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Variable liquid crystal pretilt angles by nanostructured surfaces and their applications

Authors Yeung, Fion Sze Yan
Issue Date 2007
Summary Liquid crystal displays (LCDs) are conventionally aligned by rubbing of a polyimide (PI) layer. Pretilt angles of 0°–10° are usually obtained for homogeneous alignment polyimide. Vertical alignment polyimide can give a pretilt angle of 85°–90°. However, there is much demand for an alignment layer that can produce intermediate high pretilt angles in the range of 30°–60°. Many applications can be made possible if such large pretilt angles are available. Traditionally, the best method of obtaining large pretilt angles is by SiO2 evaporation. However, this technique is not amenable to mass production and for large display panels. There have been other proposed methods including photoalignment technology, special polymer blends and block copolymers as the alignment layer. But none of them has proven useful so far. We have recently described a nanostructured alignment surface based on a random distribution of vertical and horizontal polyimide domains. In this thesis, we report results on these nanostructured surfaces to prove their usefulness in making novel liquid crystal displays. In particular, as the alignment layer for LCD, we show that such surfaces can indeed provide any pretilt angles between 0° and 90°. The polar anchoring energy of such surfaces is also very strong, being comparable to ordinary rubbed polyimides. In fact, ordinary polyimides are employed as the main ingredient in making such nanostructured surfaces. With these alignment layers, no-bias voltage π cells and several bistable displays have been successfully fabricated.
Note Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2007
Language English
Format Thesis
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