chemistry, hydrophobicity (from the combining form of water in Attic Greek"hydro-" and for fear "phobos") refers to the physical property of a molecule(known as a hydrophobe) that is repelled from a mass of water[Aryeh Ben-Na'im "Hydrophobic Interaction" Plenum Press, New York (ISBN 0-306-40222-X)] .
Hydrophobic molecules tend to be
non-polarand thus prefer other neutral molecules and nonpolar solvents. Hydrophobic molecules in water often cluster together forming micelles. Water on hydrophobic surfaces will exhibit a high contact angle.
Examples of hydrophobic
moleculesinclude the alkanes, oils, fats, and greasy substances in general. Hydrophobic materials are used for oil removal from water, the management of oil spills, and chemical separation processes to remove non-polar from polar compounds.
Hydrophobic is often used interchangeably with
lipophilic, "fat loving." However, the two terms are not synonymous. While hydrophobic substances are usually lipophilic, there are exceptions — the silicones, for instance.
thermodynamics, matter seeks to be in a low-energy state, and bonding reduces chemical energy. Water is electrically polarized, and is able to form hydrogen bonds internally, which gives it many of its unique physical properties. But, since hydrophobes are not electrically polarized, and because they are unable to form hydrogen bonds, water repels hydrophobes, in favour of bonding with itself. It is this effect that causes the hydrophobic interaction — which in itself is incorrectly named as the energetic force comes from the hydrophilicmolecules. [Goss, K. U. and R. P. Schwarzenbach (2003): "Rules of Thumb for Assessing Equilibrium Partitioning of Organic Compounds: Successes and Pitfalls." JOURNAL OF CHEMICAL EDUCATION 80(4): 450-455. [http://jchemed.chem.wisc.edu/Journal/Issues/2003/Apr/abs450.html Link to abstract] ] Thus the two immiscible phases (hydrophilic vs. hydrophobic) will change so that their corresponding interfacial area will be minimal. This effect can be visualized in the phenomenon called phase separation.
Superhydrophobic materials have surfaces that are extremely difficult to wet, with water
contact angles in excess of 150°. Many of these very hydrophobic materials found in nature rely on Cassie's lawand are biphasicon the submicrometer level with one component air. The Lotus effectis based on this principle. An example of a biomimetic superhydrophobic material in nanotechnologyis nanopin film. In one study ["UV-Driven Reversible Switching of a Roselike Vanadium Oxide Film between Superhydrophobicity and Superhydrophilicity"Ho Sun Lim, Donghoon Kwak, Dong Yun Lee, Seung Goo Lee, and Kilwon Cho J. Am. Chem. Soc.; 2007; 129(14) pp 4128 - 4129; (Communication) DOI|10.1021/ja0692579] a vanadium pentoxidesurface is presented that can switch reversibly between superhydrophobicity and superhydrophilicityunder the influence of UV radiation. According to the study any surface can be modified to this effect by application of a suspension of rose-like V2O5 particles for instance with an inkjet printer. Once again hydrophobicity is induced by interlaminar air pockets (separated by 2.1 nm distances). The UV effect is also explained. UV light creates electron-hole pairs, with the holes reacting with lattice oxygen creating surface oxygen vacancies while the electrons reduce V5+ to V3+. The oxygen vacancies are met by water and this water absorbency by the vanadium surface makes it hydrophilic. By extended storage in the dark, water is replaced by oxygen and hydrophilicityis once again lost.
* [http://www.bmm.icnet.uk/~offman01/hydro.html Webtool to calculate and plot the hydrophobicity of proteins.]
* [http://wetenschap.infonu.nl/scheikunde/18559-hydrofobe-interactie-chromatografie.html Hydrophobicity applied - hydrophobic interaction chromatography (dutch)]
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hydrophobe — [ idrɔfɔb ] adj. et n. • 1640; lat. d o. gr. hydrophobus 1 ♦ Méd. Qui a une peur morbide de l eau. 2 ♦ Que l eau ne mouille pas. Fibre hydrophobe. ⊗ CONTR. Hydrophile. ● hydrophobe adjectif (latin hydrophobus, du grec hudrophobos) Qui évite l eau … Encyclopédie Universelle
Hydrophobe — Un composé est dit hydrophobe (du grec υδρο, hydro = eau, et Φόϐος, phóbos = peur) quand il repousse l eau ou est repoussé par l eau ; Goutte d eau sur la surface naturellement hydrophobe d une cuticule végétale … Wikipédia en Français
HYDROPHOBE — s. et adj. des deux genres T. de Médec. Celui ou celle qui a l eau et tous les liquides en horreur. On le dit particulièrement de Ceux qui sont attaqués de la rage. Il est hydrophobe. Un hydrophobe … Dictionnaire de l'Academie Francaise, 7eme edition (1835)
HYDROPHOBE — adj. des deux genres T. de Médecine Qui est atteint d’hydrophobie. Substantivement, Un hydrophobe … Dictionnaire de l'Academie Francaise, 8eme edition (1935)
hydrophobe — hy·dro·phobe hī drə .fōb n a hydrophobic substance hydrophobe adj … Medical dictionary
hydrophobe — (i dro fo b ) s. m. et f. Terme de médecine. Celui, celle qui a les liquides en horreur ; et, par extension, comme l horreur des liquides est un symptôme de la rage, enragé. Adjectivement. Un malade hydrophobe. ÉTYMOLOGIE Terme grec dérivé… … Dictionnaire de la Langue Française d'Émile Littré
hydrophobe — /huy dreuh fohb /, n. Chem. a hydrophobic substance. [1920 25; HYDRO 1 + PHOBE] * * * … Universalium
hydrophobe — noun A hydrophobic compound or material … Wiktionary
hydrophobe — hy·dro·phobe … English syllables
hydrophobe — ˈhīdrəˌfōb noun ( s) Etymology: Late Latin hydrophobus one that has hydrophobia, from hydrophobus, adjective having hydrophobia, from Greek hydrophobos, from hydr + phobos phobous : one that is averse to or sheds water … Useful english dictionary