Hamaker constant

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

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

where $\rho_1$ and $\rho_2$ are the number of atoms per unit volume in two interacting bodies and C is the coefficient in the particle-particle pair interaction.^[1]

The Hamaker constant provides the means to determine the interaction parameter C from the Van der Waals pair potential, $w(r)=-C/r^6$ .

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 $1/r^6$ ; this is called the retarded regime and the result is a Casimir–Polder force.

References

↑ Seung-woo Lee and Wolfgang M. Sigmund."AFM study of repulsive Van der Waals forces between Teflon AF thin film and silica or alumina." Colloids and Surfaces A: Physicochemical and Engineering Aspects. Volume 204, Issues 1-3, 23 May 2002, Pages 43–50

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Hamaker constant

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References