Fabrication of Vertical Alignment Composite Film (VACOF) for Liquid Crystal Molecules by Ultra-Violet Light Induce Phase Separation Principle and Their Electro-Optical Characteristics

• Main Authors: Czung-Yu Ho, 何宗育
• Other Authors: Jiunn-Yih Lee
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/58sk67

博士 === 國立臺灣科技大學 === 材料科學與工程系 === 99 === In the study, we use non-contact photo-polymerization induced liquid crystal (LC) and pre-polymer to form a vertical alignment (VA) effect of pseudo-Polymer thin film after the phase separation. In the molecular structure design, we utilize photo-curable acrylic pre-polymer, (alkyl long carbon chain and main chain biphenol type etc.) and mix photo-initiator and negative dielectric anisotropy type liquid crystal (NLC) etc. component together. Forming the homogeneous LC mixture solution (NLC/photo-curable acrylic pre-polymer mixture systems) is via enough stirred and ultrasonic vibration. We use photo-polymerization induced phase separation (PIPS) effect, and to make the NLC and the photo-curable acrylic pre-polymer generate composite layer structure of the vertical alignment copolymer film (VACOF) after the Ultra-Violet (UV) light irradiation. The photo alignment of this novel technology can not only improve the traditional rubbing alignment shortcoming but also promote yield of the process. Our goal is expecting toward shortening the process for manufacture and decreasing the cost of the panel. This paper was mainly divided into three experimental systems. First of all, we discussed the photo-alignment mechanism for the negative-type LC/acrylic pre-polymers mixture systems and measured electro-optical characteristic of the LC device, such as the contrast ratio, transmittance, response time etc. of the LC molecules under variant carbon chain length of alkyl acrylic photo-alignment A. By the quantitative data such as threshold voltage (Vth), driving voltage (Von), saturation voltage (Vsat) and reaction time and so on, we could extrapolate the anchoring energy of VACOF surface in this systems, the photo-alignment mechanism of LC molecules and the interaction between the acrylic pre-polymers of different alkyl chain length and the LC molecules and so forth. Secondly, we analyzed and discussed the influence on VACOF surface micro-structure, LC device’s display conditions and electro-optical properties in the molecule structure of main chain bisphenol type acrylic pre-polymers B of different length and the LC cell of different thickness (2 μm, 4 μm and 6 μm). Finally, we expect to arrange overall LC molecules in a vertical alignment by mixing two chiral centres smectic A (SmA *) LC synthesized in our laboratory with photo-induced vertical alignment negative type LC/acrylic pre-polymer mixture systems. (SmA* LC resulted in a homeotropic texture under the POM with crossed polarizers). In addition, due to the SmA* LC exhibits the electrical field induced molecular tilt effect (electroclinic effect) and offers faster response time than ferroelectric LC, it has the characteristics of fast response and memory, and further allows for the gray-scale capability of adjusting the amount of light passing through etc. We hope to take advantage of the SmA* LC materials to improve electro-optical characteristics of the original system.