Model for the shear viscosity of suspensions of star polymers and other soft particles

TL;DR

This paper introduces a simple model that accurately predicts the viscosity of suspensions of soft particles like star polymers by incorporating particle softness into existing rigid sphere models, explaining experimental observations.

Contribution

A novel, straightforward model that accounts for particle softness in viscosity predictions of suspensions, extending rigid sphere models to soft particles.

Findings

Model accurately fits experimental data for star polymer suspensions.

Explains weak viscosity increase due to particle softness.

Uses Daoud-Cotton model for semi-dilute regimes.

Abstract

We propose a model to describe the concentration dependence of the viscosity of soft particles. We incorporate in a very simple way the softness of the particles into expressions originally developed for rigid spheres. This is done by introducing a concentration-dependent critical packing, which is the packing at which the suspension looses fluidity. The resultant expression reproduces with high accuracy the experimental results for suspensions of star polymers in good solvents. The model allows to explain a weak increase of the viscosity observed in the case of diblock copolymer stars suggesting that the reason for this peculiar behavior is mainly a consequence of the softness of the particles. In the semi-dilute regime, suspensions of star polymers are modeled using the Daoud-Cotton picture to complete the description in the whole concentration regime.