Photoinduced Opposite Diffusion of Nematic and Isotropic Monomers during Patterned Photopolymerization

Films containing a photoreactive mixture of a liquid-crystalline diacrylate and an isotropic monoacrylate were UV exposed by means of lithographic and holographic techniques, resulting in a spatial intensity distribution in the films. The favored depletion of the more reactive diacrylate at sites with maximum UV intensity results in preferred diffusion of this monomer to these areas. The monoacrylate oppositely diffuses to the sites with minimum intensity which, depending on polymer ratios and liquid-crystalline transition temperatures, eventually leads to a phase transition from the nematic to the isotropic phase. In this way holographic gratings were prepared exhibiting high diffraction efficiencies due to the alternation of lines of optically oriented and of isotropic materials. The diffusion process was successfully simulated by a simple polymerization and diffusion model and was verified by fluorescent labeling experiments in combination with fluorescence microscopy.