(306h) Nonequilibrium Molecular Dynamics Simulations of Entangled Polymer Solutions Undergoing Planar Elongational Flows

Experiments have shown that concentrated solutions of polymer chains in small molecule solvents exhibit different flow dynamics when subject to elongational flows from polymer melts and polymer solutions that use short chain oligomers as the solvent. This difference has been attributed to the monomeric friction reduction induced by the anisotropic environment around the polymer chains at high extension rates that occur in polymer melts and polymer solutions that which oligomeric solvents. Molecular simulation of these liquids offers a complementary perspective of individual molecule dynamics under flow.

In this work, we performed nonequilibrium molecular dynamics (NEMD) simulations of entangled linear polyethylene solutions subject to planar elongational flows. Through this study, we investigate how flow dynamics is affected by the structure of the solvent and its interaction with polymer molecules. To achieve this, we used benzene as a small molecule solvent and C₁₆H₃₂ as an oligomeric solvent in two different sets of simulations. Rheological, structural, and topological (entanglement network) properties of the systems are studied as functions of extension rate. Specifically, segmental orientation and stretch of polymer molecules, as well as solvent oligomers, are examined within a wide range of Weissenberg numbers. We will also discuss steady state in elongational flows from a molecular perspective.