Dynamic Behavior of Non-Newtonian Droplets Impinging on Solid Surfaces

Abstract

This article illustrates the spreading and receding characteristics of non-Newtonian droplets impinging on solid surfaces at different Weber numbers. A xanthan gum solution was used to generate non-Newtonian droplets. From digital images captured using a high speed camera, spreading diameters and dynamic contact angles (DCA) were measured during the impact process. Depending on impact velocity, distinct differences in spreading and receding motions were found between Newtonian and non-Newtonian droplets, which were highly associated with viscous energy dissipation. The maximum spreading diameters for Newtonian and non-Newtonian droplets were nearly the same, but a much slower receding motion was observed for non-Newtonian droplets because of the shear-thinning effect. Moreover, a rapid decrease of DCA in the spreading regime was observed for both non-Newtonian and Newtonian droplets, indicating that the inertial force became dominant. By contrast, measured DCAs for non-Newtonian fluid droplets in the receding regime were larger than those for Newtonian fluid droplets, demonstrating that cohesive surface forces were more dominant than inertial forces in this regime.