报告内容简介

Part 1: Perfect helical planar state and fast switching time in Cholesteric liquid crystals enabled by liquid crystal dimer
Abstract: Cholesteric liquid crystals possess a self-assembled helical structure and exhibit unique selective reflection in visible and infrared light regions.  Their optical properties can be electrically tuned. The tuning involves the unwinding and restoring the helical structure. We carried out an experimental study on the mechanism of the restoration of the helical structure. We constructed cholesteric liquid crystals with variable elastic constants by doping bent-dimers and studied their impact on the restoration. With matched twist and bend elastic constants, the helical structure can be restored dramatically fast from the field-induced homeotropic state. Furthermore, defects can be eliminated to produce perfect planar state which exhibits high selective reflection.

Part 2: Selective scattering of PDLC film for light enhancement of OLED
Organic light emitting diode (OLEDs) is a new technology for flat panel display, which has the advantages of a flat thin profile, light weight and curve shape.  It power efficiency is, however, limited by total internal reflection within the OLED structure. Light produced within the organic layer is emitted in all directions. Only light emitted in directions near the normal (within 42o) of the display cell substrate comes out of the display, while light emitted in directions away from the normal is totally reflected back and wasted.  

We developed a novel light enhancing film for OLED display based on polymer dispersed liquid crystal (PDLC). In the film, the liquid crystal droplets are unidirectionally aligned along the film normal direction and exhibit selective scattering: it scatters light emitted only in directions with large incident angles, as shown by the red line in Fig. 1, but not light emitted in directions with small incident angles, as shown by the blue line in Fig. 1. When the light is scattered, it changes propagation direction and exits the OLED. The PDLC film reduces the total internal reflection and thus can significantly increase the light efficiency of the OLED. The angular profile of the emitted light intensity of an OLED without and with the PDLC enhance films are shown in Fig. 2.

报告人简介:

Chemical Physics Interdisciplinary Program, Liquid Crystal Institute,
Kent State University, Kent, Ohio 44242, USA,

杨登科（Yang Deng-Ke）教授于1984年在清华大学获得物理学学士学位，随后在夏威夷大学从事蓝相液晶的研究，并于1989年获得物理学博士学位，此后在肯特州立大学液晶研究
中心开展液晶领域的研究工作并任职，目前是液晶研究中心及化学物理系的终身教授。杨登科教授的主要研究方向为胆甾相液晶、液晶/聚合物复合材料及电光器件，是世界著名的液晶物理与器件方面的科学家，是高分子稳定液晶材料和双稳态液晶显示材料与器件的奠基者之一。杨登科教授已从事液晶科学与应用的研究近30年，是本领域内公认的具有影响力的学者，同时也是液晶显示相关企业所熟知的科学家，在国内外具有非常高的知名度。已发表学术论文190余篇，申请专利23项，著有专著3本，参与编写章节的专著5本，近十年独立申请项目近20项，与多家业内知名企业开展合作。参加 APS、SID和ILC等协会，并积极参与国际会议、国际交流等。2005年因其在聚合物稳定器件与反射型液晶显示领域的开创性工作获得SID的特殊贡献奖 ( Information Display Society Special Recognition Award )，2007年因其在双稳态、反射型胆甾相液晶显示、聚合物稳定液晶器件方面的科学与技术贡献及其对液晶科学和技术领域的教育所做出的突出贡献被聘为SID Fellow；其指导的学生论文也多次在重要的国际会议上获奖，例如，获得2011年液晶显示学会期刊年度优秀论文奖（Journal of the Society for Information Display Outstanding Student Paper of the Year Award 2011）、2012年SID国际会议优秀学生论文奖（Distinguished student paper of the 2012 SID International Symposium）。

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