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Sign of the Casimir-Polder interaction between atoms and oil-water interfaces: Subtle dependence on dielectric properties

Mathias Boström, Simen Å. Ellingsen, Iver Brevik, Drew F. Parsons, and Bo E. Sernelius


Phys. Rev. A, 85, 064501 (2012)


We demonstrate that Casimir-Polder energies between noble gas atoms (dissolved in water) and oil-water interfaces are highly surface specific. Both repulsion (e.g.   hexane) and attraction (e.g. glycerine and cyclodecane) is found with different oils. For several intermediate oils (e.g. hexadecane, decane, and cyclohexane) both attraction and repulsion can be found in the same system. Near these oil-water interfaces the interaction is repulsive in the non-retarded limit and turns attractive at larger distances as retardation becomes important. These highly surface specific interactions may have a role to play in biological systems where the surface may be more or less accessible to dissolved atoms.

The usefulness to industrial applications of the results exemplified herein would appear to be immediate. One can envisage separation of different species of particles dissolved in water, for example, by carefully choosing an interface by which one species is attracted, the other repelled, allowing selective adsorption .

Fig. Geometry considered: an atom immersed in water near an interface with an oil.

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Last updated: 06/22/12