The trick for keeping a surface dry comes down to the degree of ‘roughness’. The first step in the research project was to examine different types of surfaces and select those what were the least smooth. After different surfaces were submerged in water, it was found that the ‘valleys’ – a term for the gap between grooves in the surface that give a material its rough hue – needed to be less than one micron in width (a micron is one billionth of a meter, in other words very tiny indeed.)
The valleys allow pockets of vapor to be held in them, which prevent water from contacting with the surface material. This is by deflecting away water molecules. The vapor or gas is formed through underwater evaporation or effervescence. This process is similar to how certain insects are able to skate across water without getting wet. A similar phenomenon occurs with the lotus flower, when rain falls on the petals of the flower it simply rolls off. The scientific name for what is happening is “superhydrophobicity.”
The successful surfaces used for the study included bespoke polymers, zinc oxide nanorods, silicon nanograss, silicon microposts, silicon microgrooves, and silicon nanowire forests.
The practical uses for such a surface include developing anti-fouling surfaces for shipping and new pipe coatings for oil and gas, which would lead to lower drag.
The research was performed by engineers at Northwestern University. The research has been published in the journal Scientific Reports; the paper is headed “Sustaining Dry Surfaces Under Water.”
