Thermodynamics of sustaining gases in the roughness of submerged superhydrophobic surfaces

摘要

Rough surfaces submerged in a liquid can remain almost dry if the liquid doesnot fully wet the roughness and gases are sustained in roughness grooves. Suchpartially dry surfaces can help reduce drag or enhance boiling. Gases sustainedin roughness grooves would be composed of air and the vapor phase of the liquiditself. The thermodynamics of sustaining vapor was considered in a prior work[Patankar, Soft Matter, 2010, 6:1613]. Here, the thermodynamics of sustaininggases (e.g. air) is considered. Governing equations are presented along with asolution methodology to determine a critical condition to sustain gases. Thecritical roughness scale to sustain gases is estimated for different degrees ofsaturation of gases dissolved in the liquid. It is shown that roughnessspacings of less than a micron are essential to sustain gases on surfacessubmerged in water at atmospheric pressure. This is consistent with priorempirical data.