Two beam coupling ratio and response time of photorefractive liquid crystal cell with SWNT-dispersed PVK layers

Abstract

The soluble SWNT in solvent and water was obtained from SWNT, purified and functionalized with forming carboxylic acids, and the dispersion was successfully monitored in optical observation, ξ-potential and SANS experiment. The dispersion in water forms an aggregated structure, but not in organic solvent. The SWNT solution was spin-coated on ITO glasses, and the films were assembled for liquid crystal cell, and the liquid crystal cell showed a good alignment of liquid crystals with SWNT layers. The photorefractive effect of liquid crystal cell fabricated with SWNT-dispersed PVK layers was investigated in two beam coupling ratio and response time. Two methods of SWNT-dispersed PVK layer were used to obtain the uniform dispersion. The one uses the blending of PVK and the surface modified SWNT and the other uses the chemical grafting of polymer onto SWNT. The mixed SWNT-PVK films were used for the photorefractive liquid crystal cells, which contain $C_{60}$, photosensitizer in liquid crystal. The Raman-Nath pattern and two beam coupling ratio were observed indicating the photorefractivity of liquid crystal cells, and the two beam coupling ratio of cell with SWNT was greater than those without SWNT. The response time of the cell with PVK grafted with SWNT was reduced than those without SWNT. The mechanism of the increasing two beam coupling ratio and reduced response time may not be clearly explained but SWNT plays a key role for the charge-trapping and transport.