Gvozdovskyy I. UV-induced effects in the nematic liquid crystals with dopants of the steroid biomolecules

In this thesis it has been found that the cholesteric phase is induced in the nematic liquid crystals (ZhK-805 and ZLI-1695) by steroid biomolecules (vitamin D isomers and relative compounds) as chiral dopants. It has been observed that dopants with rigid steroid skeleton (cholesterol, 7-dehydrocholesterol, lumisterol and ergosterol) possess lower helix twisting power (HTP) in contrast to steroid with flexible molecular structure of vitamin D (ergocalciferol). For the first time dynamic of the cholesteric phase induction was studied by observation the dissolution process of a steroid microcrystal of 0.1ё1mm length at the nematic droplet. Using a polarizing microscope, the new effect of rotation of a needle-shaped or prismoidal microcrystals was observed during dissolution in the nematic droplet and the correlation between the rotation direction and the sign of the induced cholesteric helix was observed. By simultaneous irradiation of provitamin D in ethanol and in the LC matrices (ZhK-805, ZLI-1695) with BUV-60 (or EL-30) lamp significant difference in the spectral kinetics has been revealed. Dramatic increase in the absorbance suggests that the trans-isomer tachysterol is formed more efficiently in the LC matrix. When the wedge-like LC cells with the cholesteric mixtures were irradiated with fluorescent lamp (EL-30), a progressive decrease in the Cano-Grandjean stripes number with exposure time was observed. This indicates that the chiral dopant undergoes phototransformation (hexadiene ring-opening) into a photoisomer possessing lesser HTP. Linear correlation between the decrease in the Cano stripes number and accumulation of previtamin D (in vitro) has been observed under simultaneous solar irradiation of the LC cell and the cuvette with ethanol solution of 7-DHC. By this means our findings hold promise for dosimetry of biologically active UV-B solar/artificial radiation (280ё315nm) by observation the Cano stripes number depending on the accumulated UV dose. The LCs photoalignment by thin films of the steroid biomolecules was examined. The photoalignment ability both of the provitamin D3-doped polymer film using polymethylmethacrylate (PMMA) and the monolayers of provitamin D3 adsorbed (or deposited by Langmuir-Blodgett techniques) at the substrate surfaces of a LC cell was studied in the thesis. Using provitamin D3 adsorbed films, a possibility of electrically controlled change in the LC orientation was studied. Transmission-Voltage characteristics of both non-irradiated (H orientation) and irradiated (P orientation) parts of the cell with nematic LCs were measured and reversible switching between the two orientations have been achieved by applied electric field (2ё4V) that is usable for high contrast of the pixels in the LC display technology.