Wrinkling Teflon creates a superhydrophobic surface

Superhydrophobic coatings that make water droplets dance and roll off a surface have been proposed for applications such as self-cleaning cars, buildings, and food-processing equipment. Chiara Neto of the University of Sydney and colleagues have devised a method for creating a more durable type of one of these coatings by combining slippery Teflon (polytetrafluoroethylene) and a heat-shrinkable plastic (ACS Appl. Mater. Interfaces 2016, DOI: 10.1021/acsami.5b12165). The scientists spin-coated a Teflon solution onto two types of shrinkable plastic: PolyShrink, a polystyrene material similar to that found in the children’s craft toy Shrinky Dinks, and a commercial polyolefin shrink-wrap. When heated, each type of polymer contracts, and the tightly bonded Teflon layer crinkles. The surface structure—decorated with nanometer-scale wrinkles on top of folds a few micrometers across—traps pockets of air and prevents the surface from getting wet. A combination of polyolefin coated with a 10-nm-thick layer of Teflon repelled water most effectively, inducing droplets to bead up to a measured contact angle of 172° so that they barely touch the surface. What’s more, the superhydrophobic coating retains its water repellency even when scratched.