Physics:Hamaker constant
In molecular physics, the Hamaker constant (denoted A; named for H. C. Hamaker) is a physical constant that can be defined for a van der Waals (vdW) body–body interaction:
- [math]\displaystyle{ A=\pi^2C\rho_1\rho_2, }[/math]
where ρ1, ρ2 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] 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,
- [math]\displaystyle{ w(r) = \frac{-C}{r^6}. }[/math]
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).[3]
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 [math]\displaystyle{ 1/r^6; }[/math] 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
- ↑ 1.0 1.1 Hamaker, H. C. (1937). "The London – van der Waals attraction between spherical particles". Physica 4 (10): 1058–1072. doi:10.1016/S0031-8914(37)80203-7. Bibcode: 1937Phy.....4.1058H.
- ↑ Seung-woo Lee and Wolfgang M. Sigmund (23 May 2002). "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 204 (1–3): 43–50. doi:10.1016/S0927-7757(01)01118-9.
- ↑ Lifshitz, E.M. (1956). "The Theory of Molecular Attractive Forces between Solids". Soviet Journal of Experimental and Theoretical Physics 2: 73–83.
 |  |
