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In physical chemistry, the van der Waals forces (or van der Waals' interaction), named after Dutch scientist Johannes Diderik van der Waals, are the residual attractive or repulsive forces between molecules or atomic groups that do not arise from a covalent bond, or electrostatic interaction. The resulting van der Waals forces can be attractive or repulsive. The term includes: * force between two permanent dipoles (Keesom force) * force between a permanent dipole and a corresponding induced dipole (Debye force) * force between two instantaneously induced dipoles (London dispersion force). It is also sometimes used loosely as a synonym for the totality of intermolecular forces. Van der Waals forces are relatively weak compared to covalent 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 many properties of organic compounds, including their solubility in polar and non-polar media. In low molecular weight alcohols, the hydrogen-bonding properties of the polar hydroxyl group dominate other weaker van der Waals interactions. In higher molecular weight alcohols, the properties of the nonpolar hydrocarbon chain(s) dominate and define the solubility. Van der Waals forces quickly vanish at longer distances between interacting molecules. In 2012, the first direct measurements of the strength of the van der Waals force for a single organic molecule bound to a metal surface was made via atomic force microscopy and corroborated with density functional calculations.〔http://www.columbia.edu/~sva2107/media/Aradhya_NMat_2012.pdf〕 ==Definition== Van der Waals forces include attractions and repulsions between atoms, molecules, and surfaces, as well as other intermolecular forces. 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〔 Chapter 6 Electromagnetic Radiation in an Absorbing Medium〕). Intermolecular forces have four major contributions: # A repulsive component resulting from the Pauli exclusion principle that prevents the collapse of molecules. # Attractive or repulsive electrostatic interactions between permanent charges (in the case of molecular ions), dipoles (in the case of molecules without inversion center), quadrupoles (all molecules with symmetry lower than cubic), and in general between permanent multipoles. The electrostatic interaction is sometimes called the Keesom interaction or Keesom force after Willem Hendrik Keesom. # Induction (also known as polarization), which is the attractive interaction between a permanent multipole on one molecule with an induced multipole on another. This interaction is sometimes called Debye force after Peter J.W. Debye. # Dispersion (usually named after Fritz London), which is the attractive interaction between any pair of molecules, including non-polar atoms, arising from the interactions of instantaneous multipoles. Returning to nomenclature, different texts refer to different things using the term "van der Waals force." Some texts describe the van der Waals force as the totality of forces (including repulsion); others mean all the attractive forces (and then sometimes distinguish van der Waals-Keesom, van der Waals-Debye, and van der Waals-London). 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. The Lennard-Jones potential is often used as an approximate model for the isotropic part of a total (repulsion plus attraction) van der Waals force as a function of distance. 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. The London-van der Waals forces are related to the Casimir effect for dielectric media, the former being the microscopic description of the latter bulk property. The first detailed calculations of this were done in 1955 by E. M. Lifshitz.〔For further investigation, one may consult the University of St. Andrews' levitation work in a popular article: (Science Journal: ''New way to levitate objects discovered'' ), and in a more scholarly version: (New Journal of Physics: ''Quantum levitation by left-handed metamaterials'' ), which relate the Casimir effect to the gecko and how the reversal of the Casimir effect can result in physical levitation of tiny objects.〕 A more general theory of van der Waals forces has also been developed. The main characteristics of van der Waals forces are:- 〔''Chemical Bonding'' - Ms Shethi and M. Satake〕 * They are weaker than normal covalent ionic bonds. * Van der Waals forces are additive and cannot be saturated. * They have no directional characteristic. * They are all short-range forces and hence only interactions between nearest need to be considered instead of all the particles. The greater is the attraction if the molecules are closer due to Van der Waals forces. * Van der Waals forces are independent of temperature except dipole - dipole interactions. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Van der Waals force」の詳細全文を読む スポンサード リンク
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