Thursday, September 25, 2008
2008 R&D 100 Winner
Waxy spherical protrusions on the surface of the Lotus leaf force water droplets to assume a 150° or greater contact angle, allowing them to easily roll away. The patterned carapace of the Namib Sternocara Desert beetle nucleates water drops during fogs, which then roll toward its mouth for drinkinig. Like the Lotus and the desert beetle, the Superhydrophobic Coating from Sandia National Laboratories, Albuquerque, N.M., adopts a specialized surface geometry to manipulate the molecular tendencies of water.
The surface is a sol-gel coating that can be readily applied to surfaces—including optically transparent materials—by way of spray, dip, or spin methods. Unlike conventional coating systems, which shrink continuously during drying to produce low-porosity films, this coating springs back to a lower density state during the final stage of drying. The resulting structure, a silicon dioxide surface decorated with hydrophobic ligands, is highly porous, creating the nanoscale roughness necessary for the superhydrophobic effect. The coating functions up to 450°C, and water droplets on the surface are measured to have a 172° contact angle, forming a nearly perfect sphere.
Technology
Coating
Developer
Sandia National Laboratories
