Polar anchoring energy and tilt angle measured by magneto-optical technique in nematic doped with ionic surfactant

The surface anchoring of a nematic doped with the ionic surfactant has been investigated and compared with the one in the undoped sample. The director tilt angle at the substrates coated with the orienting polymer film has been determined by the null method in a rotating magnetic field. The Frederiks transition in a magnetic field has been chosen as a convenient technique to measure the polar anchoring energy W-theta. The temperature dependences of anchoring energy have been obtained for the various nematic cells. The W-theta values for nematic doped with the ionic surfactant are less than for the undoped one. The factors affecting the measurement accuracy have been discussed. The accuracy is higher for the thinner nematic layers and weaker anchoring energy.