(726d) Comparison of Coarse-Grained Approaches in Predicting Polymer Nanocomposite Phase Behavior

Authors: 
Koski, J. P., Sandia National Laboratories
Ferrier, R. C. Jr., University of Texas at Austin
Krook, N. M., University of Pennsylvania
Chao, H., University of Pennsylvania
Composto, R. J., University of Pennsylvania
Frischknecht, A. L., Sandia National Laboratories
Riggleman, R. A., University of Pennsylvania
Polymer nanocomposites (PNCs) show promise in the development of complex materials with advanced properties that range from tough lightweight materials, drug delivery vesicles, photovoltaic devices, and transparency or stealth applications. The functionality and properties of PNCs are dependent on the arrangement and assembly of nanoparticles within the matrix polymer. However, the considerable parameter space associated with PNCs requires efficient theoretical and simulation methods to understand their assembly and guide experiments. Unfortunately, theoretical and simulation methods are restricted in their ability to accurately map to experiments due to approximations and numerical limitations. In this study, we provide direct comparisons of three coarse-grained approaches for modeling PNCs, two equilibrium methods and one non-equilibrium method.

In conducting the direct comparison, we are able to systematically study the impact of many-body effects, random versus uniform grafting of polymers on the nanoparticles, and thermal fluctuations on the large-scale phase behavior of grafted nanoparticles in a polymer matrix. Additionally, we provide a qualitative comparison of the three methods to experiments consisting of polystyrene grafted gold nanorods in a polymethyl methacrylate matrix. For large matrix molecular weights, when the nanoparticles are randomly initialized in the non-equilibrium method, the nanoparticles coarsen into larger clusters, similar to the experiments. However, when the non-equilibrium simulations are initially biased as a single aggregate, the particles remain macrophase separated from the matrix over the course of the simulation. This indicates the experiments are in a non-equilibrium state. In using these coarse-grained approaches, we are able to describe and discern the thermodynamic versus non-equilibrium nature of PNCs.