A bouncing and rotating drop after oblique impact on Lubricant-Impregnated surfaces

While perfectly water-repellent surfaces, such as superhydrophobic surfaces, always repel water drops after contact, the drops can either stick to or bounce off lubricant-impregnated surfaces (LISs) depending on the impact conditions. This study investigates the rebound behavior of water drops on LIS, highlighting how this phenomenon significantly depends on both the viscosity of the lubricant and the obliqueness of the surface. Both the lubricant viscosity and surface obliqueness contribute to an increase in dissipation: an increase in lubricant viscosity directly increases the viscous force, and increased surface obliqueness causes the drop to slide on a viscous liquid, resulting in increased dissipation energy. Throughout the study, the dissipation energy attributed to sliding and inelastic collision is addressed. Additionally, we identify an intriguing rotational behavior of drops post-rebound. The direction of rotation varies with the viscosity of the LIS, impact velocity, and surface obliqueness. Numerical simulations demonstrate that this rotation direction is determined by the front and rear velocities of the drop, which is affected by the dynamic advancing and receding contact angles.