Investigation of characterization and applicability of nematic liquid crystals doped with blue - red dyes and carbon nanotubes

Especially with applications of the display technology in recent years, liquid crystals have become the focus of great interest. Guest-host liquid crystal displays (GH-LCDs) have attracted much attention because of their wide viewing angle, lower costs, excellent hues and high brightness levels. For G-H applications, it is very important to choose dyes with a high ability of orientation in the liquid crystal matrix.The aim of this Ph.D. dissertation is to improve the molecular orientation in the GH-LCDs with single dyes, their binary mixtures and carbon nanotubes to examine the influence on the nematic-isotropic phase transition temperature of the pure hosts. Firstly, eight different dyes (methyl red, disperse red 1, 13, 60 and disperse blue 1, 3, 14, 134) were separately doped to each of four different nematic liquid crystals (E7, E8, E63 and ZLI-1132). Their solubilities, textures, phase transition temperatures, order parameters and its change with applied voltage were determined. At the second stage, single-walled carbon nanotubes in a small amount were separately added to each of these solutions and the experiments except solubilities were repeated as similar to previous ones. Finally experimental studies were completed by using couple of dyes.It can be said that as a result; the solubility of dyes at room temperature was appropriate for a good contrast ratio except disperse blue 1 dye. When using a couple of dyes in nematic matrice, a notable increase in value of order parameter was observed by comparing to the results obtained with single dye. The order parameters increased remarkably by addition of nanotubes. When adding dyes and nanotubes, an appreciable change in textures of liquid crystals was not observed. The evaluation of polarizing microscope and DSC results showed that the phase transition temperatures stayed within the limitations required, except liquid crystals doped with disperse blue 134 dye. The changes observed in order parameters depending on the voltage were in very small size and it saturated in higher voltages. Order parameters remained constant for mixtures containing disperse blue 1 and 3 dyes although changes in DC voltage. The threshold voltage for saturation was significantly reduced in the presence of a small amount of CNT.