The hydrodynamics of surface layers of nematic liquid crystals studied by modulation ellipsometry

(Received 14 February 1990, revised 26 November 1990, accepted 17 January 1991)

Abstract
An acoustically induced Poiseuille flow changes the director orientation of a nematic liquid crystal in a hybrid cell. Thin surface layers (less than 0.2 ) in the vicinity of solid interface are of special interest. To study them we used a novel technique of modulation ellipsometry based on probing of the interface layers by an evanescent optical wave appearing in a liquid crystal when light is totally reflected from the interface between the liquid crystal and heavy glass. The essential details of the technique are : the angle of light incidence is considerably higher than the total reflection angle and the a.c. acoustic excitation is used with a consequent lock-in detection of the response. The technique allows us to measure both the dynamic deviation angle and the static tilt angle of the director at the homeotropically orienting interface. As a result, temperature dependence of the anchoring energy for that interface was measured.