Tiny nature-inspired cavities that trap air can stop liquids from sticking to surfaces without the need for coatings.
An eco-friendly coating-free strategy has now been developed to make solid surfaces liquid repellent, which is crucial for the transportation of large quantities of liquids through pipes. Researchers from KAUST’s Water Desalination and Reuse Center have engineered nature-inspired surfaces that help to decrease frictional drag at the interface between liquid and pipe surface.
Piping networks are ubiquitous to many industrial processes ranging from the transport of crude and refined petroleum to irrigation and water desalination. However, frictional drag at the liquid–solid interface reduces the efficiency of these networks.
Conventional methods to reduce drag rely solely on chemical coatings, which generally consist of perfluorinated compounds. When applied to rough surfaces, these coatings tend to trap air at the liquid-solid interface, which reduces contact between the liquid and the solid surface. Consequently, this enhances the surface omniphobicity, or ability to repel both water- and oil-based liquids.
“But if the coatings get damaged, then you are in trouble,” says team leader, Himanshu Mishra, noting that coatings break down under abrasive and elevated temperature conditions.
So Mishra’s team developed microtextured surfaces that do not require coatings to trap air when immersed in wetting liquids by imitating the omniphobic skins of springtails, or Collembola, which are insect-like organisms found in moist soils. The researchers carved arrays of microscopic cavities with mushroom-shaped edges, called doubly reentrant (DRC), on smooth silica surfaces.
“Through the DRC architecture, we could entrap air under wetting liquids for extended periods without using coatings,” says co-author Sankara Arunachalam. Unlike simple cylindrical cavities, which were filled in less than 0.1 seconds on immersion in the solvent hexadecane, the biomimetic cavities retained the trapped air beyond 10,000,000 seconds.
To learn more about the long-term entrapment of air, the researchers systematically compared the wetting behavior of circular, square and hexagonal DRCs. They found that circular DRCs were the best at sustaining the trapped air.
thumbnail courtesy of discovery.kaust.edu.sa