Influence of the molecular level structure of polyethylene and polytetrafluoroethylene on their tribological response

Crosslinks occur in polymers following irradiation and are used in computational simulations to mimic the effects of chain tangling. Here, the effect of crosslink density on the tribological behavior of atomic-scale models of polyethylene and polytetrafluoroethylene is determined using classical molecular dynamics simulations. In the simulations, oriented crosslinked surfaces are slid in different directions over a range of applied normal loads. The results indicate that, at the same normal load, the friction force increases with increased crosslink density. In addition, the influence of randomized versus ordered crosslinking on the simulated tribological behavior is investigated. Finally, the influence of crosslink density on the simulated wear mechanisms of polyethylene and polytetrafluoroethylene is elucidated. The results have important implications for the atomic-scale modeling of friction at the interfaces of polymers that have been irradiated or contain entangled chains.