Take a hot shower and the chances are that the bathroom mirror will mist up. Glasses and camera lenses can also suffer in humid conditions. And it can be dangerous when a car’s windscreen clouds over. Various methods, including sprays, materials and heating, have been used with varying degrees of success to deal with the problem. Now a Chinese team has come up with a new idea.via The Economist
Junhui He of the Chinese Academy of Sciences, Beijing, and his colleagues have created a cheap anti-mist coating. They estimate one square metre of glass will cost only a few cents to treat.
Glass mists up because of sudden condensation when warm, humid air comes into contact with a cold surface. Water vapour condenses to form thousands of tiny water droplets which scatter light. Dr He and his colleagues knew that when certain nanoparticles (which have diameters of only a few billionths of a metre), are spread over glass they break the surface tension of the droplets as they try to form. The result is a thin, transparent film of water which, unlike droplets, does not scatter light.
But what size and shape of nanoparticles is most effective and can be produced cheaply? Dr He’s team experimented with different shapes and found a simple one-step method using polystyrene spheres treated with oxygen and then coated with silica to build raspberry-like shapes. These shapes have proved to be the most effective in preventing a surface from misting over. Dr He and his colleagues hope to commercialise the process quickly.