Impact Dynamics of Non-Newtonian Droplets on Patterned Surfaces: Influence of Topography and Inclination

The fluids we come across in the automobile or health industries do not follow Newton’s law of viscosity. Broad applications of non-Newtonian fluids range in food, automobile, and biomedical industries. The impact dynamics of non-Newtonian drops on a topographically patterned surface are ubiquitous in nature. The constitutive law of the fluid and the surface morphologies have a pronounced effect on the post-impact dynamics. We delineate a combined effect of the surface morphology, impact velocity, and the inclination angle of the substrate. Our results showed that the drop undergoes a damped simple harmonic oscillatory motion over time. A transient competition between the kinetic, surface, and viscous energy dictates the overall dynamics of the drop. After impacting, the drop spreads to a maximum radius and forms a thin film due to inertial forces, while the surface tension and viscosity act as resisting forces. Surface tensions act as the driving force during the retraction of the film, and adhesion forces oppose the motion. The dynamic competition between inertia and surface tension forces gives rise to capillary waves, which disappear via viscous dissipation. Geometrical parameters and tilting angle modify the overall dynamics and alter the wetting phenomena. A sliding motion of the drop is also observed as the inclination of the basement exceeds a critical angle.