Orientation of nematics on metallic liquid surface

Abstract

Reports experimental results about director orientation of some nematic compounds deposited on metal which is in liquid phase. The interference figure of a reflective birefringent wedge allows a precise determination of the thickness averaged extraordinary index of refraction. The authors calculate this averaged index as a function of the two anchoring angles of the nematic at the two interfaces: this relation, the measure of the averaged index, and one of the anchoring angles, allows one to obtain the value of the second anchoring angle-here the nematic-metal one. With this method, the authors find that the PAA director is normal at nematic-gallium interface, whereas the MBBA and 5CB one lies in interface plane. The authors have observed, for MBBA, an orientation induced by gallium oxide. These results are checked and agree with theoretical forecasts concerning nonsymmetric nematic film orientation. The critical thickness can be evaluated from the interference figure: if this exists, its value is less than one micrometer for MBBA in the studied geometry.