Phase separation induced polar electrooptical effect in a doped nematic liquid crystal cell

A cell prepared for vertical alignment was filled with a mixture of the liquid crystal octylcyano biphenyl, doped with a three-legged molecule, in the isotropic phase in the presence of an imposed temperature gradient perpendicular to the substrates. After cooling the cell through the nematic phase and restoring the temperature uniformity, an electrooptic response was observed on applying an electric field across the cell in one direction but not in the other. This unipolar effect was absent for cells prepared in the absence of a temperature gradient. The results are discussed in terms of phase separation and preferential adsorption of the tripod molecule.