MD Simulation Of Effects Of Chemisorption On The Interfacial Bonding And Characteristics Of Graphene/Polymer Composites

Since the first fabrication of a single graphene sheet using a mechanical cleavage method in 2004, graphene, a two-dimensional sheet of sp2-hybridized carbon system, has been a highlighted material in the past few years due to its exceptional properties. The unique structure, anomalous quantum Hall effect, and the massless Dirac fermion-like charge carriers of graphene make it an ideal material for future electronics such as field-effect transistors and conductive interconnects. Besides, graphene also exhibits great promise for potential applications in many other technological fields such as sensors, composites, membranes for gas separation, and hydrogen storage. After graphene was reported to be the strongest material in the world, and the cost of graphene is much lower, graphene has increasingly attracted attention as a promising candidate to take the position of carbon nanotubes (CNTs) in the reinforcement for polymers mechanical, electrical and thermal properties. Due to the difficulties to devise all kinds of experiments to study the interfacial characteristics of graphene-polymer composites, molecular mechanics (MM) and molecular dynamics (MD) simulations are becoming useful methods to investigate the interfacial reinforcement mechanisms of graphene-polymer composites.The influence of the chemical functionalization of graphene on the interfacial bonding characteristics between the graphene and polymer was investigated using molecular mechanics and molecular dynamics simulations. The simulations show that the bonding energy and shear stress between the graphene and polymer increase with the increase of the concentration of functionalized groups. Besides, our simulations indicated that some specific chemical modifications of graphenes play an important role in determining the strength of interfacial bonding characteristics between the graphene and polymer. Therefore, the attachment of some suitable chemical groups with reasonable concentration to the graphene surface may be an effective way to significantly improve the load transfer between the graphene and polymer when the graphene are used to produce nanocomposites.Furthermore, a crucial issue to design nanocomposites with tailored structure and desired properties is to understand the effects of incorporated inorganic particles in polymers at molecular level. In this study, a"cooling process", performed by molecular dynamics (MD) simulation, was used to predict the glass transition temperature (Tg) of graphene-polymer composites. It was found that additions of functionalized graphenes to a polymer matrix can greatly increase Tg of the composites. The calculation results of the mean square displacement (MSD) of the polymer chains and Tg of the composites showed that the graphenes with functionalizations can intensify the arrest of the chains mobility. Meanwhile, it was found that the thermal expansion of the composites exhibited a relation with the phonon mode vibrations and Brownian motions of the graphene in the polymers. The computational findings of Tg were in good agreement with the experimental results indicating that this computational method can be used to predict effectively the Tg of graphene-polymer composites.Our simulation results, which could reduce the research period and the cost, would be of great importance in the fabrication of graphenes reinforced polymer composites. The results also are critical for many applications of composites materials in the future, such as painting, coating, continuous spinning, weaving, and extrusion of the materials for fabrication purposes.