Effect of Chemical Heterogeneity and Architecture of the Interphase on the Rheological Behavior of Polymer Nanocomposites

Polymer surface-modified nanoparticles have been widely used to tune the mechanical properties of polymer matrices not only because of the improved dispersion state but also the abundant dynamic variation of the polymers in the interfacial region. Our group explores the effect of chemical heterogeneities and varying chain architectures around nanoparticles on tuning the dynamics of particles and interfacial polymers, hence the mechanical properties. Iron oxide (Fe₃O₄) nanoparticles adsorbed or grafted with poly(methyl methacrylate) (PMMA) chains dispersed in poly(methyl acrylate) (PMA) matrices are prepared and their rheological behavior is characterized. It shows that short adsorbed chains lead to thermal-stiffening, whereas long adsorbed chains yield softening with increasing temperature. A similar trend is found in the systems with larger particle size but with less confined particle diffusion. Conformations and dynamics of adsorbed and grafted chains are discussed to reveal this unusual behavior that relies on interfacial heterogeneities. In addition, other types of adsorbed chains of PA and P2VP, with decreasing rigidity, are compared to understand the role of rigid chains on interfacial dynamics and relaxations.