Entanglement Topology of Ring-Linear Polymer Blends

The topological constraints of no free ends force non-concatenated ring polymers in a melt to form compact loopy globular conformations. The closed-loop structure of ring polymers also enables them to be threaded by linear polymers in ring/linear blends. This threading of the rings by linear chains leads to several interesting phenomena including a non-monotonic increase in the shear viscosity as a function of ring fraction and transition in the stress relaxation from a power law decay for large ring fractions to a plateau as the fraction of rings decreases. In this talk, I will present results from equilibrium and non-equilibrium molecular dynamics simulations of the equilibrium dynamics, entanglement topology, and nonlinear extensional rheology of ring/linear polymer blends, systematically varying the fraction of rings and the ratio of ring and linear chain lengths. The relaxation time of the rings is found to dependent strongly on the linear chain length as the rings cannot relax until the linear chains threading them reptate away. Primitive path analysis is used to visualize and quantify the structure of the composite ring-linear entanglement network and degree of threading. Under uniaxial extensional flow, there is an initial stress overshoot, which is due to overstretching of the rings, followed by a recoil of the rings as they unthread from the linear chain. The relaxation times to re-thread the linear chains into the rings after cessation of flow is followed and related to the equilibrium relaxation times for the ring and linear chains for varying linear chain length.

In collaboration with Thomas C. O’Connor and Ting Ge