Thermal Conductivity of Polyamide-6,6 in the Vicinity of Charged and Uncharged Graphene Layers: A Molecular Dynamics Analysis

The thermal conductivity (lambda) of nanoconfined polyamide-6,6 (PA) oligomers in polymer-graphene nanocomposites has been investigated by reverse nonequilibrium molecular dynamics (RNEMD) simulations. The preferential alignment of the PA chains parallel to the graphene plane as well as their elongation implies that lambda of the polymer in nanocomposites is larger than that in the neat polymer system. The ordering of the polymer phase is enhanced in an arrangement of charged graphene surfaces made of one layer with a charge deficit and one with a charge excess. The consequence of the enhanced polymer ordering as well as the denser packing is an increase in lambda in the polymer network. Differences in the thermal conductivity for an armchair and zigzag arrangement of the graphene sheets in the direction of the heat transfer are almost negligible. In contrast with this insensitivity, the present RNEMD simulations predict the largest value of lambda for composites with the smallest number of PA chains between adjacent graphene sheets. The modifications in the polymer thermal conductivity are rationalized via several structural parameters such as PA bond orientation relative to the graphene sheets, end-to-end distance of polymer chains, and density profiles.