Effect of stretching-induced changes in hydrodynamic screening on   coil-stretch hysteresis of unentangled polymer solutions
  Extensional rheometry and Brownian Dynamics simulations of flexible polymer solutions confirm predictions based on blob concepts that coil--stretch hysteresis in extensional flows increases with concentration, reaching a maximum at the critical overlap concentration $c^\ast$ before progressively vanishing in the semidilute regime. These observations demonstrate that chain stretching strengthens intermolecular hydrodynamic screening in dilute solutions, but weakens it in semidilute solutions. Flow can thus strongly modify the concentration dependence of viscoelastic properties of polymer solutions. 
Ranganathan Prabhakar, Chandi Sasmal, Duc At Nguyen, Tam Sridhar, J.   Ravi Prakash
cond-mat.soft