DIFFRACTION OF VISIBLE-LIGHT BY ORDERED MONODISPERSE SILICA-POLY(METHYL ACRYLATE) COMPOSITE FILMS

Composites of ordered colloidal crystals of amorphous monodisperse sil ica particles in amorphous poly(methyl acrylate) (PMA) films selective ly Bragg diffract visible light. The 153 nm diameter colloidal silica particles coated with 3-(trimethoxysilyl)propyl methacrylate form coll oidal crystals in methyl acrylate (MA) monomer, and the crystal order is locked into place by polymerization of the MA. Bragg diffraction fr om the films is detected spectrophotometrically as narrow peaks of low percent transmission of visible light normal to the film plane. The d iffraction wavelength is tuned by varying the d spacing of the crystal lattice and by varying the Bragg angle. Variation in the lattice spac ing is achieved via the particle size or particle concentration, uniax ial stretching of the composite, and swelling the composite with monom ers such as styrene or MA followed by photopolymerization of the imbib ed monomers. Films that diffract from 434 to 632 nm have been prepared .