Simulational studies of formation of polymer layered silicate nanocomposites

Molecular dynamics simulations are performed to investigate the formation mechanisms of polymer-layered silicate nanocomposites. The simulation data are fit to a diffusion model, in which polymer molecules flow into a void space of a fixed volume, to extract an effective diffusion coefficient that characterizes the flow. In qualitative agreement with experiments, the effective diffusion coefficient is shown to decrease with increasing polymer-surface affinity. While increasing polymer-surface affinity has an effect of slowing down the intercalation process, a sufficiently strong polymer-surface affinity is required to drive the polymers into the gap between the silicate sheets. The intercalation kinetics is determined by a balance of the competing factors of friction and driving force. Amphiphilic intercalants such as block copolymers composed of incompatible blocks can be used as a means to enhance the kinetics by effectively increasing the driving force for intercalation. The rather anomalous Rouse-like molecular weight dependence of intercalation kinetics observed in experiments is investigated, and is also attributed to the coupled relation between friction and driving force.