화학공학소재연구정보센터
Macromolecular Research, Vol.14, No.2, 155-165, April, 2006
Holographic Polymer-Dispersed Liquid Crystals and Polymeric Photonic Crystals Formed by Holographic Photolithography
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The present article describes the experimental and theoretical observations on the formation of holo-graphic, polymer-dispersed, liquid crystals and electrically switchable, photonic crystals. A phase diagram of thestarting mixture of nematic liquid crystal and photo-reactive triacrylate monomer was established by means ofdifferential scanning calorimetry (DSC) and cloud point measurement. Photolithographic patterns were imprintedon the starting mixture of LC/triacrylate via multi-beam interference. A similar study was extended to a dendrimer/photocurative mixture as well as to a single component system (tetra-acrylate). Theoretical modeling and numericalsimulation were carried out based on the combination of Flory-Huggins free energy of mixing and Maier-Saupe freeenergy of nematic ordering. The combined free energy densities were incorporated into the time-dependent Ginzburg-Landau (Model C) equations coupled with the photopolymerization rate equation to elucidate the spatio-temporalstructure growth. The 2-D photonic structures thus simulated were consistent with the experimental observations.Furthermore, 3-D simulation was performed to guide the fabrication of assorted photonic crystals under variousbeam-geometries. Electro-optical performance such as diffraction efficiency was evaluated during the patternphotopolymerization process and also as a function of driving voltage.
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