Photosensitive Polymer from Ionic Self-Assembly of Azobenzene Dye and Poly(ionic liquid) and Its Alignment Characteristic toward Liquid Crystal Molecules

A new strategy based on ionic self-assembly technology was provided for design of photosensitive material as liquid crystals (LC) alignment layer. The complex material was constructed by the coupling of poly(ionic liquid) and photosensitive unit azobenzene dye methyl orange. The structure, phase behavior and photoresponse were examined by a variety of techniques including FTIR, NMR, thermal analysis, polarized optical microscopy, X-ray diffraction, small-angle X-ray scattering, and birefringence measurements. Highly ordered lamellar nanostructure and photosensitive character were confirmed. Under the irradiation of pulsed UV laser with certain fluences, a pronounced optical anisotropic surface with the preferred direction perpendicular to the pulsed polarization or regular periodic grooves microstructure surface parallel to the pulsed polarization was obtained. The anisotropic surface of oriented molecular chain or topography was demonstrated to result in the alignment of LC by the optical transmittance plot and polarizing microscopy images of LC cells with different rotation angles.