Daisaku Matsunaga

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

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.

Azo-pendant polyamides which have the potential to photoalign chromonic lyotropic liquid crystals

A new series of polyamides (ph-azo-PAMs) was synthesized by the polycondensation of isophthalic acids having a photoisomerizable phenyl azo unit with 4,4′-diamino-3,5,3′,5′-tetraethyldiphenylmethane or by the esterification of poly(imino-5-oxyisophthaloylimino-1,4-(3,5-diethyl)phenylenemethylene-1,4-(3,5-diethyl)phenylene) with 4-(phenylazo)- or 4-(4′-substituted phenylazo)phenoxyalkanoic acid chlorides in the presence of triphenyl phosphate and pyridine in N-methylpyrrolidone. It has been confirmed that the spin-coated films of ph-azo-PAMs thus produced show reversible trans–cis photoisomerization of the azobenzene moieties. To examine the ability of the polymer films to act as command surfaces for a chromonic lyotropic liquid crystal (LLC), they were exposed to linearly polarized light and coated with aqueous LLC solutions of a chromonic dye compound. After drying the LLC solution, polarizing microscopic measurements were carried out to see whether the phototreated polymer films could bring about the in-plane anisotropic alignment of the dye molecule. The result was that 5h having an azo moiety with a dimethylamino substituent as a side group was among the most promising candidates.