Emulsion Polymerization, Size Determination, and Self-Assembly of Monodispersed Poly(methyl methacrylate) Nanospheres for Photonics

Polymers and nanochemistry are important facets of chemistry. In this experiment, students synthesize monodispersed poly­(methyl methacrylate) nanospheres from the addition or chain polymerization of a rapidly stirred aqueous mini-emulsion of methyl methacrylate. The 2,2′-azobis­(2-methylpropion­amidine) dihydrochloride serves as a heat activated, water-soluble, free radical initiator to polymerize the emulsion droplets starting from their outer edge. The uniform small diameter particles will appear iridescent if they are close-packed and their size is similar to the wavelength of visible light. Students characterize the size of the poly­(methyl methacrylate) spheres by four methods: the settling velocity and Stokes’ law, evaporative self-assembly of a photonic material and visible spectroscopy, direct measurement using scanning electron microscopy (SEM), and SEM measurement of the silica inverse opal. This experiment increases student collaboration and provides the opportunity to work on multiple experiments at once.