molecular physics Molecular physics is the study of the physical properties of molecules and molecular dynamics. The field overlaps significantly with physical chemistry, chemical physics, and quantum chemistry. It is often considered as a sub-field of atomic, mo ...

, the Hamaker constant (denoted ; named for H. C. Hamaker) is a

physical constant A physical constant, sometimes fundamental physical constant or universal constant, is a physical quantity that cannot be explained by a theory and therefore must be measured experimentally. It is distinct from a mathematical constant, which has a ...

that can be defined for a van der Waals (vdW) body–body interaction: :

A=\pi^2C\rho_1\rho_2,

where are the number densities of the two interacting kinds of particles, and is the London coefficient in the particle–particle pair interaction. The magnitude of this constant reflects the strength of the vdW-force between two particles, or between a particle and a

substrate Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached ** Substrate (aquatic environment), the earthy material that exi ...

. The Hamaker constant provides the means to determine the interaction parameter from the vdW-pair potential, :

w(r) = \frac.

Hamaker's method and the associated Hamaker constant ignores the influence of an intervening medium between the two particles of interaction. In 1956 Lifshitz developed a description of the vdW energy but with consideration of the dielectric properties of this intervening medium (often a continuous phase). The

Van der Waals forces In molecular physics and chemistry, the van der Waals force (sometimes van der Waals' force) is a distance-dependent interaction between atoms or molecules. Unlike ionic or covalent bonds, these attractions do not result from a chemical ele ...

are effective only up to several hundred

angstrom The angstrom (; ) is a unit of length equal to m; that is, one ten-billionth of a metre, a hundred-millionth of a centimetre, 0.1 nanometre, or 100 picometres. The unit is named after the Swedish physicist Anders Jonas Ångström (1814–18 ...

s. When the interactions are too far apart, the dispersion potential decays faster than

1/r^6;

this is called the retarded regime, and the result is a Casimir–Polder force.

References

Physical chemistry Intermolecular forces {{molecular-physics-stub

See also

References