Hamaker Constant
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Hamaker Constant

The Hamaker constant A can be defined for a van der Waals (vdW) body-body interaction:

${\displaystyle A=\pi ^{2}C\rho _{1}\rho _{2},}$

where ${\displaystyle \rho _{1}}$ and ${\displaystyle \rho _{2}}$ are the number densities of the two interacting kinds of particles, and C is the London coefficient in the particle-particle pair interaction.[1][2] 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.[1]

The Hamaker constant provides the means to determine the interaction parameter C from the vdW-pair potential, ${\displaystyle w(r)=-C/r^{6}}$.

Hamaker's method and the associated Hamaker constant ignores the influence of an intervening medium between the two particles of interaction. In the 1950s 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 ${\displaystyle 1/r^{6}}$; this is called the retarded regime, and the result is a Casimir-Polder force.