Paper Number
SM11 

Session
Polymers Solutions, Melts, and Blends

Title
Entanglement kinetics during interrupted orthogonal shear flow

Presentation Date and Time
October 11, 2021 (Monday) 4:10

Track / Room
Track 1 / Ballroom 5

Authors (Click on name to view author profile)

  1. Olmsted, Peter D. (Georgetown University)
  2. Cuhna, Marco Galvani (University of Pennysylvania, Department of Physics)
  3. Robbins, Mark O. (Johns Hopkins University, Department of Physics)

Author and Affiliation Lines (in printed abstract book)
Peter D. Olmsted1, Marco Galvani Cuhna2 and Mark O. Robbins3
1Georgetown University, Washington, DC 20057-0004; 2Department of Physics, University of Pennysylvania, Philadelphia, PA 19104; 3Department of Physics, Johns Hopkins University, Baltimore, MD

Speaker / Presenter 
Olmsted, Peter D.

Keywords
theoretical methods; computational methods; additive manufacturing; flow-induced instabilities; polymer melts; polymer solutions

Text of Abstract
Both entangled and unentangled polymer melts exhibit stress overshoots when subject to shearing flow. The size of the overshoot depends on the applied shear rate and is related to relaxation mechanisms such as reptation, chain stretch and convective constraint release. Previous experimental work shows that melts subjected to interrupted shear flows exhibit a smaller overshoot when sheared after some relaxation. The time scale for recovery of the maxima is about the timescale for relaxation of the stress for unentangled chains but is significantly longer for entangled chains. This is attributed to changes in the entanglement structure of the melt due to the applied flow, and the Rolie-Poly model (among others) has been used to show this behavior is consistent with tube theory. Here, we show results of molecular dynamics simulations of interrupted shear of polymer melts where the shear flow after the relaxation stage is orthogonal to the original applied flow. We observe that the size of the stress overshoot is larger than predictions by the Rolie-Poly model, and larger than observed during a second shear in the same direction as the original for the same relaxation time. Differences in maxima are also observed for overshoots in the first normal stress and chain end-to-end distance, as well as in minima for undershoots in the second normal stress and in the number of entanglements per chain as measured with standard computational tools.