Collective fluctuations and wetting in nematic liquid crystals

The role of wetting in the dynamics of collective orientational fluctuations in confined nematic liquid crystals is examined by analyzing the spectrum of normal modes in planar geometry bounded either by disordering or ordering substrates. The heterophase nature of the equilibrium configurations occurring in the vicinity of the nematic-isotropic phase transition gives rise to a localized slow mode, which corresponds to fluctuations of thickness of the (dis)ordered boundary layer and becomes soft if the wetting is complete. In addition, a few modes restricted to the boundary layer—director modes in case of ordering substrate, and biaxial modes in case of disordering substrate—also exhibit pretransitional slowdown provided that the surface interaction is strong enough. Analogous behavior of fluctuations is expected in other wetting geometries, e.g., in the case of a substrate-stabilized smectic boundary layer in nematic and isotropic samples.