Observation of Molecular Orientation Induced by Capillary Wave

Abstract

A new technique was developed for inducing birefringence with the capillary wave in the subsurface region. The capillary wave accompanies a shear viscous flow underneath, and the flow causes a local orientational order of the molecules. The coupling between the shear flow and the molecular orientation can be interpreted in terms of the coupling viscosity µ, which is determined using the present technique. The experiment was carried out in the isotropic phase of 5CB. The observed anisotropy shows the decaying oscillation along the direction of the wave propagation, and the exponential decay into the depth. The measurement was also conducted by cooling the specimen to the critical point of the isotropic-to-nematic phase transition. The birefringence showed a critical behavior toward the virtual transition temperature. The critical exponent for Δn was determined to be 0.8, and that for µ 0.2.