grazing incidence x-ray scattering was used to study the structure of films of a room temperature smectic-C* mixture, deposited on glass substrates, that consisted of gratings with a 9 μm period. There is evidence for the presence of two regions of confinement as function of film thickness. The first region, of thickness ranging from 1 to 5 μm, is dominated by the size and depth effects of the individual grating grooves. The second region, of thickness ranging between 5 and 20 μm, is dominated by the cooperative alignment effect of all the grooves in the grating and the grating density. Finally, the structural evolution has been studied as a function of depth in the film for samples between 1 and 20 μm by changing the incidence angle. We find that for films between 10 and 20 μm this structural evolution is equal to the structural evolution observed as a function of film thickness.