Factors influencing flexoelectric polarization in liquid crystals

Abstract

The work experimentally investigated the factors affecting the formation and physical parameters of flexoelectric polarization in liquid crystals (LC) with nematic as well as smectic A- and C-phases. Factors such as the heating temperature of the sample, orientation effects near the nematic – isotropic state (N-I) phase transition, and the initial orientation of LC molecules were studied. The thickness of the studied layers is from 10 to 100 μm, the frequency of exposure is 1000 Hz. It was found that the flexosignal takes maximum value in homeotropically oriented samples in the nematic phase. When approaching the N-I phase transition, the magnitude of the flex signal increases, which is associated with an increase in the deviation angle of the director of the LC. As the dipole moment grows, the quadrupole moment also increases. This is due to the tendency of LC molecules to form dipole pairs with antiparallel orientation of electric moments. The estimate of the flexural value U1ω yielded (for example, for MBBA) with a planar orientation 3 times less than with a homeotropic one. The presence of the second harmonic U2ω is a consequence of the orientational instability of surface polarization. The rapid growth of U2ω is associated with an increase in the square of the director deviation angle .