Abstract
A molecular rheological model for amorphous homopolymers filled with nanoparticles is presented. The fillers are non-agglomerated and interact energetically with the polymers. The model applies to situations in which the polymer-filler affinity is relatively weak. The essential physics represented in the model includes chain reptation, the slowing down of diffusion due to energetic interactions of polymers and fillers, chain stretch, and contour length fluctuations. The model is based on insight obtained from extensive simulations of the structure and dynamics of these systems. The chain population is composed of free, dangling and bridging chains, i.e. those that at given time do not contact fillers, contact one filler or multiple fillers, respectively. As the system evolves, a representative chain switches randomly between these categories. The representative chain reptates only when free, while contour length fluctuations are performed at all times. Relaxation is controlled by both tube renewal and the process of chain attachment/detachment to/from the filler surface. The second process modulates the first, leading to a relaxation with two characteristic times, in agreement with experimental observations. The parameters entering the model can be calibrated based on the rheology of the neat polymer and based on results from simulations of the respective filled system. Keywords: rheology of polymer nano-composites; reptation; contour length fluctuation; tube renewal