Gradient Nonwettability Controls Water-Film Flowing Features

Abstract

The flow of the water film on solid surface depended on the film Reynolds number and wind speed. Moreover, environmental factors had an impact on the flow process. This study explored how surface wettability impacts the stability and detachment of water film under varying conditions. Superhydrophobic surface played a critical role in speeding up the detachment of water film, especially under conditions of strong wind and specific flow dynamics, such as a wind speed of 19 m/s and a Reynolds number of 83. The efficiency in water removal was due to a combination of forces: capillary action, which pulls the water into smaller areas, reduced surface tension, and decreased adhesion between the liquid and surface. These factors worked together to shrink the area of contact, allowing the film to break and detach more easily. The findings suggested that enhancing nonwettability can improve water removal efficiency, with potential applications in fields like aerospace. Furthermore, additional trials across varying wind speeds and Reynolds numbers consistently supported the superior performance of superhydrophobic surface in driving rapid water-film detachment. To advance this effect, a gradient nonwetting surface was introduced, specifically engineered within the superhydrophobic regime, to amplify the velocity of film separation. This design innovation leveraged variations in surface energy across the gradient, which fostered directional waterfilm movement and accelerated detachment. A comprehensive analysis of the underlying physical mechanisms further elucidated its potential in enhancing water-shedding applications across a range of environmental conditions.