Uniaxial elongational flow of entangled, associating linear polymer melts

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 their 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 varying from 1k_BT to 10k_BT, using molecular dynamics simulations. Chains of length 100 to 800 beads/chain are studied, covering the range from weakly to highly entangled chains. We find that cluster size increases with increasing interaction between the associating beads. Under flow, 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 baring strong associating group even at high extension rates, the clusters do not fully break up and only a fraction of chains is fully stretched. Results from constant pressure and constant volume simulations are compared.