van der Waals interaction
otherwise
van der Waals force
(rus. взаимодействие, ван-дер-ваальсово otherwise ван-дер-ваальсовы силы)
—
weak noncovalent intermolecular interaction, arising from the interaction of the dipole (multipole) moments of the molecules and polarisation of their electron shells.
Description
The van der Waals interaction is the attractive forces at large distances between any molecules, both polar and non-polar. At very short distances the interaction is repulsive due to repulsion of electron shells. There are the following main types of van der Waals interactions:
1. Orientation (dipole-dipole) interaction between polar molecules, i.e. molecules with permanent dipole moments. The interaction potential (
) of rigidly oriented dipoles is anisotropic, i.e. it depends on the orientation of the permanent dipole. It is proportional to the squares of the dipole moments (
and 
) and is inversely proportional to the temperature (
) and the sixth power of the distance between the dipoles (
):
.
In addition, there is interaction between the dipole moments and the higher multipole moments (for example, dipole-quadrupole interaction) and interaction of the latter with each other, but the respective contributions are usually much weaker.
2. Induced dipole (permanent dipole-induced dipole) interaction between polar and non-polar molecules, where the permanent dipole moment of the first molecule (
) interacts with the moment induced by its field in the second molecule. In this case, the potential is inversely proportional to the sixth power of the distance and directly proportional to the polarisability of the non-polar molecule (
) and the square of the permanent dipole moment:
.
As in previous cases similar effects generated by the higher multipole moments may be present, but they are much less significant.
3. London dispersion (induced dipole-induced dipole) interaction, i.e. interaction of the moments that arise, in the classical model, as a result of instantaneous charge fluctuations (see details in the article on dispersion interaction). Its potential is also inversely proportional to the sixth power of the distance and increases with increasing polarisability of the particles:
.
1. Orientation (dipole-dipole) interaction between polar molecules, i.e. molecules with permanent dipole moments. The interaction potential (
) of rigidly oriented dipoles is anisotropic, i.e. it depends on the orientation of the permanent dipole. It is proportional to the squares of the dipole moments ( and ) and is inversely proportional to the temperature () and the sixth power of the distance between the dipoles (): . In addition, there is interaction between the dipole moments and the higher multipole moments (for example, dipole-quadrupole interaction) and interaction of the latter with each other, but the respective contributions are usually much weaker.
2. Induced dipole (permanent dipole-induced dipole) interaction between polar and non-polar molecules, where the permanent dipole moment of the first molecule (
) interacts with the moment induced by its field in the second molecule. In this case, the potential is inversely proportional to the sixth power of the distance and directly proportional to the polarisability of the non-polar molecule () and the square of the permanent dipole moment: . As in previous cases similar effects generated by the higher multipole moments may be present, but they are much less significant.
3. London dispersion (induced dipole-induced dipole) interaction, i.e. interaction of the moments that arise, in the classical model, as a result of instantaneous charge fluctuations (see details in the article on dispersion interaction). Its potential is also inversely proportional to the sixth power of the distance and increases with increasing polarisability of the particles:
. Among those mentioned above, dispersion interactions are usually the strongest. For small molecules the energy of van der Waals interactions can be close to 1-30 kJ/mol. Van der Waals interactions occurs not only between molecules but also between nano-objects such as carbon nanotubes.
Despite the weakness of such interaction, it ensures the stability of molecular crystals, clathrates and supramolecular complexes, as well as molecule-surface bonds (adsorption), and plays an important role in the processes of synthesis and self-assembly of molecular nanostructures.
Despite the weakness of such interaction, it ensures the stability of molecular crystals, clathrates and supramolecular complexes, as well as molecule-surface bonds (adsorption), and plays an important role in the processes of synthesis and self-assembly of molecular nanostructures.
Illustrations
|
Examples of van der Waals interactions.
|
Author
- Eremin Vadim V.
Sources
- Steed JW., Atwood JL Supramolecular Chemistry — Chichester: John Wiley & Sons Ltd, 2000.
- Dai L. Intelligent Macromolecules for Smart Devices: from Materials Synthesis to Device Applications. — London: Springer-Verlag, 2004. — 496 p.