Hamaker constant

In molecular physics, the Hamaker constant (denoted Template:Mvar; named for H. C. Hamaker) is a physical constant that can be defined for a van der Waals (vdW) body–body interaction:

$A={\pi }^{2}C{\rho }_1{\rho }_2,$

where ρ₁, ρ₂ are the number densities of the two interacting kinds of particles, and Template:Mvar 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.

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

$w(r)=\frac{-C}{r^6}.$

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 are effective only up to several hundred angstroms. 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.

See also

• Hamaker theory
• Intermolecular forces
• van der Waals Forces

References

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