Surface-dominated orientational dynamics and surface viscosity in confinedliquid crystals

A nematic liquid crystal in cylindrical pores of polycarbonate (Nuclepore) membranes with radii 25-400 nm was studied by dynamic light scattering. The fundamental mode of the orientational fluctuations shows a crossover from bulk behavior, dominated by bulk-elastic constant K, to a surface-dominated one, in which the relaxation rate is determined by the ratio of surface-an choring strength W and viscosity eta. In the smallest pores, the contributi on of surface viscosity zeta is also significant. The surface extrapolation length K/W goes approximately as (T - T-NI)(-1). The characteristic length for surface viscosity zeta/eta is of the order of 10 nm.