SYNCHROTRON X-RAY STUDY OF DIMENSIONAL CROSSOVER IN SOLID-PHASE SMECTIC LIQUID-CRYSTAL FILMS

The crystalline phases of the liquid crystal 8OSI [racemic 4-(2'-methylbutyl)phenyl 4'-(octyloxy)-(1,1')-biphenyl-4-carboxylate] have been studied using high-resolution synchroton x-ray-scattering techniques. A careful analysis has been performed on the x-ray-scattering profiles of samples with thicknesses varying from 1000 molecular layers to five layers. Three-dimensional long-range positional order with large-amplitude thermal fluctuations is observed for a very thick film. As the thickness is decreased, two-dimensional characteristics become apparent. The scattering profiles of thin films are described by the power-law line shape, 1/[Q-G]2-eta(eff), with an effective exponent-eta-eff, which evolves with thickness.