WEAK ANCHORING OR PRETILT

The average molecular orientation in a nematic liquid crystal sample s ubmitted to an external field is analyzed assuming strong anchoring. i t is shown that if a small constant pretilt angle at the surface is ac tually present, an apparent extrapolation length can be measured. This could lead to the conclusion that the anchoring is weak, despite the fact that the anchoring is truly strong. This conclusion remains valid even if the pretilt angle is so small that it cannot be detected by u sual optical methods. An expression connecting the apparent extrapolat ion length with the pretilt angle is deduced. It is shown that a tilt angle of the order of pi/180 rad gives rise to an extrapolation length of the order of a few microns, which corresponds to weak anchoring.