The Interfacial Zone Around Nanoparticles in Polymer Nanocomposites and Its Relation to the Average Scale of Collective Motion within the Polymer Matrix

There has been much interest in quantifying the spatial scale over which the interfacial dynamics of glassy materials is perturbed by the presence of solid substrates and nanoparticles and in factors that influence the dynamics within this “interfacial zone”. In general, there are many interfacial zones to consider in thin polymer films and nanocomposites, but we focus on the interfacial zone about nanoparticles (NPs) in a polymer matrix, a topic of intense recent experimental investigation because of the relevance of such layers for achieving significant property changes in polymer materials. We model our nanocomposites using a coarse-grained model of both the NPs and the polymer matrix that we have studied extensively in the past. We find that the width ξ of the interfacial zone about the NPs is typically on the order of a few nm and that this scale grows progressively upon cooling where the temperature dependence and order of magnitude of the interfacial zone are in qualitative accord with estimates by Sokolov and coworkers, and others. We also find that the NP interfacial zone scale ξ grows nearly linearly with the extent of string-like collective motion within the film, as found before for the interfacial zone near the polymer-air interface of thin supported polymer films.