Paper Number
SM26 

Session
Polymers Solutions, Melts and Blends

Title
Relating solvent dynamics to the extensional viscosity of entangled polymer solutions

Presentation Date and Time
October 22, 2019 (Tuesday) 4:35

Track / Room
Track 3 / Room 201

Authors (Click on name to view author profile)

  1. O'Connor, Thomas C. (Sandia National Laboratories, Harry S. Truman Fellow)
  2. Hopkins, Austin (Johns Hopkins University, Physics and Astronomy)
  3. Robbins, Mark O. (Johns Hopkins University, Physics and Astronomy)

Author and Affiliation Lines (in printed abstract book)
Thomas C. O'Connor1, Austin Hopkins2, and Mark O. Robbins2
1Harry S. Truman Fellow, Sandia National Laboratories, Albuquerque, NM; 2Physics and Astronomy, Johns Hopkins University, Baltimore, MD

Speaker / Presenter 
O'Connor, Thomas C.

Text of Abstract
Polymer melts and solutions with the same entanglement Z have similar linear viscoelasticity but can exhibit qualitatively different behavior during nonlinear extensional flow. A popular explanation is that chains in oriented melts experience less friction then chains immersed in unoriented solvent. However, new experiments (Shahid et al., Macromol., 2019) contradict this view, showing the high-rate viscosity of PS solutions is independent of the orientation of solvent. Here, we use molecular dynamics simulations to determine the effects of solvent on the nonlinear extension of entangled bead-spring solutions. Solutions with the same polymer concentration and Z, but varying solvent oligomer lengths are deformed to steady state in uniaxial extension flows for Rouse Weissenberg numbers from 0.1-25. All simulated solutions approach the same high-rate viscosity, independent of solvent orientation. Unlike experiments, simulations allow us to independently adjust polymer concentration, Ne, and Z. We leverage this to design melts with the same Ne and Z as solutions while maintaining the same monomer interactions. These melts show the same rate-dependence in viscosity as the solutions without any solvent. Our results imply that neither the presence nor the orientation of oligomer solvents is essential to produce the nonlinear trends in viscosity often seen in entangled solutions. Instead, we explain them as cross-over from a Newtonian limit to a high-rate limit for aligned chains.