Molecular dynamics simulations of the effect of the volume fraction on unidirectional polyimide-carbon nanotube nanocomposites

Molecular dynamics (MD) simulations were used to predict the effect of the reinforcement volume fraction on a unidirectional nanocomposite comprised of a polyimide and multi-walled carbon nanotubes (MWCNTs). We derived a modified volume fraction equation that takes the interface into account, and thus can precisely calculate the volume fraction of the reinforcement. From the MD simulations, both the stress and the modulus are predicted to increase with increasing number of MWCNTs as a function of a constantly applied strain, although some interesting observations were made in comparison to a pure polyimide system that is ordered, akin to the pre-nucleated crystalline system. In addition, we developed an approach to indirectly predict the change in the degree of order in the matrix with the addition of the CNT reinforcements. The results suggest that the degree of ordering increases with an increase in the volume fraction of MWCNTs, especially at the polymer-CNT interface according to number density plots of the polymer, which is consistent with the hypothesis that CNTs can act as nucleation sites for the crystallization of the polymer matrix.