Electrostatic depletion forces between planar surfaces

Marius M. Hatlo, R.A. Curtis, Leo Lue

Research output: Contribution to journalArticle

30 Citations (Scopus)

Abstract

The interaction between two dielectric plates immersed in an electrolyte solution is examined by using a variational perturbation approximation for the grand partition function. This approach differs from previous treatments in that the screening length between the plates is treated as a variational parameter. A key finding is that adjacent to each plate is a layer of ion depletion with thickness given by about one-half of a Bjerrum length. Consequently, for plate-plate separations less than the Bjerrum length, nearly all the electrolyte is excluded from between the plates, and the interaction is given by the sum of a van der Waals interaction and an attractive osmotic depletion force. In contrast to the predictions of previous theories, the interaction between the plates at short range increases with increasing electrolyte concentration and may provide an important contribution to the salt-induced attraction, commonly referred to as salting out. Because the range of the osmotic depletion force is roughly equal to the Bjerrum length, it increases with the square of the valency of the electrolyte. At larger plate-plate separations, the van der Waals interaction is screened as electrolyte enters the space between the plates, leading to an exponential decay of the interactions, as has been previously observed. However, this interaction is slightly stronger than that previously predicted, due to ion depletion from the surface of the interface, also this effect increases with increasing electrolyte concentration.
LanguageEnglish
Article number164717
Number of pages11
JournalJournal of Chemical Physics
Volume128
Issue number16
DOIs
Publication statusPublished - 28 Apr 2008

Fingerprint

Electrostatic force
Electrolytes
depletion
electrostatics
electrolytes
interactions
Ions
Screening
Salts
attraction
partitions
ions
screening
salts
perturbation

Keywords

  • dielectric materials
  • electrolytes
  • electrostatics
  • osmosis
  • permittivity
  • perturbation theory
  • plates (structures)
  • variational techniques

Cite this

Hatlo, Marius M. ; Curtis, R.A. ; Lue, Leo. / Electrostatic depletion forces between planar surfaces. In: Journal of Chemical Physics. 2008 ; Vol. 128, No. 16.
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Electrostatic depletion forces between planar surfaces. / Hatlo, Marius M.; Curtis, R.A.; Lue, Leo.

In: Journal of Chemical Physics, Vol. 128, No. 16, 164717 , 28.04.2008.

Research output: Contribution to journalArticle

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