King Abdullah University of Science and Technology (KAUST) scientists have developed an inexpensive green process that enables common materials to become liquid repellent.
The proposed method which is been inspired by springtails, a desert insect, could have far reaching implications in diverse applications such as underwater drag reduction and antifouling.
Surface liquid repellent is used in a range of industrial processes from reducing biofouling and underwater drag to membrane distillation, waterproofing and oil-water separation.
Producing such a veneer generally relies on applying perfluorinated coatings; however, these degrade under harsh physical and chemical environments, increasing costs and both health and environmental impacts and limiting their use.
Now Himanshu Mishra and colleagues from the KAUST Water Desalination and Reuse Center have sought inspiration from nature to make conventional materials, such as plastics and metals, omniphobic.
The researchers first tested microtextures comprising doubly reentrant pillars: they were inspired by a US-based research team who, in 2014, demonstrated these pillars exhibited unprecedented omniphobicity in air, even when the materials were intrinsically wetting.
The team confirmed that intrinsically wetting surfaces with doubly reentrant micropillars do indeed exhibit omniphobicity in air, but they also found that it was catastrophically lost in the presence of localized physical defects or damage or upon immersion in wetting liquids.
“These were serious limitations because real surfaces get damaged during use,” said Mishra. “This inspired us to look to nature and investigate the skins of springtails.”
Patterns on the skin of springtails – tiny soil-dwelling insects that live in moist conditions – exploit surface textures that contain doubly reentrant cavities, keeping them dry. By using photolithography and dry-etching tools at the KAUST Nanofabrication Core Lab, the researchers recreated these doubly reentrant microcavities on silica surfaces.
Taking advantage of the doubly reentrant features showed that the microcavities trapped air and prevented penetration of liquids, even under elevated pressures.
In addition, their compartmentalized nature prevented any loss of omniphobicity in the presence of localized damage or defects or upon immersion in wetting liquids.
Image credits and content: Ref 1., American Chemical Society/Ivan Gromicho/KAUST