Structure and dynamics of blends of polyhedral oligomeric silsesquioxanes and polyethylene by atomistic simulation

The influence of blending polyhedral oligomeric silsesquioxane substituted with cyclopentyl rings (CpPOSS) into a polyethylene (PE) matrix was probed using atomistic simulations. Composites of 5, 15, and 25 wt % CpPOSS were simulated. Interactions between POSS particles were found to promote organization of POSS within the polymer, where clear signs of aggregation were observed. Both particle and polymer dynamics were monitored. Particular attention was given to the structure and dynamics of the interface between particle and polymer. The interface was found to consist of a 3-5 angstrom thick shell in which the structure of the matrix was altered from that of the bulk. In this region, the local polymer backbone orientation is biased toward a configuration parallel to the particle surface. Dynamically, the interface consists of a thick shell about 11 angstrom thick in which polymer mobility is damped in the direction normal to and enhanced circumferentially to the surface of the CpPOSS particle. These results suggest that the CpPOSS particles exert an influence on the matrix material which mimics the effects of a rigid surface. A potential of mean force between CpPOSS particles in a polyethylene matrix at 500 K is derived from these atomistic simulation results.