Properties of Bulk-Mediated Photoalignment of Doped Liquid Crystal

Abstract

We have found that producing a light-induced easy axis in a liquid crystal cell doped with methyl red can result in surface director reorientation both toward and outward the polarization of the incident light. This pointed out two different mechanisms of light-induced anchoring in the system. We proposed that these mechanisms are light-induced anisotropy in the adsorbed MR-layer and light-induced adsorption of MR molecules on the substrate. The study of light-induced anchoring in the isotropic phase showed that the mechanism of light-induced anisotropy in adsorbed MR-layer prevails at small light intensities, whereas the mechanisms of light-induced adsorption dominates at high intensities.

Light-induced adsorption and desorption in Methyl-Red-doped liquid crystals: a review

“…Both papers showed that irradiation in the isotropic phase results in an anisotropic distribution of the adsorbed dye molecules in the LC phase, the effect being hidden when the material is in the isotropic phase. The induced easy axis could be either parallel and perpendicular to the polarization of the incident light, depending on light intensity [14] or, more precisely, on the light dose [15]. This behaviour was explained by two mechanisms: light-induced adsorption of MR molecules on the irradiated surface (already discussed) and (this is the novelty)…”

“…Several papers dated 2001 predicted the formation of a layer of MR molecules adsorbed on the cell inner substrates before cell irradiation [14][15][16][17]. Papers [14] and [15] describe the director reorientation due to cell irradiation in the isotropic phase.…”

“…Papers [14] and [15] describe the director reorientation due to cell irradiation in the isotropic phase. In order to reduce the variable parameter affecting the light-induced easy axis (dependent on the polarization direction and on the direction along which dye molecules adsorb on the surface which in turn depends not only on light polarization but also on the orientation of the director on the surface) the system was investigated in the isotropic state.…”

Surface microrelief obtained by composed target deposition for LC molecules alignment

“…In present LCD production a lot of techniques for creation of the planar or tilted homogeneous alignment of liquid crystal molecules (e.g., vacuum thermal deposition or electron beam evaporation of oxides, rubbing of the polymer films, photoalignment, plasma treatment and others [1][2][3][4][5][6]) are used. But these technologies have many imperfections.…”