| dc.description.abstract | This thesis reports on the optical properties of uniform lying helix (ULH) structures generated by the application of electric fields with different frequencies and by doping liquid crystal (LC) dimers into cholesteric LCs (CLCs), the structure is used to enhance forward scattering (light scattering towards the photodetector) and reduce backward scattering (light scattering towards the observer), thereby enhancing display contrast. The thesis is divided into two parts, with the primary objective of analyzing and optimizing the CLC structures for applications in electronic papers of reflective mode displays to enhance contrast and performance.
In the first part of the experiment, the properties of undoped and CB7CB-doped CLCs filled into LC cells with different cell gaps were studied. First, the overall transmittance decreases with the increase of cell gap, such as from 3.22 μm to 5.25 μm. The influences of the LC cell gap on the electro-optical properties of CLCs without doped LC dimers significantly affect display performance. Additionally, the performance of CB7CB-doped CLCs with three different reflective light spectra (RGB) was analyzed in detail. With appropriate voltage and frequency control, focal conic (FC) structures with a transmittance of approximately 53% and ULH structures with a transmittance of approximately 82% can be achieved. These structures demonstrated significant advantages in enhancing forward scattering (the best improvement of roughly 29%) from the CLC structures. The differences in overall transmittance and structural properties were also examined using CB7CB-doped CLC with different helical pitches, such as 399 nm,335 nm, and 267 nm).
The second part of the experiment delved into the impacts of doping LC dimers on the optoelectrical properties of CLCs. First, the effect of doping LC dimers on the response time of CLCs was analyzed. The response times of LCs applied with electric fields with direct current or low-frequency alternating current were measured. The experimental results indicated that doping CB7CB effectively shortens the response time by approximately 8 seconds compared to the undoped CB7C. Moreover, at suitable frequencies and electric fields, a smaller pitch length significantly enhanced the reduction in response time, with the shortest response time being approximately within one second. Additionally, experimental findings revealed a slight enhancement in grayscale display effectiveness with CB7CB. Optimal grayscale modulation was observed under suitable d/p ratios (d/p = 12, d represents the LC cell gap, and p represents the pitch), applied voltages, and frequency conditions. The transmittance shows the highest linearity, with the greatest difference between the highest transmittance (82%) and the lowest transmittance (53%), resulting in better grayscale control (voltage-transmittance curve is close to a oblique straight line). Furthermore, the study also explored whether doping ion materials (SDS) could enhance dynamic scattering and reduce response time. The impact of another LC dimer, CB11CB, doped into CLCs was also examined. Unfortunately, the experimental results showed that the ULH structures cannot be generated using these methods. | en_US |