Investigation into the Atomistic Scale Mechanisms Responsible for the Enhanced Dielectric Response in the Interfacial Region of Polymer Nanocomposites

In this contribution, we report on the nanoscale mechanisms responsible for enhancing the dielectric constant in the interfacial region of polymer-based nanocomposites. Recent experiments indicate that the dielectric constant of a polymer matrix can be significantly increased by adding minute concentrations of inorganic nanofillers; this behavior is not described by available analytical models, as the low concentration of fillers is a negligible factor in volume-averaged models and most likely the enhancement is due to interfacial effects. To understand the origins of the augmented dielectric response in these nanocomposites, a theoretical model was developed, which permitted us to find a direct correlation between the dielectric properties and the mobility of the polymer chains. In addition to the theoretical framework, molecular dynamics simulations were implemented to verify the relationship between the dielectric constant and the mobility of the polymer. Further atomistic simulations were performed for the interface between the polymer and the inorganic nanofillers to assess the interfacial effects on the dielectric properties. High and low polymer mobility regions were identified in the interfacial region. The high mobility region showed a vibrational behavior similar to a fluid, while the vibrational characteristics of the low mobility region resembled a solid. The nanofiller induced free volume and shorter polymer chains, which led to an increase in the dielectric constant. It is thus predicted that nanofiller-induced modifications leading to increased interfacial polymer mobility and short intermingled chains will enhance the dielectric constant, making polymer-based nanocomposites suitable for the next generation of capacitors.