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| Paper IPM / Physic / 12584 |
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We study the interaction between two neutral plane-parallel dielectric bodies in the presence of a
highly asymmetric ionic fluid, containing multivalent as well as monovalent (salt) ions. Image charge
interactions, due to dielectric discontinuities at the boundaries, as well as effects from ion confinement
in the slit region between the surfaces are taken fully into account, leading to image-generated
depletion attraction, ion correlation attraction, and steric-like repulsive interactions. We investigate
these effects by employing a combination of Monte Carlo simulation methods, including explicit-ion
simulations (where all electrostatic interactions are simulated explicitly) and implicit-ion simulations
(where monovalent ions are replaced by an effective screened electrostatic potential between multivalent
ions), as well as an approximate analytical theory. The latter incorporates strong ion-image
charge correlations, which develop in the presence of high valency ions in the mixture.We show that
the implicit-ion simulations and the proposed analytical theory can describe the explicit simulation
results on a qualitative level, while excellent quantitative agreement can be obtained for sufficiently
large monovalent salt concentrations. The resultant attractive interaction between the neutral surfaces
is shown to be significant, as compared with the usual van der Waals interactions between semi-infinite dielectrics, and can thus play an important role at the nano scale.
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