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## Surface energy
## Additional recommended knowledgeIf the cutting is done reversibly (see reversible), then conservation of energy means that the energy consumed by the cutting process will be equal to the energy inherent in the two new surfaces created. The unit surface energy of a material would therefore be half of its energy of cohesion, all other things being equal; in practice, this is true only for a surface freshly prepared in vacuum. Surfaces often change their form away from the simple "cleaved bond" model just implied above. They are found to be highly dynamic regions, which readily rearrange or react, so that energy is often reduced by such processes as passivation or adsorption. As first described by Thomas Young in 1805 in the Surface energy is most commonly quantified using a contact angle goniometer and a number of different methods. Thomas Young described surface energy as the interaction between the forces of cohesion and the forces of adhesion which, in turn, dictate if wetting occurs. If wetting occurs, the drop will spread out flat. In most cases, however, the drop will bead to some extent and by measuring the contact angle formed where the drop makes contact with the solid the surface energies of the system can be measured. Young developed the well-regarded Young's Equation which defines the balances of forces caused by a wet drop on a dry surface. If the surface is hydrophobic then the contact angle of a drop of water will be larger. Hydrophilicity is indicated by smaller contact angles and higher surface energy. (Water has rather high surface energy by nature; it is polar and forms hydrogen bonds).
The Young equation gives the following relation:
Y Where Y a Where R and
R
## See also## References**^**Rafael Tafmor. "Line energy and the relation between advancing, receding and Young contact angles", Langmuir, 20, 7659-7664, (2004).**^**Pierre-Gilles de Gennes, Françoise Brochard-Wyart, David Quéré (2002).*Capillary and Wetting Phenomena -- Drops, Bubbles, Pearls, Waves*. Springer.__ISBN 0-387-00592-7__.
Categories: Condensed matter physics | Surface chemistry |

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Surface_energy". A list of authors is available in Wikipedia. |