Surface-assisted photoalignment control of lyotropic liquid crystals. Part 1. Characterisation and photoalignment of aqueous solutions of a water-soluble dye as lyotropic liquid crystals

Abstract

The surface-mediated alignment control of a lyotropic liquid crystal (LLC) of aqueous solutions of a water-soluble dye, C. I. Direct blue 67, by using thin films of poly(4-phenylazophenyl methacrylate) as a command surface is described. Concentrated aqueous solutions of the dye in the presence of a non-ionic surfactant displayed mesophases as a chromonic LLC as a result of stacking of the aromatic ring systems leading to a columnar structure. A uniaxially oriented texture of LLC was obtained when the LLC, in the presence of a non-ionic surfactant was filled in a cell, which had been exposed in advance to linearly polarised light and was surface-modified with thin films of the polymer. The orientational direction of the dye molecules was in parallel with the electric vector of the actinic light, implying that the alignment of LLC is determined by perpendicularly photooriented azobenzene chromophores in such a way that columnar supramolecular aggregates of the dye align in parallel with the azobenzene molecular axis. Factors affecting the photoalignment control of the LLC were discussed on the basis of the results of the effects of exposure doses, excitation wavelength and photo-rewritability.