Nonlinear Elongation Flows Effects on Aggregation in Associating Polymer Melts

Incorporating associating groups into polymer melts strongly effects both chain mobility and viscoelastic response. Associating groups form nanoscale clusters whose size depends on the competition of associating group interactions and chain conformational entropy. Here, we use molecular dynamics (MD) simulations of bead-spring chains to identify how associating groups alter the structure and dynamics of linear polymer melts in uniaxial elongation flows. Associating groups whose interaction strength is varied from 1-20 k_BT are randomly included in the backbone of the chains. The cluster sizes of associating groups increase with increasing association strength, and a corresponding increase in an elongational stress overshoot and the steady-state viscosity. For weak association and small clusters, chains first elongate until tension is sufficient to break up the small associating clusters. As the association strength increases, chain elongation and cluster breakup occur simultaneously and are insensitive to strain rate, mimicking solid-like behavior. For association strength ≥ 10 k_BT, clusters act like stiff inclusions and the system fails as voids are formed during elongation.