Phase behavior of polymer-grafted nanoparticle blend films via thermal and solvent vapor annealing

While chemically similar polymer-grafted nanoparticle (PGNPs) blends can offer enhanced material properties compared to their homopolymer analogs, such as in preventing film crack propagation, the phase behavior and mechanical behavior of chemically dissimilar PGNPs have not been explored. Generally, we expect this to depend on nanoparticle size(ro), polymer grafting density, brush segmental interactions, and polymer inorganic core interaction parameters. Both enthalpic and entropic (conformational and mixing) interactions between the polymer chains can play an essential role in the phase behavior of the PGNP blend system, while kinetics will determine their final domain or mixed state structure. As thermal annealing (TA) may be challenging to enable high mobility in large PGNP systems, we utilize alternate methods, such as solvent vapor annealing (SVA) and Direct immersion annealing (DIA), to process dissimilar binary PGNP systems of polymethyl methacrylate silica (PMMA-SiO2) and polystyrene acrylonitrile blend silica (PSAN-SiO2) (acrylonitrile content = 13%). Atomic force microscopy is used to characterize the surface topography and mechanical contrast of the thin films to identify phase behavior for different processing temperatures, film thickness, and annealing time. Results on kinetics and phase behavior of PGNP blends and their mechanical modulus by the SIEBIMM method will be discussed.