Interaction energy and polymer density profile in nanocomposites: a coarse grain simulation based on interaction stress

Abstract

A coarse grain approach was selected to simulate nanocomposites made of single-walled carbon nanotubes (SWNTs) and poly(methyl methacrylate) (PMMA). Unlike common coarse grain simulations, which employ Lennard-Jones models as the force field between the beads, the current approach used experiment-based data, and hence is considered a semi-empirical approach. Interaction stress data obtained from atomic force microscopy experiments under water were multiplied by ten to represent the interaction stresses in vacuum and then fed into the simulation. A new planar approach was introduced to simplify the three-dimensional unit cell into a two-dimensional plane. Furthermore, preliminary one-dimensional simulations were carried out to acquire a trade-off between simulation time and accuracy of the results. It was shown that the final results were independent of the initial conditions and converging parameters (the parameters that define the convergence rate). Two sets of planar simulations were performed to model pure PMMA systems and PMMA–SWNT nanocomposites. Polymer chain configuration and density profiles for these systems were obtained and compared. The surface effect on the polymer configuration and density profile was captured and demonstrated to be identical for the two systems. The polymer simulations showed a core section with a constant density, where the surface effect from the free surface did not influence the behaviour of the polymer chains. The effect of nanotube on polymer morphology was observed by layered structures of polymer chains around the nanotube, with preferable bands of peaks and valleys in the radial density profile. Finally, a new method was presented to calculate the interfacial binding energy for nanocomposites. The value of 0.44 kcal mol⁻¹ Å⁻² obtained for the PMMA–SWNT nanocomposite was shown to be in good agreement with the previously reported results obtained from atomistic simulations.