Unusual Ionic Effects in Liquid Crystal Materials

Display and non-display applications of thermotropic liquid crystals rely on the reorientation of liquid crystal molecules by the applied electric field. This reorientation can be affected by ions typically present in liquid crystals in small quantities (in the simplest case, through a well-known screening effect when the electric field due to the ions can cancel out the applied electric field). Therefore, an understanding of ion-related effects in liquid crystals is critical for the development of advanced liquid crystal devices. Important information about ions in thermotropic liquid crystals can be obtained by measuring their DC electrical conductivity. An interpretation of the DC electrical conductivity data requires reasonable approximations. As a rule, a single type of dominant ions or two symmetric ions of the same mobility are assumed. In this presentation, the effects of several types of ions (characterized by different values of their mobility) on the measured DC electrical conductivity of liquid crystals are discussed. The substrates of the liquid crystal cell and their important role in the ionic processes is also considered.