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Materials 2016, 9(3), 188; doi:10.3390/ma9030188

Spatial Frequency Responses of Anisotropic Refractive Index Gratings Formed in Holographic Polymer Dispersed Liquid Crystals

Department of Engineering Science, University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan
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Academic Editor: Manuel Francisco Ortuño Sánchez
Received: 31 January 2016 / Revised: 24 February 2016 / Accepted: 29 February 2016 / Published: 10 March 2016
(This article belongs to the Special Issue Photopolymers for Holographic Applications)
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Abstract

We report on an experimental investigation of spatial frequency responses of anisotropic transmission refractive index gratings formed in holographic polymer dispersed liquid crystals (HPDLCs). We studied two different types of HPDLC materials employing two different monomer systems: one with acrylate monomer capable of radical mediated chain-growth polymerizations and the other with thiol-ene monomer capable of step-growth polymerizations. It was found that the photopolymerization kinetics of the two HPDLC materials could be well explained by the autocatalytic model. We also measured grating-spacing dependences of anisotropic refractive index gratings at a recording wavelength of 532 nm. It was found that the HPDLC material with the thiol-ene monomer gave higher spatial frequency responses than that with the acrylate monomer. Statistical thermodynamic simulation suggested that such a spatial frequency dependence was attributed primarily to a difference in the size of formed liquid crystal droplets due to different photopolymerization mechanisms. View Full-Text
Keywords: holographic polymer dispersed liquid crystal; photopolymer; nematic liquid crystal; phase separation; holographic grating formation; Bragg grating holographic polymer dispersed liquid crystal; photopolymer; nematic liquid crystal; phase separation; holographic grating formation; Bragg grating
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Fukuda, Y.; Tomita, Y. Spatial Frequency Responses of Anisotropic Refractive Index Gratings Formed in Holographic Polymer Dispersed Liquid Crystals. Materials 2016, 9, 188.

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