Molecular Dynamics Simulation Investigation Of Intermolecular Interactions For Functionalized Graphene Sheets/Polymers Systems

Graphene sheets—one atom-thick two-dimensional layers of sp2-bonded carbon have a range of unusual mechanical, thermal and electronic properties. The unique mechanical property of graphene sheet has attracted a number of international research institutes to perform their investigations in the area of reinforcement materials. In this thesis, molecular dynamics simulations based the COMPASS force field are applied to investigate the intermolecular interactions between graphene sheets and different polymer molecules. The influence of structure and conformation of the polymer and graphene width on polymer adhesion is investigated. Furthermore, the cross couplings between functionalized graphene sheets and polymer chains are examined.The results of simulations show that the interaction between the graphene sheet and the simulated polymer is significantly influenced by the specific monomer structure and conformation of the polymer. The polypyrrole (PPy) and polyimide (PI) having aromatic rings strongly interact with graphene sheets. Theπ–πinteraction is the key for the strong interfacial adhesion between sheets and polymer molecules. To maintain the original helical conformation, the equilibrium adsorbed conformations of the polyphenylacetylene (PPA) have optimal helical conformations and form random wrapping conformations when it interacts with the graphene and single-walled nanotube (SWNT). In addition, the results of simulations indicate that the interaction energy (IE) between the graphene sheet and the polymer molecule is obviously influenced by the width of the graphene. For the PPy and PI molecules, when the graphene width is less than 2 nm, the IE increases with increasing width and has the maximum at 2 nm. After that, the IE decreases with increasing width if the graphene width is greater than 2 nm. For the Polymethylmethacrylate (PMMA) molecule, when the graphene width is less than 3 nm, the IE increases with increasing width and reaches the maximum at 3 nm. From this point onward, the IE decreases with increasing width. However, the effect of the graphehe width on the IE for the polyethylene/graphene system is very weak. It is concluded that when polymers with the different atom numbers and/or different molecular structures interact with graphene sheets, there will be an optimal graphene width for such system.In this dissertation, the simulations also indicate that uneven functional planes of functionalized graphene sheets may form the cross coupling interaction with polymers. In that case, when the outside force exerts on the simulated system, the uneven functional plane of functionalized graphene sheet will generate the force on the polymer. Such force will hinder the interaction substances of the simulated system apart from each other. Therefore, it has some reasons to believe that the nanocomposites should have high mechanical properties if the functionalized graphene sheet with an appropriate functional group is used to form the strong interfacial adhesion with the polymer.