The polar anchoring strength coefficient $W$ and polar pretilt angle ${\theta }_0$ were measured simultaneously for the liquid crystal pentylcyanobiphenyl at a rubbed polyimide alignment layer that is ordinarily used for vertical alignment. It was found that $W\propto {\theta }_0^2$ over the range $0°\le {\theta }_0\lesssim 35°$. The results provide a confirmation of the dual easy axis model, wherein the liquid crystal director adopts an equilibrium orientation ${\theta }_0$ at the substrate that is determined by competition between a pair of preferred orientation directions.

• Received 20 October 2004

DOI:https://doi.org/10.1103/PhysRevLett.94.057802