| Περίληψη: | 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.
|
|---|
