Thermodynamics of Binary and Ternary Polymer Blend Nanocomposites

Polymer nanocomposites (PNC), which are a combination of organic and inorganic fillers and a polymer matrix, have found great scientific interest due to the fact that the material properties of the PNC are largely determined by the chemical composition of the polymer as well as the type of fillers. While the fundamental physics governing the phase space of polymer blends is mature, there is a significant lack of understanding of the thermodynamics and kinetics that govern PNCs. In this work, we investigate model binary and ternary nanocomposites of poly(methyl methacrylate) grafted silica nanoparticles (PMMA NP), poly(styrene-ran-acrylonitrile) (SAN), and poly(methyl methacrylate) as a platform to elucidate the governing thermodynamic contributions. The thermally annealed films were characterized using electron microscopy and x-ray scattering, revealing lower critical solution temperature (LCST) behavior in the binary composite and an increased miscibility window in off-critical compositions for the ternary. These results extend the current understanding of PNC phase behavior and allow for greater control over NP dispersions.