Aligning Mechanism and Electro-Optical Responses of the Uniform Lying Helix State Based on the Flexoelectric and Dielectric Effects

• Main Authors: Lin, Yueh-Chern, 林岳辰
• Other Authors: Lee, Wei
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/jmq47p

碩士 === 國立交通大學 === 照明與能源光電研究所 === 107 === In this study, we attempt to promote the strength of the flexoelectric response by incorporating a proper amount of bent-core liquid crystal (LC) dimer CB7CB into rod-like cholesteric liquid crystal (CLC) with positive dielectric anisotropy, and investigate the voltage-dependence of electro-optical responses and the formation of various textures. With suitable voltages, we evidence that defect-free uniform lying helix (ULH) can be obtained, based on the dielectric and strong flexoelectric effects, under the frequency f conditions of f < fULH. For frequencies in the regime between fULH and fFC, the strength of the flexoelectric effect get decreased with rising frequency and the coexistence of both focal conic (FC) and ULH is generated, whereas for the cell treated with the voltage at f > fFC, the flexoelectric effect almost disappears completely and the resulting texture is FC. Attractively, when placing the ULH cell between crossed polarizers, with the helical axis being parallel to the transmission axis of either linear polarizer, our study demonstrates that the light intensity can be controlled without phase change by adjusting the frequency of AC voltage at a fix amplitude. This indicates that the strength of the flexoelectric effect can be modified by the frequency, but in the meantime the dielectric effect is nearly invariant. In consequence, CB7CB-doped CLC in the ULH state exhibits considerable and frequency-dependent flexoelectro-optical responses which can scarcely be acquired in typical rod-like CLCs, thus this study promotes a giant potentiality for practical application of ULH for fast-response LC devices.