Anchoring strength for twist deformation at a nematic liquid crystal-wall interface

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Abstract
We measured the twist rotation at the wall-nematic liquid crystal interface in MBBA and ZLI 1738 samples placed in a magnetic field giving a pure twist deformation. Homogeneous boundary conditions were obtained by rubbing two silane coated glasses softly with teflon. In the samples examined, a rotation angle of the order of 10° was obtained with a magnetic field of 5 kOe. This corresponds to an extrapolation length and an anchoring constant of the order of 1 μm and 0.005 dyn/cm respectively. Measurements were made by analysing the light transmitted through the samples. It is shown that in such experiments the adiabatic theorem cannot be considered valid, since even very small deviations from adiabaticity play a leading role in determining the intensity and the polarization state of the transmitted beam