Gradual Solvent Quality Changes Induce Abrupt Changes in Interfacial Layer, Dispersion Structure, and Physical Properties of Polymer Nanocomposites

The polymer interfacial layer, formed by the polymer adsorption onto the surface of nanoparticles (NPs) due to polymer-NP interactions, is well-known to determine the particle dispersion and resulting physical properties of polymer nanocomposites (PNCs). Given that PNC processing generally occurs in the presence of solvents, understanding the influence of solvent quality on the effective polymer-NP interaction is crucial for controlling the microstructure and properties of PNCs. However, the inherent solubility parameter of solvents imposes limitations on systematic analyses based on gradual solvent quality changes. Here, we systematically investigate the role of solvent quality on PNC by using solvent mixtures. We found that the microstructure and physical properties of PNCs varied with the solubility parameter difference between polymer and solvent mixture, suggesting a critical difference of 5 MPa1/2. These changes are attributed to the structure, rather than the dynamics, of the interfacial layer, which originates from the polymer–particle effective interaction. This study emphasizes the critical role of solvent quality in achieving desired PNC properties and offers insights for optimizing process solvents in various applications of polymer-NP suspensions.