Atomistic modeling and simulation of the mechanical properties of sPMMA - graphene nanocomposites

• Κύριος συγγραφέας: Σκούντζος, Εμμανουήλ - Θεόδωρος
• Άλλοι συγγραφείς: Μαυραντζάς, Βλάσης
• Μορφή: Thesis
• Γλώσσα: English
• Έκδοση: 2014
• Θέματα: Simulation; Molecular dynamics; Graphene; Polymer nanocomposites; Mechanical properties; PMMA; Προσομοίωση; Μοριακή δυναμική; Γραφένιο; Νανοσύνθετα πολυμερικά υλικά; Μηχανικές ιδιότητες; Πολυ (μεθακρυλικός μεθυλεστέρας); 620.192 042 92

Small concentrations of graphene can significantly alter the phase behavior and the mechanical and electrical characteristics of polymeric materials. In this Masters thesis, we present results from a hierarchical simulation methodology that leads to the prediction of the thermodynamic, conformational, structural, dynamic and mechanical properties of polymer nanocomposites. As a model system, we have chosen syndiotactic poly(methyl methacrylate) or sPMMA reinforced with uniformly dispersed graphene sheets. How graphene functionalization affects the elastic constants of the resulting nanocomposite is also examined. The simulation strategy entails three steps: 1) Generation of an initial structure which is subjected to potential energy minimization and detailed molecular dynamics (MD) simulations at T=500K and P=1atm, to obtain well relaxed melt configurations of the nanocomposite and to extract any interested properties. Furthermore, for the sPMMA/graphene nanocomposite: 2) Gradual cooling of selected configurations down to room temperature to obtain a good number of structures representative of its glassy phase, and 3) Molecular mechanics (MM) calculations of its mechanical properties following the method originally proposed by Theodorou and Suter. The MD simulations have been executed with the LAMMPS code using the all-atom DREIDING force-field. By analyzing MD trajectories under constant temperature and pressure, all nanocomposite systems were found to exhibit slower terminal and segmental dynamics than the unfilled ones. The addition of a small fraction of graphene sheets in the polymer matrix led to the enhancement of its elastic constants especially when functionalized graphene sheets were used.