Effect of Interfacial Energetics on Dispersion and Glass Transition Temperature in Polymer Nanocomposites

Developing structure–property relationships between the filler/matrix interface chemistry and the dispersion and interface properties of polymer nanocomposites (PNC) is critical to predicting their bulk mechanical, electrical, and optical properties. In this paper we develop quantitative relationships between interfacial surface energy parameters and the dispersion and Tg shifts of PNCs through systematic experiments on an array of hybrid systems spanning a wide range of interfacial interactions. We use four different matrices of surface energies varying from polar to nonpolar (poly(2-vinylpyridine) (P2VP), poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA), and polystyrene (PS)), filled with three monofunctional-silane modifications of colloidal silica nanospheres (octyldimethylmethoxysilane, chloropropyldimethylethoxysilane, and aminopropyldimethylethoxysilane). We hypothesize the ratio of the work of adhesion between filler and polymer to the work of adhesion of filler to filler (WPF/WFF), in conjunction with the relative work of adhesion (ΔWa), can be used to predict the final state of particle dispersion. Additionally, the direction and magnitude of Tg deviation from the neat polymer are hypothesized to depend on the work of spreading (Ws) and the dispersion state. Our results suggest a strong and moderate dependence of dispersion on WPF/WFF and ΔWa, respectively. Ws in conjunction with the dispersion parameters is shown to dictate the change in Tg. Our model represents a significant step toward realizing a priori nanocomposite property prediction.