The African Stenocara beetle has become mildly famous for using its wings to capture vapor molecules in the parched Namib Desert air and to herd them into a droplet that rolls into its mouth. Now two Massachusetts Institute of Technology professors have devised a material that mimics this action and goes a step further, which may lead to a range of long-anticipated products that manhandle fluids.
Chemical engineer Robert E. Cohen and materials scientist Michael F. Rubner seeded a polymer thin film with rows of silica nanoparticles and coated the surface with a fluorinated chemical that aggressively repels water. They then attached acid molecules to the nanoparticles, forming rows of nodes (like lights lining the sides of airport runways) that strongly attract water. Vapor molecules run off the hydrophobic runways and coalesce into droplets at the hydrophilic nodes. As the droplets grow, they fuse and run off in straight channels to be collected at the film's edge.