Effect of Solvent, Hydrogen Bonding, and thickness of Azopolymer Films on Surface Relief Grating
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Effect of Solvent, Hydrogen Bonding, and thickness of Azopolymer Films on Surface Relief Grating Woo-Hyuk Jung1, Dong-Yu Kim2, Jayant Kumar3, and Stephen P. McCarthy1 1 Department of Plastics Engineering, 3Center for Advanced Materials University of Massachusetts Lowell One University Ave Lowell, MA 01854 2 Department of Materials Science and Engineering Kwangju Institute of Science and Technology One Oryong-dong, Buk-gu, Kwangju 500-712 Korea ABSTRACT Epoxy-based copolymers were synthesized with N,N-diglycidyl aniline (DGA) and aniline (An), called poly(DGA-co-An), where azo coupling reactions were performed using amino benzonitrile (ABN) and nitro aniline (NA). Two azopolymers were dissolved with both tetrahydrofuran (THF)/dioxane complex solvent and THF to compare the diffraction efficiencies according to solvent. The thin films spin-cast with THF/dioxane showed the better diffractive efficiency than with THF due to the high boil point of the residual dioxane. The azopolymers of two azo bonds were spin-coated at 800 and 1300 rpm where the thicker film showed the better diffractive efficiency. The epoxy-based copolymers synthesized with diglycidyl ether of bisphenol A (DGEBA) and aniline (An) or 3-hydroxyl aniline (HAn) were coupled with hydroxyl nitro amino benzene (HNAB). Hydroxyl groups in chromophores helped to form hydrogen bonding with the nitrogen atoms in the azo bonds and prevented photoisomerization, showing no surface relief gratings under a normal laser intensity of 100 mW/cm2. Polyurethanebased azopolymers were synthesized with disperse orange 17 (DO17) and toluene-2,4diisocyanate (TDI), which were no hydroxide groups in the main chains, and showed the better diffractive efficiency than the epoxy-based azopolymers with nitro substituents. INTRODUCTION Surface relief grating is a surface roughness created by the interference patterns of a polarized and cohesive laser beam, showing holographic light birefringence. The prominence and depression are inscribed by the reinforced and destructive waves of laser beams, while round groove patterns are created by a single polarized laser beam. The first study on the surface relief grating was started with epoxy-based azopolymers by D. Y. Kim et al. [1] and another independent study was carried out with polyarylate-based azopolymers by P. Rochon et al. [2]. Azopolymers were photo-induced to transform from trans into cis isomers that caused unevenness on the thin film surfaces, which were responsible for light scattering to show holographs. Surface relief gratings were derived from the studies on non linear optic polymeric materials based on azobenzene chromophores. The other applications on azobenzene chromophores are photorefractivities [3], all-optical polings, photo-assisted polings, optical data storages based on photochromism [3-5], liquid crystals with azobenzenes, and reversible optical waveguides [2-3]. The thin layers of azopolymers forming reflective layers for optical data storages need to show fast initial responses on a laser beam, sig
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