Dynamic characteristics of droplets' impact on solid surfaces with varied roughness

Probing into the process of droplets impacting solid surfaces and revealing their underlying behavioral characteristics is paramount across diverse fields. A high-speed camera capable of recording at 10,000 frames per second is utilized to capture the impact process of droplets on various rough surfaces. The effects of the droplets' properties, surface roughness, and surface wettability on the dynamic spread of droplets on solid surfaces are investigated. The research demonstrates that the addition of surfactants reduces the surface tension of droplets and dampens their vertical oscillations on surfaces, leading to decrease in the time required to achieve equilibrium. The increase in surface roughness leads to the decrease in droplet retraction degree and the decrease in maximum spreading coefficient. The surface wettability also influences the maximum spread coefficient and equilibrium time. The equations for the maximum spreading coefficient of the droplets on a solid surface with respect to the Weber number (We) and the revised capillary number (Ra*) are obtained by quantitative analysis.