All-optical manipulation of cholestric liquid crystal micromotor using technique of optical tweezers

• Main Authors: Cheng-yenYu, 余承諺
• Other Authors: Chia-Rong Lee
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/73097036784287128897

碩士 === 國立成功大學 === 光電科學與工程學系 === 101 === This thesis aims to develop an all-optically controllable micromotors based on cholesteric liquid crystal (CLC) microdroplets added with a chiral azobenzenze. The CLC microdroplet shows an axial structure of helical axis with a ring-defect on the equator of the microdroplet such that the circularly polarized red beam of the optical tweezer may transfer its angular momentum to the microdroplet and then induce rotation motion. The irradiations of one UV beam and the beam of the optical tweezer may control reversibly the ability of rotation of the CLC micromotor. The investigations in the thesis include two parts. In first part, we study the dependence of the rotational ability of the CLC micromotor manipulated by the red beam of the optical tweezer (wavelength: 660 nm, power: 100 mW) on the pitch and the diameter of the CLC microdroplet under the . In second part, a chiral azobenzene is added into the CLC microdroplet for studying the optical controllability of the micromotor. When the chiral azobenzene added CLC micromotor is irradiated by a weak UV beam (intensity: 21  82 mW/cm2), the chiral azobenzene molecules may change from rod-like trans isomers to curve cis ones, which may locally disturb the LC order and thus gradually decay the rotational ability of the CLC micromotor. Once the intensity of the UV irradiation increases up to 109.4mW/cm2, a large number of cis chiral azobenzene may rapidly generate to seriously disturb the microdroplet, which may quickly stop the rotation of the microsphere. The successive irradiation of the red beam of the optical tweezer following the UV irradiation may induce cistrans back isomerization of the chiral azobenzene, which may induce the recovery of the ordered CLC structure in the microdroplet and thus the restoration of the rotational ability of the micromotor. Therefore, the use of the irradiation of weak or strong UV light in controlling the rotational ability of the CLC microsphere under the manipulation of the optical tweezer is applicable to the development of the all-optically tunable or switchable micromotor.