Supercritical carbon dioxide assisted dispersion and distribution of silica nanoparticles in polymers

Creating well-dispersed polymer nanocomposites is an important part of controlling composite properties. Nanoparticles have been shown to improve among others electrical, thermal, mechanical, and barrier properties of polymers if they can be dispersed and distributed within the polymer matrix effectively. In the current study, supercritical carbon dioxide is used to disperse and distribute silica nanoparticles in poly(methyl methacrylate), PMMA. It was found that processing silica/PMMA nanocomposite system with supercritical carbon dioxide led to drastic improvement of the dispersion and distribution of silica nanoparticles in PMMA. The state of dispersion and distribution was found to strongly depend on the carbon dioxide saturation pressure – the greater the saturation pressure was, the better the dispersion and distribution became. The dispersion and distribution of silica nanoparticles were quantified via radial distribution function (RDF), which was constructed from transmission electron micrographs. In addition, the non-bonded attraction and cohesive energy between almost-touching nanoparticles were calculated using the Hamaker theory and results were compared with the internal pressure of expanding pores.