Visualization study on the dynamic behavior of shear thinning droplets impacting superhydrophobic spheres

The surface and droplet characteristics significantly affect the dynamic of droplet impact on solid surfaces. In present work, a platform is utilized to experimentally study the dynamic behavior of shear thinning fluid droplets impacting superhydrophobic spheres, where the effects of different concentrations, Weber numbers (We), particle size ratios on droplets impact are studied. The results showed that on the superhydrophobic sphere, as the shear thinning droplet concentration increases, the diffusion diameter increases, and the contact time decreases. For the same curvature, the contact time between the droplet and the sphere decreases with the increase of the We. When the We reaches 75 or above, the contact time remains constant with an increase in the We. For various curvature conditions, the contact time increases as the curvature increasing. When the diameter ratio of the sphere to the droplet is $D_{\ast }\ge 6$, the maximum diffusion coefficient remains almost constant. However, when $D_{\ast }<6$, the maximum diffusion dimensionless diameter significantly increases as the particle size ratio decreases. More importantly, a theoretical model considering gravity effect is presented to predict the maximum dimensionless diameter of shear thinning droplets on superhydrophobic spheres according to energy conservation. The predicted results are rationally agreement with experiments with the deviation within ±10 %.