Superhydrophilicity refers to the phenomenon of excess
hydrophilicity, or attraction to water; in superhydrophilic materials, the
contact angle of water is equal to zero degrees. This effect was discovered in 1995 by the Research Institute of
Toto Ltd.
, stylized as TOTO, previously known as Toyo Toki, is a Japanese multinational toilet manufacturer which is known for manufacturing the Washlet (as well as the Warmlet and similar products). TOTO was founded in 1917. The company is based in Ki ...
for
titanium dioxide
Titanium dioxide, also known as titanium(IV) oxide or titania , is the inorganic compound with the chemical formula . When used as a pigment, it is called titanium white, Pigment White 6 (PW6), or CI 77891. It is a white solid that is insolubl ...
irradiated by
sunlight
Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light. On Earth, sunlight is scattered and filtered through Earth's atmosphere, and is obvious as daylight when t ...
. Under light irradiation, water dropped onto titanium dioxide forms no
contact angle (almost 0 degrees).
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 Self-cleaning glass is a specific type of glass with a surface that keeps itself free of dirt and grime.
The field of self-cleaning coatings on glass is divided into two categories: hydrophobic and hydrophilic.
These two types of coating both clea ...
, etc.
Several mechanisms of this superhydrophilicity have been proposed by researchers. One is the change of the surface structure to a
metastable structure, and another is cleaning the surface by the
photodecomposition
Photodissociation, photolysis, photodecomposition, or photofragmentation is a chemical reaction in which molecules of a chemical compound are broken down by photons. It is defined as the interaction of one or more photons with one target molecule. ...
of dirt such as
organic compounds
adsorbed 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.
See also
*
Superhydrophobicity
Ultrahydrophobic (or superhydrophobic) surfaces are highly hydrophobic, i.e., extremely difficult to wet. The contact angles of a water droplet on an ultrahydrophobic material exceed 150°. This is also referred to as the lotus effect, after the ...
, the opposite phenomenon
References
Further reading
*{{cite journal , last1=Kommireddy , first1=Dinesh S. , last2=Patel , first2=Amish A. , last3=Shutava , first3=Tatsiana G. , last4=Mills , first4=David K. , last5=Lvov , first5=Yuri M. , title=Layer-by-Layer Assembly of TiO2 Nanoparticles for Stable Hydrophilic Biocompatible Coatings , journal=Journal of Nanoscience and Nanotechnology , date=1 July 2005 , volume=5 , issue=7 , pages=1081–1087 , doi=10.1166/jnn.2005.149 , pmid=16108431
Chemical properties
Surface science