Universal consequences of the presence of excluded volume interactions in dilute polymer solutions undergoing shear flow

TL;DR

This paper investigates how excluded volume interactions influence the universal rheological behavior of dilute polymer solutions under shear flow, revealing increased shear thinning and altered chain alignment as solvent quality varies.

Contribution

It demonstrates that universal scaling functions and asymptotic behaviors are model-independent and predicts how excluded volume interactions affect polymer solution rheology.

Findings

Universal viscometric functions exhibit increased shear thinning with better solvent quality.

Power law scaling of viscometric functions in the excluded volume limit agrees with renormalization group results.

Excluded volume interactions weaken polymer chain alignment with flow direction.

Abstract

The role of solvent quality in determining the universal material properties of dilute polymer solutions undergoing steady simple shear flow is examined. A bead-spring chain representation of the polymer molecule is used, and the influence of solvent molecules on polymer conformations is modelled by a narrow Gaussian excluded volume potential that acts pair-wise between the beads of the chain. Brownian dynamics simulations data, acquired for chains of finite length, and extrapolated to the limit of infinite chain length, are shown to be model independent. This feature of the narrow Gaussian potential, which leads to results identical to a $\delta$-function repulsive potential, enables the prediction of both universal crossover scaling functions and asymptotic behavior in the excluded volume limit. Universal viscometric functions, obtained by this procedure, are found to exhibit increased shear thinning with increasing solvent quality. In the excluded volume limit, they are found to obey power law scaling with the characteristic shear rate $\beta$, in close agreement with previously obtained renormalization group results. The presence of excluded volume interactions is also shown to lead to a weakening of the alignment of the polymer chain with the flow direction.