Effect of Interfacial Regions and Surface Functional Groups on Chemical Transport in Polymer–Particle Composites

Abstract

Improved chemical resistance of polymer-based composites such as coatings remains a significant challenge for many defense applications and technologies. In particular, composites with high concentrations of large, micrometer-size particles present a complex microstructural landscape of competing processes that influence the transport of penetrant molecules. We present results of molecular dynamics calculations designed to model micrometer-size particle surfaces that have been modified by the addition of functional groups. The effect of the functionalized surfaces on the surrounding polymer binder and the diffusive transport of penetrant molecules is examined for different chemistries through a polymer–particle composite system designed to represent an interfacial region. We directly calculate penetrant diffusion coefficients and polymer–penetrant properties within the composite interface and compare with simulations of the same polymer in bulk systems. In the simulations of the composite interface, the equilibrated polymer density is 10–15% less than in the corresponding bulk system, and at room temperature the penetrant diffusivity is found to be more than an order of magnitude greater in the composite interface. In the systems studied here, amine functional groups are seen to have only a secondary effect on transport while no change is observed by the presence of carboxyl groups.