Paper Number
SM3
Session
Polymers Solutions, Melts, and Blends
Title
A thermodynamically consistent model of polymer disentanglement under flow
Presentation Date and Time
October 11, 2021 (Monday) 10:40
Track / Room
Track 1 / Ballroom 5
Authors
- Benjamin, Dolata E. (Georgetown University, Department of Physics)
- Olmsted, Peter D. (Georgetown University)
Author and Affiliation Lines
Dolata E. Benjamin and Peter D. Olmsted
Department of Physics, Georgetown University, Washington, DC 20007
Speaker / Presenter
Benjamin, Dolata E.
Keywords
theoretical methods; non-Newtonian fluids; polymer melts
Text of Abstract
We formulate a thermodynamically consistent constitutive equation modeling the stretch, orientation, and disentanglement of a polymer melt under flow. Most prior constitutive equations do not explicitly track the evolution of entanglements, rendering them unable to model physical phenomena such as the diffusion of entanglements across the interface during the welding of polymer filaments in additive manufacturing processes. We overcome this limitation by developing explicit coupled evolution equations for the tube conformation and number of entanglements. The conformation kinetic equation is inspired by the Rolie-Poly equation, and accounts for reptation, retraction and convective constraint release. The evolution equation for entanglements contains terms governing shear-induced disentanglement and re-entanglement via reptation. The shear-induced disentanglement is obtained by casting the Ianniruberto and Marrucci disentanglement mechanism into a thermodynamically consistent form. Prior theories assumed that the melt will re-entangle on the reptation time. In contrast, we obtain the re-entanglement mechanism by computing the random walk statistics of a chain in a fixed network of entanglements. We find that the melt will re-entangle faster at the chain ends than the center, leading to a re-entanglement time scale that is shorter than the reptation time. Model predictions for the stress and entanglement evolution are in good agreement with measurements from molecular dynamics simulations, and the computed re-entanglement time is consistent with structural measurements from those same simulations.