  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.
