MEASUREMENT OF THE ELASTIC-CONSTANTS AND EFFECTIVE SURFACE ANCHORING ENERGY FOR A SMECTIC-C LIQUID-CRYSTAL

Optical extinction angle spectra of a pyrimidine smectic c material in the surface stabilised geometry have been measured as a function of a pplied ac electric field and temperature, The results were fitted usin g a model which assumes uniformly tilted layers either side of a infin itely anchored chevron interface. The model presented uses the free en ergy expression of Leslie et. al.(1) to calculate the liquid crystal c -director profile through the cell and Jones calculus to determine the associated optical properties. With no applied voltage this gives a s tructure very similar to a triangular director profile An applied ac v oltage couples to the dielectric biaxiality causing director reorienta tion in the bulk of the cell, At increased voltages an excellent fit i s obtained by allowing movement of the director at the surface, This s urface movement is described by inclusion of finite surface anchoring in the model, Tile fits give the c-director bend (B-1) and splay (B-2) elastic constants and the effective surface anchoring as a function o f temperature.