Paper Number
SM13 

Session
Polymers Solutions, Melts and Blends

Title
Examination of non-universalities in entangled polymer melts and solutions during the startup of steady shear flow

Presentation Date and Time
October 10, 2022 (Monday) 4:05

Track / Room
Track 2 / Sheraton 3

Authors (Click on name to view author profile)

  1. Becerra, Diego (Ohio State University, Chemical and Biomolecular Engineering)
  2. Córdoba, Andrés (University of Chicago, Molecular Engineering)
  3. Schieber, Jay D. (IIT, uCoSM)

Author and Affiliation Lines (in printed abstract book)
Diego Becerra1, Andrés Córdoba2 and Jay D. Schieber3
1Chemical and Biomolecular Engineering, Ohio State University, Columbus, OH; 2Molecular Engineering, University of Chicago, Chicago, IL; 3uCoSM, IIT, Chicago, IL 60616

Speaker / Presenter 
Córdoba, Andrés

Keywords
polymer melts

Text of Abstract
The possibility of nonuniversality during the inception of shear flow at large strain rates has recently been questioned, and hence it was examined using the discrete slip-link model (DSM). An expression for the Rouse relaxation time as a function of entanglement activity and number of Kuhn steps was found from a master curve of strain maxima, as predicted by the theory. DSM predicts only a very weak dependence of Rouse time on chemistry [Macromolecules 54, 8033–8042 (2021)]. This expression is shown to collapse all entangled polymer solution and melt data to universal behavior for the maximum shear stress and the strain at maximum stress. The transition of these quantities from strain-rate-free values to values that scale with dimensionless strain rate as 0.33 is shown to correspond to primitive path stretching. Furthermore, the scaling exponents for melt (0.1–0.15) and solution (0.2--0.3) in experimental data do not show the same scaling for steady-state shear stress, but the melts are in agreement with DSM (0.1). There is a small amount of data for the scaling of stress at undershoot, and strain at undershoot, which are predicted to scale as 0.1 and 0.33 for DSM, in agreement with melt data. Entangled solution data show greater scatter in exponents, which makes conclusions more difficult to draw, although they are not too different from melts. Remarkably, the existing molecular dynamics simulations disagree with each other, disagree with data, and with DSM.