Novel membrane reveals water molecules will bounce off a liquid surface
Consider the nearest water surface: a half-full glass on your desk, a puddle outside your window, or a lake across town. All of these surfaces represent liquid-vapor interfaces, where liquid meets air. Molecules of water vapor constantly collide with these liquid surfaces: Some make it through the surface and condense, while others simply bounce off. The probability that a vapor molecule will bounce, or reflect, off a liquid surface is a fundamental property of water, much like its boiling point. And yet, in the last century, there has been little agreement on the likelihood that a water molecule will bounce off the liquid surface. “When a water vapor molecule hits a surface, does it immediately go into the liquid? Or does it come off and hit again and again, then eventually go in?” says Rohit Karnik, an associate professor of mechanical engineering at MIT. “There’s a lot of controversy, and...