Nanoparticle-doped large area PMMA plates with controlled optical diffusion

Abstract

Large-area nanocomposite plates (35 cm × 35 cm × 1 cm) with tuned optical diffusion were successfully prepared. The poly(methyl-methacrylate) matrix is synthesized by bulk polymerization, and “doped” with some ppm of commercial TiO₂ nanoparticles. These are surface modified with 1-octylphosphonic acid in order to stabilize them in the monomer, as shown by repeated Dynamic Light Scattering measurements over long times. TEM images show that the dispersed TiO₂ nanoparticles are aggregated in irregular and porous clusters of about 100 nm in diameter. The size of these aggregates is also confirmed by UV-visible transmission measurements. TEM images of slices prepared from plates confirm that the nanoparticles do not further aggregate during bulk polymerization. Optical diffusion could be characterized in detail, thanks to the large size of the nanocomposites, by using a home-made optical set-up. This allowed the observation of a number of subtle optical effects related to multiple-scattering, and the direct observation of a ‘blue sky effect’ associated with the small size of the nanoparticles involved in diffusion.