Diffraction of Visible Light by Ordered Monodisperse Silica−Poly(methyl acrylate) Composite Films

Abstract

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