Role of Solvent-quality in the Processing of Polymer Nanocomposites on Their Microstructure and Rheological Properties

 The physical properties of polymer nanocomposites (PNCs) generally rely on the microstructures, namely the spatial organization of nanoparticles (NPs) in a polymer matrix. Thus, enormous efforts have been made to control the structure of NPs and thus to obtain desired properties of PNCs. One of the effective methods is to change the initial solvent quality. The initial dispersing solvent is not present in a final state of PNCs but is known to alter their microstructures and mechanical properties, varying polymer chain structures and dynamics, especially at interfaces.

 Here, we propose a simple strategy to control the microstructures of NPs by adding additional solvents with different solvent quality (good/poor) to the initial theta solvent. The microstructure and rheological properties of PNCs were greatly influenced by the additional solvents, as investigated by small-angle X-ray scattering and oscillatory rheometer. When the good solvent is added, the dispersion stability is generally improved. On the contrary, as the addition of poor solvent increases, the dispersion stability of NPs can be decreased yet forming stable clusters or aggregated networks. Thus, we found that the addition of large amounts of poor solvent significantly enhances the mechanical properties of PNCs.