AN OPTICAL STUDY OF THE INTERFACIAL REGION OF A SURFACE-ALIGNED NEMATIC LIQUID-CRYSTAL

The optical reflectivity from the interfacial region of a nematic/ solid wall boundary has been measured as a function of incident angle and temperature for 7CB. Considerable deviation from Fresnel reflectivity occurs for the E-ray whereas reflectivities for the O-ray are similar to Fresnel. To fit the experimental data an interfacial region having a density approx. 1 1/2% greater than bulk as well as an increase of order parameter by 10-20% is required. The skindepth of the region obtained is approx. 850 A. It is postulated that a quasi-smectic layer exists near to the boundary wall.