Surface-Dominated Orientational Dynamics and Surface Viscosity in Confined Liquid Crystals

Abstract

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-anchoring strength $W$ and viscosity $\ensuremath{\eta}$. In the smallest pores, the contribution of surface viscosity $\ensuremath{\zeta}$ is also significant. The surface extrapolation length $K/W$ goes approximately as $({T\ensuremath{-}T}_{\mathrm{NI}}{)}^{\ensuremath{-}1}$. The characteristic length for surface viscosity $\ensuremath{\zeta}/\ensuremath{\eta}$ is of the order of 10 nm.