Chemical Heterogeneities and Architectures of Interfacial Layers in Polymer Nanocomposites*

Polymer coated nanoparticles have been widely used to achieve good dispersion in polymer matrices. Dynamics and glass-transition temperature of bound interfacial layers on nanoparticles of different sizes have been recently investigated to understand the effect of interfacial relaxations as they govern reinforcement in composites. We investigate the effect of chemical heterogeneities and varying chain architectures around nanoparticles on tuning the dynamics of interfacial polymers, hence the mechanical properties such as thermal-stiffening. Fe₃O₄ nanoparticles adsorbed or grafted with PMMA chains and dispersed in PMA matrices are prepared and their rheological behavior is characterized. Our findings show that short adsorbed chains lead to thermal-stiffening, whereas long adsorbed chains yield softening with increasing temperature. Conformations of adsorbed and grafted chains on the same particle sizes will be discussed together to reveal this unusual behavior which relies on the interfacial chemical heterogeneities in polymer nanocomposites. Further, other types of adsorbed chains of PA, P2VP, PMMA, with decreasing rigidity, are compared to understand the role of rigid chains on interfacial dynamics and relaxations.