Role of Chemical Heterogeneity in Bound Layers on the Mechanical Properties of Polymer Nanocomposites

We recently showed that chemical heterogeneity of interfacial layers around particles governs the mechanical properties of polymer nanocomposites. Poly(vinyl acetate) (PVAc) adsorbed silica nanoparticles in two different matrices, poly(ethylene oxide) (PEO) and poly(methyl acrylate) (PMA) matrices are investigated in rheology and small-angle X-ray scattering. Dynamic coupling that is governed by entanglements and interactions between two polymers is enhanced with the short PMA matrix and the long PVAc adsorbed chains on particles. In the PEO system, short adsorbed chains of PVAc reinforced the composite more than the other chain lengths. Our results show that miscibility and attractions between adsorbed and matrix chains in interfacial layers lead to their unusual reinforcement. The results suggest that packing of chains at interface layers may contribute to the reinforcement effect. Composites under large oscillatory deformations are thus examined to reveal the enhancement of mixing, molecular attractions and density of interfaces between adsorbed and matrix chains under shear.