The surface of multilayered opal crystals resulted in homeotropic alignment of liquid crystal (LC), originated from the surface topography of opal crystals rather than a chemical nature of the nanoparticles. The polar anchoring energy (5.51 × 10 J/m) of the crystal surface for nematic LC molecules was in a similar range to the conventional polyimide alignment layer (2.11 × 10 J/m) used for commercial applications. The critical length scale for anchoring transition was approximately Lw = ~1 μm. If a diameter of particle d << 1 μm for opal crystals, LC molecules preferred to anchor vertically to the surface to minimize elastic free energy of bulk LCs. The LC favored a planar anchoring if d >> 1 μm. The results provide crucial insights to understand the homeotropic alignment of LCs on solid surfaces and therefore offer opportunities to develop novel materials for a vertical alignment of LCs.
Photo-reactive self-assembled monolayer (PR-SAM) is employed to mediate alignment of liquid crystals (LC) and stabilize the tilt orientation of a nematic director for a vertically aligned liquid crystal. Bifunctional PR-SAM formed by silane coupling reaction to oxide surfaces efficiently induces a homeotropic alignment and stabilizes LC director by the photo-polymerization under applied electric field. As a result, the substantial enhancement of electro-optic performance has been achieved after the PR-SAM assisted stabilization of tilt orientation of director. This approach for pretilt stabilization has multifarious advantages over the conventional PSVA.
The surface monolayer stabilized vertically aligned liquid crystal (VA‐LC) mode is presented for television applications. Photo‐reactive self‐assembled monolayer (PR‐SAM) is formed on inorganic oxide surfaces. The SAM layer on oxide surfaces initially induce a homeotropic alignment of nematic LCs. Subsequent polymerization of the photo‐reactive SAM under applied electric field efficiently stabilizes LC alignment and induces a stable pretilt of LC molecules for four different directions in each pixel of the fishbone‐patterned VA‐cells. As results, improved electro‐optic characteristics, such as faster grey‐to‐grey response time, lower threshold voltage and enhanced brightness, are obtained after the polymerization‐induced stabilization of the photo‐reactive SAM.
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