Compression-thinning behavior of bubble suspensions

TL;DR

This paper reveals a novel compression-thinning behavior in bubble suspensions, showing shear viscosity decreases under compression due to bubble surface shrinking, with a theoretical model incorporating shear and dilatation effects.

Contribution

It introduces the first observation of compression-thinning in bubble suspensions and proposes a constitutive equation accounting for both shear and dilatation effects.

Findings

Bubble suspensions exhibit shear-thinning under shear deformation.

Compression reduces shear viscosity due to bubble surface shrinking.

Theoretical model highlights the significance of dilatation effects on viscosity.

Abstract

Rheology of bubble suspensions is critical for the prediction and control of bubbly flows in a wide range of industrial processes. It is well-known that the bubble suspension exhibits a shear-thinning behavior due to the bubble shape deformation under pure shear, but how the shear rheology response to dilatation remains unexplored. Here, we report a compression-thinning behavior that the bubble suspension exhibits a decreasing shear viscosity upon compressing. This peculiar rheological behavior is microscopically due to that a shrinking bubble surface effectively weakens the flow resistance of the surrounding liquid. We theoretically propose a constitutive equation for dilute bubble suspensions considering both shear and dilatation effects, and demonstrate that the contribution of dilatation effect on the shear viscosity can be significant at a changing pressure.