Investigation on Electric-optical characteristics of optical-isotropic liquid-crystal devices

• Main Authors: Ji-Yi Chiou, 邱繼毅
• Other Authors: Hui-Yu Chen
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/48059665305945950200

碩士 === 逢甲大學 === 光電研究所 === 99 === This thesis focuses on studying the electro-optical effects in four optical isotropic phases: (1)Blue phase; (2)Polymer stabilized blue phase; (3)Polymer stabilized isotropic phase; (4) Polymer stabilized isotropic phase with random double twist cylinder. Two electric-field induced phenomena of the blue phase are observed in this thesis: 1) a shift in reflection band at a low electric field because of director reorientation and 2) a phase transition from blue phase to chiral nematic with focal conic texture at a high electric field. The slight wavelength shifts of the reflection spectrum are attributed to the electrostriction effect (or lattice distortion) caused by reorientation of the liquid-crystal molecules. It is important to note that blue phase exhibits a local dielectric anisotropy inside the double twist cylinder. When the strength of the electric field increases continuously, the phenomenon of movement or rearrangement of disclinations occurs in the blue phase. Although the range of shift in the reflected wavelength can be extended, the intensity of the selective reflection decreases. Some lattices of the blue phase breaks under the strong electric field, and then the blue phase begins the transition to chiral nemtaic . In polymer-stabilized blue phase, the electro-optic effects are similar with ones in blue phase. The response time of phase transition relates with chirality, dielectric anisotropy, elastic constants and rotational viscosity of the liquid crystals. According to experimental results in polymer stabilized isotropic phases, two different structures of them can be distinguished. One of them only can be driven by an in-plane electric field. The other structure, which is constructed by random double twist cylinder, can work either in a vertical electric field or in an in-plane electric field.