Photoalignment and patterning of a chromonic–silica nanohybrid on photocrosslinkable polymer thin films

Abstract

We recently found that the chromonic mesophase structure of an azo dye can be immobilized by a silica network to form a chromonic–silica nanohybrid. This work reports the first demonstration of the macroscopic photoalignment and photopatterning of this nanohybrid via surface-mediated orientational transfer from a photocrosslinkable liquid crystalline polymer (PPLC). Irradiation with linearly polarized light (LPL) 300 nm above the PPLC film followed by an appropriate annealing process led to strong in-plane molecular orientation in the film. The precursor sol solution containing a chromonic forming azo dye and tetraethoxysilane in the presence of an anionic surfactant and 2-(2-aminoethoxy)ethanol was placed onto this aligned film by the static deposition or dipping method. After drying, the chromonic columns hybridized with silica were macroscopically oriented orthogonal to the LPL direction, namely the orientation of the dye molecule being parallel to it. In the dip coating process, a combination of photoalignment and flow induced orientation allowed clear micropatterning of the column orientations, which could be readily discerned when observed with a polarizing film.