Paper Number
PO64 

Session
Poster Session

Title
Dynamics of entangled linear polymers at fast deformations: Influence of matrix viscoelasticity

Presentation Date and Time
October 13, 2021 (Wednesday) 6:30

Track / Room
Poster Session / Ballroom 1-2-3-4

Authors (Click on name to view author profile)

  1. Taghipour, Hamid (Univeriste catholique de Louvain, Bio and Soft Matter - IMCN)
  2. Hawke, Laurence (Univeriste catholique de Louvain, Bio and Soft Matter - IMCN)
  3. Vlassopoulos, Dimitris (IESL-FORTH and University of Crete)
  4. van Ruymbeke, Evelyne (Univeriste catholique de Louvain, Bio and Soft Matter - IMCN)

Author and Affiliation Lines (in printed abstract book)
Hamid Taghipour1, Laurence Hawke1, Dimitris Vlassopoulos2 and Evelyne van Ruymbeke1
1Bio and Soft Matter - IMCN, Univeriste catholique de Louvain, Louvain-la-Neuve 1348, Belgium; 2IESL-FORTH and University of Crete, Heraklion 71110, Greece

Speaker / Presenter 
Taghipour, Hamid

Keywords
flow-induced instabilities; polymer blends; polymer melts; polymer solutions

Text of Abstract
To deeply understand the nonlinear viscoelasticity of linear entangled chains we performed start-up shear experiments on four diluted melts and four binary blends of long polystyrene chains (PS 820kg/mol) with varying the concentration and molar mass of the matrix chains. Similarly to published experimental results, we find that in the elastic regime of deformation (i.e., at γ`τR (M)≫1) there is a fractional power-law scaling of the transient viscosity maximum vs the shear rate. We also find that the steady-state viscosity exhibits stronger strain-softening behavior as the entanglement density increases, which can eventually lead to macroscopic shear-banding. Regarding the Cox-Merz rule validity we find that, within experimental error, it is confirmed with the exception of two bidisperse blends having high molecular weight matrices. We attribute this failure to possible edge instability and fracture. Our experimental findings are compared against a nonlinear version of the Time Marching Algorithm (TMA) that couples the dynamics of orientation, stretch and constranit release (CR). The nonlinear TMA does a reasonable quantitative job in describing the nonlinear shear steady-state data, provided that the contribution of the matrix (short chains) to the overall polymer stress is accounted for. This work identifies future directions to fully predict the different relaxation dynamics under transient flow.