Synthesis and Fabrication of Multifunctional Nanocomposites: Stable Dispersions of Nanoparticles Tethered with Short, Dense and Polydisperse Polymer Brushes in Poly(methyl methacrylate)

iron oxide, [ 10 ] zinc oxide, [ 11 ] cadmium selenide, [ 12 ] gold [ 13 ] and others in nanocomposites is a promising approach to introduce new functionalities to a polymer such as tunable refractive index, magnetism, surface hardness, UV absorption, etc. However, aggregation of nanoparticles is commonly encountered, leading to unsatisfactory performance of nanocomposites and frustrating efforts to utilize functional nanoparticles in applications. Many approaches exist to alleviate the aggregation problem. Amongst them, the polymer brush/nanoparticle system remains the most promising. This is due to the fact that numerous examples of stable and highly dispersed nanoparticles in nanocomposites already exist. Such stable dispersions work through the “wetting-dewetting” phenomenon of polymer brushes. Wetting of the brush by free polymer chains ensures a good dispersion while dewetting of the brush, forming the so-called “dry brush”, encourages aggregation of the nanoparticles. Wetting occurs when free polymers mix freely with the grafted polymer brush; conversely, dewetting occurs when free polymers do not penetrate into the brush and as a consequence, no mixing happens. In the absence of enthalpic effects, i.e. interactions due to different brush-matrix chemical structures, and other effects such as magnetic or electrostatic attractions, the dispersion of polymer-grafted nanoparticles in a chemically identical matrix is determined by entropic factors. Existing studies done on polymer brushes on fl at [ 14 ] Synthesis and Fabrication of Multifunctional Nanocomposites: Stable Dispersions of Nanoparticles Tethered with Short, Dense and Polydisperse Polymer Brushes in Poly(methyl methacrylate)