Sustaining dry surfaces under water

TL;DR

This paper investigates how to keep immersed rough surfaces dry by analyzing the critical roughness scale that sustains vapor and trapped gases, supported by theory, simulations, and experiments.

Contribution

It introduces a new understanding of the roughness scale needed to maintain dry surfaces underwater by considering vapor and gas retention mechanisms.

Findings

Identifies the critical roughness scale for sustaining vapor and gas phases.

Theoretical predictions align with molecular dynamics simulations.

Experimental validation confirms the importance of roughness scale in surface dryness.

Abstract

Rough surfaces immersed under water remain practically dry if the liquid-solid contact is on roughness peaks, while the roughness valleys are filled with gas. Mechanisms that prevent water from invading the valleys are well studied. However, to remain practically dry under water, additional mechanisms need consideration. This is because trapped gas (e.g. air) in the roughness valleys can dissolve into the water pool, leading to invasion. Additionally, water vapor can also occupy the roughness valleys of immersed surfaces. If water vapor condenses, that too leads to invasion. These effects have not been investigated, and are critically important to maintain surfaces dry under water. In this work, we identify the critical roughness scale below which it is possible to sustain the vapor phase of water and/or trapped gases in roughness valleys - thus keeping the immersed surface dry. Theoretical predictions are consistent with molecular dynamics simulations and experiments.