Hydrophobe


Hydrophobe

In 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-polar and 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 molecules include 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.

Chemical background

According to 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 hydrophilic molecules. [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.

Superhydrophobicity

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 law and are biphasic on the submicrometer level with one component air. The Lotus effect is based on this principle. An example of a biomimetic superhydrophobic material in nanotechnology is 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 pentoxide surface is presented that can switch reversibly between superhydrophobicity and superhydrophilicity under 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 hydrophilicity is once again lost.

References

External links

* [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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Look at other dictionaries:

  • 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


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