Optical Diffraction from Silica−Poly(methyl methacrylate) Composite Films

Abstract

Monodisperse, 152 nm diameter, amorphous, colloidal silica particles in methyl methacrylate (MMA) dispersions form crystal lattices and Bragg diffract visible light. Nucleation, growth, and crystallite morphology are observed by polarizing microscopy. Polymerization of 264 μm thick films of the MMA dispersion traps the crystal order in robust silica−poly(methyl methacrylate) (PMMA) composites. UV−vis spectra of 35−45 wt % of silica coated with 3-(trimethoxysilyl)propyl methacrylate (TPM−silica) in MMA dispersions have low percent transmittance (%T) peaks of 4 nm bandwidth at wavelengths between 550 and 508 nm. The silica−PMMA composite films containing 35−37.5 wt % TPM−silica have low %T peaks at 486−490 nm with 12−19 nm bandwidths. Using a 442 nm helium cadmium laser, the Bragg diffraction of a MMA dispersion and a PMMA composite is observed in the reflective mode.