Holographic Polymer-Dispersed Liquid Crystals and Polymeric Photonic Crystals Formed by Holographic Photolithography

摘要

The present article describes the experimental and theoretical observations on the formation of holographic,polymer-dispersed,liquid crystals and electrically switchable,photonic crystals.A phase diagram of the starting mixture of nematic liquid crystal and photo-reactive triacrylate monomer was established by means of differential scanning calorimetry (DSC)and cloud point measurement.Photolithographic patterns were imprinted on 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 numerical simulation were carried out based on the combination of Flory-Huggins free energy of mixing and Maier-Saupe free energy 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-temporal structure 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 various beam-geometries.Electro-optical performance such as diffraction efficiency was evaluated during the pattern photopolymerization process and also as a function of driving voltage.