There are two ways to create a hydrophobic material: You either coat it with some kind of wax (oil, grease, or some other special, hydrophobic substance); or you use nanoengineering to create a special, nanopatterned textured surface.
These nanopatterns, which are hydrophobic, take the form of little bumps or posts that are around 10 micrometers (10 micron, 10,000 nanometers) across. This kind of hydrophobic material is fairly well understood.
The MIT breakthrough being discussed today starts with a nanopatterned hydrophobic material — and then coats it in a very fine layer of lubricant, massively increasing its hydrophobicity. It turns out that the small gaps between the bumps/posts are capable of exerting just enough capillary force to hold an oil lubricant in place.
The scientists simply had to dunk the nanopatterned material into a vat of lubricant, pull it out, and the lubricant remains fixed in the material.
The nanopattern, plus the lubricant, results in a material that is 10,000 times more hybrophobic than the non-lubricated version. The pits are so small that it takes just half a teaspoon of lubricant to cover a square yard (0.8sqm) of the material. “Drops can glide on the surface,” Kripa Varanasi, the lead researcher, says. “These are just crazy velocities.”