PHOTOINDUCED OPPOSITE DIFFUSION OF NEMATIC AND ISOTROPIC MONOMERS DURING PATTERNED PHOTOPOLYMERIZATION

Films containing a photoreactive mixture of a liquid-crystalline diacr ylate and an isotropic monoacrylate were UV exposed by means of lithog raphic and holographic techniques, resulting in a spatial intensity di stribution in the films. The favored depletion of the more reactive di acrylate at sites with maximum UV intensity results in preferred diffu sion of this monomer to these areas. The monoacrylate oppositely diffu ses to the sites with minimum intensity which, depending on polymer ra tios 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 ef ficiencies due to the alternation of lines of optically oriented and o f isotropic materials. The diffusion process was successfully simulate d by a simple polymerization and diffusion model and was verified by f luorescent labeling experiments in combination with fluorescence micro scopy.