Interfacial thermal transport and structural preferences in carbon nanotube-polyamide-6,6 nanocomposites: how important are chemical functionalization effects?

We employ reverse nonequilibrium molecular dynamics simulations to investigate the interfacial heat transfer in composites formed by an ungrafted or a grafted carbon nanotube which is surrounded by oligomeric polyamide-6,6 chains. The structural properties of the polymer matrix and the grafted chains are also studied. The influence of the grafting density, the length of the grafted chains as well as their chemical composition on the interfacial thermal conductivity (lambda(i)) are in the focus of our computational study. For the considered grafted polyethylene and polyamide chains we do not find a sizeable difference in the observed lambda(i) values. In contrast to this insensitivity, we predict a rather strong influence on lambda(i) by the grafting density and the length of the grafted chains. This dependence is an outcome of modifications in the structural properties of the polymer matrix as well as the grafted chains. Functionalization of the nanotube has a sizeable influence on the interfacial thermal conductivity. Its enhancement is caused by the chemical bonds between the nanotube and grafted chain atoms which reduce the number of Kapitza resistances hindering the heat transfer in polymer samples. The phonon density of states profiles confined to the bonded nanotube and the grafted chain atoms are used to emphasize the phonon support of the thermal conductivity in nanocomposites with grafted tubes. Strategies to tailor nanotube containing composites with higher thermal conductivities than that realized in the bare polymer are shortly touched.