Thermal conductivity via atomistic modeling for epoxy-SWNT composites

Abstract

The Green-Kubo method was used to investigate the thermal conductivity as a function of temperature for epoxy/single wall carbon nanotube (SWNT) nanocomposites. An epoxy network of DGEBA-DDS was built using the ’dendrimer’ growth approach, and conductivity was computed by taking into account long-range Coulombic forces via a kspace approach. Thermal conductivity was calculated in the direction perpendicular to, and along the SWNT axis for functionalized and pristine SWNT/epoxy nanocomposites. Inefficient phonon transport at the ends of nanotubes is an important factor in the thermal conductivity of the nanocomposites, and for this reason short, discontinuous nanotubes were modeled in addition to long nanotubes. The thermal conductivity of the long, pristine SWNT/epoxy system is equivalent to that of a SWNT along its axis, but there was a 27% reduction perpendicular to the nanotube axis. The functionalized, long SWNT/epoxy system had a very large increase in thermal conductivity along the nanotube axis (∼700%), as well as the directions perpendicular to the nanotube (64%). The discontinuous nanotubes displayed an increased thermal conductivity along the SWNT axis compared to neat epoxy (103% for the pristine SWNT/epoxy, and 91% for functionalized SWNT/epoxy system). The functionalized, discontinuous system also showed a 42% improvement perpendicular to the nanotube, while the pristine, discontinuous SWNT/epoxy system had no improvement over epoxy. These simulations demonstrate there exists a threshold of the SWNT length where the best improvement for a composite system would transition from pristine SWNTs to functionalized SWNTs.