Fatih Akkurt

Phase Transitions, Order Parameters and Threshold Voltages in Liquid Crystal Systems Doped with Disperse Orange Dye and Carbon Nanoparticles

At the first part of this work, three different textile dyes (disperse orange 11, 13 and 37) were separately doped (1% w/w) to the nematic liquid crystal (E7). Single‐walled nanotube and fullerene C60 in a small amount (0.05% w/w) were mixed to these solutions at the second stage. Order parameters, threshold voltages, textures and clearing temperatures for all of mixtures were determined. Co‐use of dyes and nanoparticles as dopant was resulted in notable increases in order parameters. While threshold voltages required for the change of order parameter decreased, an important change in the texture and clearing temperature of the liquid crystal was not observed.

Characterisation of azo dye and carbon nanoparticle-doped guest–host liquid crystalline matrix

During the recent years, liquid crystals (LCs) have much attention owing to their wide range of possible application and structural properties in electronics and optics. In this study, two different azo structured dyes (Disperse Yellow 3 and 7) and their mixture were separately doped to each of two different nematic LCs (E8 and E63). Their solubilities (except dye mixture), order parameters, textures and phase transition temperatures were determined. Single-walled nanotubes and fullerene C60 in a small amount were separately added to each of these solutions, and the experiments were repeated at the final stage analogously except solubilities. The solubilities of dyes in the LC E63 were lower than those of E8. The highest order parameter value was attained with Yellow 7 dye in E63 nematic host.

Alignment and Reorientation in Nematic Liquid Crystals Doped with Red Dye and Carbon Nanotube

Four different dyes (Methyl red, Disperse red 1, 13 and 60) were separately doped to each of four different nematic liquid crystals (E7, E8, E63 and ZLI-1132). Their solubilities, textures, phase transition temperatures and order parameters were determined. At the second stage, single-walled nanotubes in a small amount were separately added to each of these solutions, and the experiments were repeated as similar to previous ones. The solubility of dyes was sufficient for using in experiments. When adding dyes and nanotubes, an appreciable change in textures of liquid crystals was not observed. The phase transition temperatures stayed within the limitations required. The changes observed in order parameters depending on the voltage were very small. The highest value of order parameter (0.77) was attained when co-using red 60 dye and nanotube as dopants in the liquid crystal E63.

Orientation in Nematic Liquid Crystals Doped with Orange Dyes and Effect of Carbon Nanoparticles

Some properties of nematic liquid crystal E7 doped with two disperse orange dyes used together and effect of addition of carbon nanoparticles (single walled carbon nanotube or fullerene C60) on them were studied. Two dyes (disperse orange 11 and 13) having high solubility and order parameter were used as co-dopants. A notable increase in order parameter was obtained comparing to that of liquid crystal doped with single dye. When carbon nanoparticles were used as dopant, a decrease in order parameter was observed at low temperatures while it increased at high temperatures. When applied voltage changed, the order parameter abruptly increased in its threshold value and saturated in higher voltages as expected. An appreciable change in textures was not observed with addition of dopants. This addition gave rise to an increase in nematic-isotropic phase transition temperatures compared with that of pure liquid crystal.

Effects on molecular orientation and phase transition of addition of carbon nanotubes into liquid crystalline matrix

For practical guest–host applications, it is important to choose dyes with a high ability of orientation in the liquid crystal (LC) matrix. In this experimental work, two different azo-structured dyes (disperse yellow 3 and 7) were separately doped to each of two different nematic LCs (E7 and ZLI-1132). Their solubilities, textures, phase transition temperatures and order parameters were determined. At the second stage, single-walled carbon nanotubes (SWCNTs) in a small amount were separately added to each of these solutions, and the experiments were repeated as similar to the previous ones. The solubilities of dyes in the LC E7 were lower than those of ZLI-1132. Moreover, the highest order parameter value was attained with yellow 7 dye in ZLI-1132 nematic host. Co-use of nanoparticles (CNTs) as dopant resulted in notable increases in order parameters. These dyes and CNTs did not significantly destabilise the mesomorphic phase of nematic hosts. An appreciable change in textures was not monitored with addition of dopant(s). In addition, it was observed that the narrowing on the temperature range of the LC did not take place with the addition of dopants to the crystal; on the contrary, an increase was recorded.

Phase Transitions and Molecular Orientation in Nematic Liquid Crystals Doped with Blue-red Dye Mixtures and Carbon Nanotubes

Phase transitions and molecular orientation in nematic liquid crystals (E7, E8, E63 and ZLI-1132) doped with blue dye (disperse blue 1, 3, 14 or 134) and blue 14 + red dye (disperse red 1, 60 or methyl red) mixtures were studied. At the second stage, effects of single-walled carbon nanotubes (SWCNTs) added to them were determined. When blue-red dye mixtures were doped into the liquid crystals, an increase in order parameter was observed compared to those of single dyes and a value of 0.70 was attained. The addition of carbon nanotubes resulted in very higher values of order parameter (Smax = 0.79). To determine the threshold value of order parameter for saturation, the experiments were repeated in various DC voltages. The threshold voltage was significantly reduced with addition of CNTs. With addition of dopants, an appreciable change in textures was not observed. Shifts in phase transition temperatures were in limitations required.