But if you can create a surface where the water spreads out and forms a thin film, its perfect for anti-fogging, says Michael Rubner, a chemist at the Massachusetts Institute of Technology, US, whose team has developed the new anti-fog coating. The waters still there, but you cant see it.
Fog is caused when steam condenses on a cool surface and then forms minuscule water droplets due to the waters surface tension. Water molecules are more attracted to each other than to air molecules and form a spherical shape to maximise contact between water molecules, which leaves as few as possible exposed to the air.
But water is also attracted to glass, and if this attraction is enhanced, it can overcome the surface tension. Previous anti-fog coatings have capitalised on this using titanium dioxide surfaces which increase the attraction between the water and glass. This overcomes surface tension so the water spreads out in sheets.
However, these coatings first need to be charged by UV light which means they do not work for long in the dark. And they tend to stop working altogether after three months, says Yuri Lvov, a chemist at Louisiana Tech University in Ruston, US, who designed such a coating.
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