Nonlinear uniaxial elongational flow of entangled, associating linear polymer melts: MD Simulation study

The response of polymers to uniaxial elongational flow affects the structure of polymers which is critical for their processing.  The more structured the polymer, the more complex its response becomes. Here we probe the effects of uniaxial elongational flow on entangled, linear polymer melts.  The polymers are depicted by a bead spring model with 5% randomly incorporated interacting associating beads, as the interaction strengths vary from 1kBT to 10kBT, using molecular dynamics simulations.  Chain lengths of 400 beads/chain are studied, covering the range from weak to highly entangled chains. We find that cluster size increases with increasing interaction between the associating beads. Underflow, these clusters continuously break and reform as the chains stretch.As the sticker strength increases, the distribution of end-to-end distances becomes heterogeneous.  Surprisingly, for polymers bearing strong associating groups, even at high extension rates, the clusters do not fully break up, and only a fraction of chains are fully stretched. Results from constant pressure and constant volume simulations are compared. Funding: NSF  DMR 1905407