Hamaker constant
The Hamaker constant A can be defined for a Van der Waals body–body interaction:
where and are the number densities of the two interacting kinds of particles, and C is the coefficient in the particle–particle pair interaction. It is named after H. C. Hamaker. 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 C from the Van der Waals pair potential,.
Hamaker's method and the associated Hamaker constant ignores the influence of an intervening medium between the two particles of interaction. In the 1950s Lifshitz developed a description of the VdW energy but with consideration of the dielectric properties of this intervening medium.
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 ; this is called the retarded regime, and the result is a Casimir–Polder force.
