dc.description.abstract | The research topics in this thesis include the following two sections. The first section focuses on the applications of the liquid crystal (LC) waveguide effect to discuss the fabrications of twisted hybrid polymer network LC (TH-PNLC) structures. When an edge light source is fed into the LC cell and no electric field is applied to the TH-PNLC cell, the refractive indices of the nematic LCs and the LC polymer are matched. As a result, the incident light undergoes total internal reflection within the LC cell. However, when an electric field is applied to the TH-PNLC cell, the refractive indices of the nematic LCs and the LC polymer become mismatched. This mismatch causes the incident light to scatter and emit from the two observation surfaces of the LC cell. When observing the scattered light emitted from the two surfaces, there is a difference in the main polarization components of the scattered light from the two substrates. Additionally, if the material is doped with a photoinitiator, this difference in polarization components will increase. To understand this phenomenon, we investigate the changes in the TH structures after photopolymerization and the variations in the polarization states of the scattered light from the TH-PNLC cell without doping and with doping of the photoinitiator in the material. Input unpolarized and linearly polarized light to TH-PNLC cells without doping and with doping of the photoinitiator, respectively, the different results of feeding side light sources into the two LC cells are obtained. In summary, the obtained results explain the reasons for the polarization differences in the scattered light emitted from the sides of the TH-PNLC when unpolarized light is incident from the side. Finally, the asymmetric scattering property of the TH-PNLC structure is utilized to demonstrate unidirectional LC light source devices and privacy protection applications.
In the second section, negative-type LCs doped with chiral dopants and ions are used to demonstrate an LC cell fabricated by two ITO glass substrates coated with a PVK film and a vertically aligned film. By utilizing the PVK film′s ability to block DC electric fields and its property of forming a good conductor when exposed to ultraviolet light, it is possible to obtain pattern addressing work using dynamic scattering of LCs. When a suitable high-frequency electric field is applied to the LC cell, it can be switched to a transparent state with planar textures. Even after the external electric field is turned off, it can still maintain the transparent state with imperfect planar textures. However, by applying a low-frequency or DC electric field, the transparent state can be switched to a scattering state with focal conic textures via dynamic scattering. Similarly, even after the external applied electric field is turned off, it can maintain the scattering state (focal conic textures). Due to the characteristics of the PVK film, the LC cell can be divided into two regions exposed to ultraviolet light using a photomask. When a DC electric field and ultraviolet light are applied simultaneously, the LC cell can exhibit a scattering state for text patterns and transparent regions for the rest. When an edge light source is fed into the LC cell with the addressed pattern, the principle of the LC waveguide is utilized to display the contrast. Incident light in the transparent region undergoes total internal reflection due to the continuous refractive index, resulting in no light being emitted from the side view. However, in the scattering region with the addressed pattern, the discontinuous refractive index causes the patterns to emit light, thereby enhancing the overall contrast of the LC cell. | en_US |