Superhydrophilicity refers to the phenomenon of excesshydrophilicity, or attraction to water; in superhydrophilic materials, thecontact angle of water is equal to zero degrees. This effect was discovered in 1995 by the Research Institute ofToto Ltd. fortitanium dioxide irradiated bysunlight. Under light irradiation, water dropped onto titanium dioxide forms nocontact angle (almost 0 degrees).[1]
Superhydrophilic material has various advantages. For example, it can defog glass, and it can also enable oil spots to be swept away easily with water. Such materials are already commercialized as door mirrors for cars, coatings for buildings,self-cleaning glass, etc.[citation needed]
Several mechanisms of this superhydrophilicity have been proposed by researchers.[citation needed] One is the change of the surface structure to ametastable structure, and another is cleaning the surface by thephotodecomposition of dirt such asorganic compoundsadsorbed on the surface, after either of which water molecules can adsorb to the surface. The mechanism is still controversial, and it is too soon to decide which suggestion is correct. To decide, atomic scale measurements and other studies will be necessary.[citation needed]