Shear thinning in dilute and semidilute solutions of polystyrene and DNA

TL;DR

This study investigates shear thinning behavior in dilute and semidilute DNA and polystyrene solutions, revealing universal patterns when using appropriate relaxation times, and compares experimental viscosity data across different regimes and conditions.

Contribution

It introduces a universal framework for understanding shear thinning in polymer solutions by employing a concentration-dependent correlation blob relaxation time.

Findings

Master plots are independent of temperature and concentration within regimes.

Using a correlation blob relaxation time reveals universal shear thinning behavior.

Shear rate dependence varies with the choice of relaxation time.

Abstract

The viscosity of dilute and semidilute unentangled DNA solutions, in steady simple shear flow, has been measured across a range of temperatures and concentrations. For polystyrene solutions, measurements of viscosity have been carried out in the semidilute unentangled regime, while results of prior experimental measurements in the dilute regime have been used for the purpose of data analysis, and for comparison with the behaviour of DNA solutions. Interpretation of the shear rate dependence of viscosity in terms of suitably defined non-dimensional variables, is shown to lead to master plots, independent of temperature and concentration, in each of the two concentration regimes. In the case of semidilute unentangled solutions, defining the Weissenberg number in terms of a concentration dependent large scale relaxation time is found not to lead to data collapse across different concentrations. On the other hand, the use of an alternative relaxation time, with the concentration dependence of a single correlation blob, suggests the existence of universal shear thinning behaviour at large shear rates.