Van der Waals force

The van der Waals force (or van der Waals interaction), named after Dutch scientist Johannes Diderik van der Waals, is the attractive or repulsive force between molecules (or between parts of the same molecule) other than those due to covalent bonds or to the electrostatic interaction of ions with one another or with neutral molecules. It is also sometimes used loosely as a synonym for the totality of intermolecular forces. Van der Waals forces are relatively weak compared to normal chemical bonds, but play a fundamental role in fields as diverse as supramolecular chemistry, structural biology, polymer science, nanotechnology, surface science, and condensed matter physics. Van der Waals forces define the chemical character of many organic compounds. They also define the solubility of organic substances in polar and non-polar media. In low molecular weight alcohols, the properties of the polar hydroxyl group dominate the weak intermolecular forces of van der Waals. In higher molecular weight alcohols, the properties of the nonpolar hydrocarbon chain(s) dominate and define the solubility. Van der Waals forces grow with the length of the nonpolar part of the substance.Contents Van der Waals forces include attractions between atoms, molecules, and surfaces. They differ from covalent and ionic bonding in that they are caused by correlations in the fluctuating polarizations of nearby particles (a consequence of quantum dynamics). Intermolecular forces have four major contributions. In general an intermolecular potential has a repulsive component (which prevents the collapse of molecules because as entities move closer to one another these repulsions dominate).  All intermolecular/van der Waals forces are anisotropic (except those between two noble gas atoms), which means that they depend on the relative orientation of the molecules. The induction and dispersion interactions are always attractive, irrespective of orientation, but the electrostatic interaction changes sign upon rotation of the molecules. That is, the electrostatic force can be attractive or repulsive, depending on the mutual orientation of the molecules. When molecules are in thermal motion, as they are in the gas and liquid phase, the electrostatic force is averaged out to a large extent, because the molecules thermally rotate and thus probe both repulsive and attractive parts of the electrostatic force. Sometimes this effect is expressed by the statement that "random thermal motion around room temperature can usually overcome or disrupt them" (which refers to the electrostatic component of the van der Waals force). Clearly, the thermal averaging effect is much less pronounced for the attractive induction and dispersion forces. Van der Waals forces are responsible for certain cases of pressure broadening (van der Waals broadening) of spectral lines and the formation of van der Waals molecules.

Further information

1. Стид Дж.В., Этвуд Дж.Л. Супрамолекулярная химия. - Т.1.В 2 т. - М.: Академкнига, 2007 - глава 1.7.7.
2. Dai L.Intelligent Macromolecules for Smart Devices: from Materials Synthesis to Device Applications.-London:Springer-Verlag,2004
3. Iver Brevik, V. N. Marachevsky, Kimball A. Milton, Identity of the Van der Waals Force and the Casimir Effect and the Irrelevance of these Phenomena to Sonoluminescence, hep-th/9901011
4. I. D. Dzyaloshinskii, E. M. Lifshitz, and L. P. Pitaevskii, Usp. Fiz. Nauk 73, 381 (1961)
5. English translation: Soviet Phys. Usp. 4, 153 (1961)
6. L. D. Landau and E. M. Lifshitz, Electrodynamics of Continuous Media, Pergamon, Oxford, 1960, pp. 368–376.
7. Mark Lefers, "Van der Waals dispersion force". Holmgren Lab.
8. E. M. Lifshitz, Zh. Eksp. Teor. Fiz. 29, 894 (1955)
9. English translation: Soviet Phys. JETP 2, 73 (1956)
10. Western Oregon University's "London force". Intermolecular Forces. (animation)
11. J. Lyklema, Fundamentals of Interface and Colloid Science, page 4.43
12. Article Van der Waals force from Wikipedia, the Free Enciclopedia. Available under the license Creative Commons Attribution-Share Alike.

Back to Russian