Surface-mediated light-controlled Friedericksz transition in a nematic liquid crystal cell

Abstract

Surface-mediated director reorientation in a pure nematic liquid crystal (LC) cell in the presence of both a dc and low-power optical field has been observed. A surface-dependent lowering of the Friedericksz transition voltage in a planar cell upon light irradiation was found. It is believed that this effect is due to a light-induced change in the near-surface ion concentration in the presence of a dc field and a photosensitive surface. Enrichment in the ion concentration near the surface causes a redistribution of the electric field in the cell and its localization near the surface. As a consequence, the energy of interaction between the LC and the dc field near the surface overcomes the anchoring energy and results in the director reorientation.

Adsorption–desorption phenomenon and the kinetic equation at interfaces in liquid crystalline systems

“…Let r(z, t) be the density of impurities in the dielectric liquid. In practical cases, r(z, t) can represent the density of a dye dissolved in the liquid crystal sample [6][7][8][9][10][11][12][13][14][15], or the density of ions resulting from molecular dissociation (intrinsic) or from the dissociation of impurities present in the liquid. Consider that on r acts an external force F52,U(z), where U(z) is the potential of F. In this case F is responsible for a net current which, in the limit of small |F|, is given by j F 5mrF, where m is the mobility and j F is the driftcurrent due to F. The total current is then…”

“…The main interest of this kind of research is connected with the possibility to modify the nematic orientation with light [6][7][8][9][10][11][12][13][14][15]. According to the experimental studies, the dye initially dissolved in the nematic liquid crystal is selectively adsorbed by the limiting surfaces, and oriented by the nematic field.…”

Surface-Mediated Beam Coupling in Nominally Pure Nematic Liquid Crystal

“…Photorefraction in liquid crystals has recently attracted significant attention since it is characterized with strong optical nonlinearities at low light intensities and voltage [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. Currently, liquid crystalline materials are considered a leading candidate for those applications that do not require long storage times.…”

Investigations of dynamic photorefractivity regime by optical polarizing microscopy

“…The optical anisotropy is characterized by the value Dn = 0.152 (n e = 1.672 and n o = 1.520) at a wavelength of 632.8 nm. The possible surface−mediated "photosensitivity" mecha− nism is attributed to the adsorption/desorption of ions from the polymer aligning layers under light illumination at the applied external electric field [28]. The experiment was car− ried out at a temperature of 16-18°C.…”