Determination of azimuthal anchoring energy in grating-aligned twisted nematic liquid-crystal layers

In this work sinusoidal diffraction gratings with a range of pitches and amplitudes are used to align nematic liquid-crystal layers in a twisted homogeneous configuration. The grating profiles are accurately characterized using optical surface plasmon polariton spectroscopy, which then allows a calculation of the anchoring energy as predicted by the simple Berreman expression. The experimental Rapini-Papoular anchoring energy is also obtained by a measurement of the director twist away from the alignment direction (easy axis) at room temperature. A linear relationship is found between the two anchoring energies, except when it falls below 4 x 10(-7) J m(-2). Noticeably, the correlation between the two theories is not unity, if room-temperature elastic constants are used in the calculation. This apparent inconsistency is explained if the effect of surface memory on the system is considered Indeed, if elastic constants, corresponding to a higher temperature at which surface memory effects are absent, are used in the Berreman expression, good agreement between the predicted and experimentally measured energies is found. (C) 1997 American Institute of Physics.