Individual and combined effects of roughness and wettability of surface on the collision dynamics

The experimental studies on the effect of surface roughness and wettability as independent factors on the dynamics of liquid droplet collisions with surfaces, using water as an example, were conducted. Dependencies of the rebound height of droplets on the arithmetic mean roughness height and contact time with surfaces were determined. Using experimental data on surface texture, a predictive mathematical simulation was conducted. The phase field method was applied to simulate the water droplet-surface interactions using surfaces with superhydrophobic properties and different textures. The arithmetic mean roughness heights varied within the range of 5–35 μm. The roll-off angle was found to serve as an indicator of the surface water-repellent effectiveness even at low Weber numbers (We < 25). Higher roll-off angles indicated a tendency for droplets to adhere, which suggests a reduction in the material's hydrophobicity. It was shown that the texture of a superhydrophobic surface significantly influences the critical We at which transitions occur between the following modes: rebound/partial rebound/rebound with separation-destruction. It was justified that for We less than 5 and greater than 120, the influence of surface properties on these processes diminishes. Parameter charts for interactions between droplets and surfaces were constructed. They allow to predict conditions under which significant individual and combined effects of wettability and surface roughness occur in scenarios relevant to practical applications.