Surface-Induced Parallel Alignment of Liquid Crystals by Linearly Polymerized Photopolymers

Abstract

Photopolymerization of polymer-coated solid substrates with linearly polarized light is shown to induce an anisotropic, uniaxial orientation of polymer molecules. The linearly photopolymerized (LPP) layers exhibit UV dichroism and optical anisotropy. The resulting anisotropic dispersive surface interaction forces are shown to align adjacent liquid crystals parallel. A qualitative microscopic model is presented. The new LPP-alignment technique allows to generate homogeneous LC-director pattern with different azimuthal director angles on the same substrate requiring no mechanical treatment. The use of LPP substrates in liquid crystal displays (LCDs) is shown to enable to combine different electrooptical effects-such as twisted nematic (TN) and parallel configurations-in the same hybrid LCD. Besides from high-contrast LPP-aligned TN-LCDs, LPP-aligned supertwisted nematic (STN)-LCDs exhibiting steep transmission-voltage characteristics are presented.