Impact of capillary drops of complex fluids on a solid surface

Abstract

The drop impact on a solid surface is studied in the context of complex fluids that exhibit viscoplastic, viscoelastic, and thixotropic behavior. The effects of rheology and surface tension are investigated for a range of corresponding dimensionless numbers associated with each phenomenon. Two usual quantities are employed to understand the drop dynamics, namely, the maximum spreading diameter and the time the drop remains in contact with the solid. Another result is the drop shape evolution, captured by displaying selected instants. The first part of the work is dedicated to examine the influence of capillary effects for more real fluids, in the present case, solutions of Carbopol, kaolin, and bentonite whose mechanical properties are taken from experimental measurements reported in the literature. In the second part, we conduct parametric studies varying the dimensionless numbers that govern the problem. We have shown that the influence of surface tension in yield stress materials is less significant and can be negligible when real parameters are input in the model. On the other hand, Newtonian and viscoelastic fluids are more susceptible to surface tension effects. This quantity tends to decrease maximum spreading diameter and decrease contact time due to its resistance in the spreading stage. While inertia, elasticity, and plastic effects favor the drop to spread and to increase its contact time with the solid substrate, a more thixotropic behavior leads to the opposite trend. Published under license by AIP Publishing.