Rapid wetting of shear-thinning fluids

TL;DR

This study combines experiments and simulations to compare the rapid spreading behaviors of shear-thinning and Newtonian fluids, revealing that shear-thinning fluids spread similarly to water initially, with viscosity influencing later stages.

Contribution

It provides new insights into the initial wetting dynamics of shear-thinning fluids, showing that their early spreading is unaffected by polymer concentration, unlike Newtonian fluids.

Findings

Shear-thinning solutions spread like water in the first millisecond.

Glycerol solutions show slower spreading with higher glycerol concentration.

Contact-line friction increases with glycerol but not with polymer concentration.

Abstract

Using experiments and numerical simulations, we investigate the spontaneous spreading of droplets of aqueous glycerol (Newtonian) and aqueous polymer (shear-thinning) solutions on smooth surfaces. We find that in the first millisecond the spreading of the shear-thinning solutions is identical to the spreading of water, regardless of the polymer concentration. In contrast, aqueous glycerol solutions show a different behavior, namely, significantly slower spreading rate than water. In the initial rapid spreading phase, the dominating forces that can resist the wetting are inertial forces and contact-line friction. For the glycerol solutions, an increase in glycerol concentration effectively increases the contact-line friction, resulting in increased resistance to wetting. For the polymeric solutions, however, an increase in polymer concentration does not modify contact-line friction. As a consequence, the energy dissipation at the contact line can not be controlled by varying the amount of additives for shear-thinning fluids. The reduction of the spreading rate of shear-thinning fluids on smooth surfaces in the rapid wetting regime can only be achieved by increasing solvent viscosity. Our results have implications for phase-change applications where the control of the rapid spreading rate is central, such as anti-icing and soldering