Molecular dynamics simulation of nanocomposite materials

Mixed-matrix materials are a class of nanocomposites that contain a rigid, inorganic chemical species within a polymer matrix. The addition of the inorganic species necessarily affects the structures and thermal properties of the original polymeric material. In this thesis, mixed-matrix materials containing polymer and polyhedral oligomeric silsesquioxanes (POSS) are studied with molecular dynamics simulation to provide molecular insight about the property enhancements observed experimentally for this class of material.;Three different polymer matrices are considered: glassy polymer (polyimide, PI), flexible polymer (polydimethylsiloxane, PDMS), and a copolymer composed of the glassy and flexible segments. Two different POSS, octahydrido silsesquioxane (OHS) and octaaminophenyl silsesquioxane (OAPS) are studied to observe the effect of different functionalization of POSS in the nanocomposite material. The glass transition temperature of the PI/OAPS, PDMS/OAPS, and PI-PDMS/OAPS blends increases with the incorporation of OAPS. A decrease in the glass transition temperature is shown for the model of PI/OHS blends.;Although the results from the atomistic simulations provide molecular insight about thermal property enhancements afforded by POSS-based additives, there is a limitation of the system size and the time scale being used for such macromolecular system in the atomistic simulation. To overcome this, a coarse-grained (CG) model has been shown to have the capability of eliminating the unimportant degrees of freedom in the atomistic simulation. CG model treats a collection of atoms as a coarse-grained site, and therefore larger system can then be studied at longer time scales. In this work, the CG model for OHS molecule is obtained by using a force-matching method. The CG model is validated by comparing the OHS structural properties obtained from the CG-MD simulation to the one obtained from the atomistic MD simulation.