Simulating the Far-From-Equilibrium Dynamics and Elongational Rheology of Architecturally Diverse Polymer Melts*

Many industrial processes elongate polymer liquids at rates much faster than the molecular chain's characteristic relaxation times. These nonlinear elongation flows can strongly deform microscopic polymer conformations and drive dynamic transitions that produce large changes in polymer viscosity. Understanding how flow depends upon and drives such changes in polymer microstructure is essential for improving established and emerging fabrication methods like fiber spinning and 3D printing, and diversifying the applications of upcyclable chemistries. However, most microscopic understanding of these nonlinear flows has been drawn from indirect techniques that infer molecular dynamics from macroscopic rheology. This has begun to change with the recent development of new experimental and numerical simulation techniques that allow researchers to control, sustain, and microscopically probe polymer dynamics during strong elongational flows. Here, I’ll present molecular simulations for linear, star, and ring polymer melts and blends deformed in uniaxial elongational flow. In all three cases, coarse-grained molecular dynamics simulations reproduce the nonlinear rheology observed in extensional flow experiments and reveal the polymer dynamics and emergent chain topologies that underly each liquid's far-from-equilibrium behavior.