Interfacial dynamics of polymer nanocomposites: the roles of chemical heterogeneity

Polymer at the interface is the key to the mechanical and viscoelastic properties of polymer nanocomposites. Significant efforts have been performed in the past on polymer dynamics near inorganic solid interfaces. In contrast, polymer dynamics at the soft interface have received much less attention. In this contribution, we synthesize and prepare poly(methyl methacrylate) (PMMA) grafted Fe₃O₄ nanoparticles and disperse them in a poly(methacrylate) (PMA) matrix with different polymer molecular weights. Broadband dielectric spectroscopy has been employed to quantify the interfacial dynamics over a wide range of temperatures. Significant broadening of dielectric dispersion of the segmental relaxation of the PMA is observed which can be attributed to the interface slowing down in contact with glassy PMMA, which also exhibits a strong dependence on the molecular weight of the PMA matrix. Interestingly, only a mild slowing down in structural relaxation of PMA is observed over the temperature range of our measurements. On the other hand, significant acceleration has been observed in both the secondary relaxation and the glassy dynamics of grafted PMMA. These observations highlight an interesting interplay between the dynamics of grafted PMMA and that of PMA that is not anticipated in polymer/solid interface.