Gradual Solvent\nQuality Changes Induce Abrupt Changes\nin Interfacial Layer, Dispersion Structure, and Physical Properties\nof Polymer Nanocomposites

The polymer interfacial layer, formed by the polymer\nadsorption\nonto the surface of nanoparticles (NPs) due to polymer-NP interactions,\nis well-known to determine the particle dispersion and resulting physical\nproperties of polymer nanocomposites (PNCs). Given that PNC processing\ngenerally occurs in the presence of solvents, understanding the influence\nof solvent quality on the effective polymer-NP interaction is crucial\nfor controlling the microstructure and properties of PNCs. However,\nthe inherent solubility parameter of solvents imposes limitations\non systematic analyses based on gradual solvent quality changes. Here,\nwe systematically investigate the role of solvent quality on PNC by\nusing solvent mixtures. We found that the microstructure and physical\nproperties of PNCs varied with the solubility parameter difference\nbetween polymer and solvent mixture, suggesting a critical difference\nof 5 MPa<sup>1/2</sup>. These changes are attributed to the structure,\nrather than the dynamics, of the interfacial layer, which originates\nfrom the polymer–particle effective interaction. This study\nemphasizes the critical role of solvent quality in achieving desired\nPNC properties and offers insights for optimizing process solvents\nin various applications of polymer-NP suspensions.