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Category International Presentation
Paper Title Control of Liquid Crystal Pretilt by Thermally Assisted-Transfer of Siloxane Oligomers during Contact Printing
Conference name International Liquid Crystal Conference 2014
Author Jeng-Hun Suh, Jiyoon Kim, Sin-Doo Lee
Paper code Place
page Year/date 2014/07/03
Abstract The surface alignment of liquid crystals (LCs) has been extensively studied for understanding the interfacial interactions of the LC molecules and for designing a variety of electro-optic (EO) devices. In the LC alignment, besides the surface anchoring energy, one important parameter is the pretilt angle of the LC at a substrate surface which enables to construct multi-domains of the LC and to enhance the EO properties required for specific applications. Previously, a number of the approaches to the control of the pretilt angle, for example, different aligning materials by rubbing, dual alignment layers, the modification by ultra-violet irradiation, the use of an polydimethylsiloxane (PDMS)-based alignment layer, have been suggested. However, none of them produce a relatively wide range of the pretilt angle varying ideally from 0°to 90° in a continuous manner.
In this work, we demonstrate a simple and powerful technique for controlling the pretilt angle of the LC in a wide range by the thermally assisted-transfer of siloxane oligomers onto a substrate. For the modification of the surface energy which dictates the pretilt angle of the LC, PDMS oligomers were thermally transferred onto the substrate from a PDMS mold during contact printing. It was found that the amount of the transferred PDMS oligomers, which tends to reduce the surface energy of the substrate, increases with the temperature during contact printing and the resultant pretilt angle increases monotonically from about 0° to 89°. The uniformity of the LC alignment will depend on the uniformity in the surface coverage of the transferred PDMS oligomers on the substrate.

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