Competition between shear and biaxial extensional viscous dissipation in the expansion dynamics of Newtonian and rheo-thinning liquid sheets

TL;DR

This paper investigates how shear and biaxial extensional viscous dissipation influence the expansion of liquid sheets from impacting drops, providing a predictive model for maximum expansion based on viscosity effects in Newtonian and viscoelastic fluids.

Contribution

It introduces a combined viscous dissipation approach to predict maximum sheet expansion, highlighting the dominance of extensional viscosity in viscoelastic fluids and validating it with experimental data.

Findings

Biaxial extensional and shear dissipation are comparable in Newtonian fluids.

Shear dissipation is negligible in supramolecular polymer solutions.

Biaxial extensional viscosity accurately predicts maximum expansion in viscoelastic liquids.

Abstract

When a drop of fluid hits a small solid target of comparable size, it expands radially until reaching a maximum diameter and subsequently recedes. In this work, we show that the expansion process of liquid sheets is controlled by a combination of shear (on the target) and biaxial extensional (in the air) deformations. We propose an approach toward a rational description of the phenomenon for Newtonian and viscoelastic fluids by evaluating the viscous dissipation due to shear and extensional deformations, yielding a prediction of the maximum expansion factor of the sheet as a function of the relevant viscosity. For Newtonian systems, biaxial extensional and shear viscous dissipation are of the same order of magnitude. On the contrary, for thinning solutions of supramolecular polymers, shear dissipation is negligible compared to biaxial extensional dissipation and the biaxial thinning extensional viscosity is the appropriate quantity to describe the maximum expansion of the sheets. Moreover, we show that the rate-dependent biaxial extensional viscosities deduced from drop impact experiments are in good quantitative agreement with previous experimental data and theoretical predictions for various viscoelastic liquids.