Viscoelastic Response of Branched Polyethylene Combs: A Molecular Dynamics (MD) Simulation Study

Polymers exhibit distinctive rheological behavior depending on their architecture. Addition of small number of branches is sufficient to affect the rheology of polymers compared to their linear counterpart with the same molecular weight. Here, using coarse grained molecular dynamics simulations we resolve the effects of the branch length and branch density on the viscoelastic response of entangled polyethylene (PE) melts with branch lengths above and below the entanglement length. The stress relaxation behavior is measured following a small perturbation and from the stress autocorrelation function using the Green-Kubo relation. We find that the plateau modulus is sensitive to both branch length and branch density and decreases with decreasing branch length, consistent with reduction in entanglement length and increase in tube diameter. This study contributes to the nanometer level insight into long-lived problems in viscoelastic responses of polymers.