| dc.description.abstract | The main research topics in this thesis include the following three parts. In the first part, the characteristics of dichroic dyes-doped nematic liquid crystals (DD-NLCs) and the maximum adjustable dynamic range of transmittance of DD-NLCs are discussed in detail. To achieve the absorption state, LCs with positive dielectric anisotropy (E7) doped with various concentrations of dichroic dyes (S428) are filled into LC cells with various thicknesses and/or various structures, such as homogeneous alignment (HA), twisted nematic (TN), and hybrid alignment (HB) LC cells. Based on the influences of LC arrangement, LC layer thickness, and concentration of the doped dyes on the changes of transmittance, the absorption coefficients (A_⊥ and A_∥) are determined by experimental results and 1D-DIMOS simulation results. We found that the obtained absorption coefficients are consistent with the official absorption coefficients. Finally, to enhance the performance of adjustable dynamic range of transmittance, two LC cells with the same/different structures are tandem overlapped. It should be noted that the two DD-NLC cells with the required arrangement that the LC director close to the last layer of the first DD-NLC cell should be perpendicular to that close to the first layer of the second DD-NLC cell.
The second part in this thesis is the study of the characteristics of dichroic dyes-doped cholesteric liquid crystals (DD-CLCs) with long pitch lengths. According to the results of the first part, dyes-doped TNLC cell has the largest adjustable dynamic range of transmittance. Therefore, the effect of twisted angles of dyes-doped TNLCs will be examined here. To achieve the dyes-doped TNLCs with various twisted angles, LCs (E7) mixed with dichroic dyes (S428) and chiral dopant (S811) are filled into empty LC cells, whose substrates are coated with orthogonal homogeneous alignment films with mechanical rubbing process. For the purpose of finding the influences of twisted angle onto the changes of transmittance, we adjust the concentrations of the doped chiral dopant to fabricate LC cells with twisted angles of 180°, 360°, 540° and 720°. Finally, we compare the experimental results with the 1D-DIMOS simulation results to verify the effect of twisted angles.
The third part in this thesis is the study of the characteristics of multi-dichroic dyes-doped nematic LC. As is well known, the higher the dichroic ratio of dichroic dyes, the wider the adjustable dynamic range of transmittance. Therefore, we chose the three kinds of dichroic dyes, including AB4, AZO1 and AC1, whose dichroic ratios are 12.1, 11.8, and 13.6, respectively. Next, multi-dichroic dyes (AB4, AZO1, and AC1) -doped LCs with positive dielectric anisotropy (E7) are filled into LC cells with various thicknesses, whose substrates are coated with homogeneous alignment films with mechanical rubbing process. Based on the influences of LC arrangement, LC layer thickness, and concentration of the doped dyes on the changes of transmittance, the absorption coefficients (A_⊥ and A_∥) are determined by experimental results and 1D-DIMOS simulation results. Finally, we compare the dichroic ratio of multi-dichroic dyes to that of dichroic dyes (S428). | en_US |