Journal article
Approaches to hydration, old and new: Insights through Hofmeister effects
Current Opinion in Colloid & Interface Science, Vol.16(6), pp.612-617
2011
Abstract
Hydration effects in colloidal interactions or problems involving electrolytes are usually taken care of by effective electrostatic potentials that subsume notions like hydrated ion size, Gurney potentials, soft and hard, chaotropic and cosmotropic ions, and inner and outer Helmholtz planes. Quantum fluctuation (dispersion) forces between ions and between ions and surfaces are missing from classical theories, at least not explicit in standard approaches to hydration. This paper outlines an evolving back-to-basics approach that allows these ion specific forces to be included in theories quantitatively. In this approach ab initio quantum mechanics is used to calculate dynamic polarisabilities of ions and to quantify bare ion radii. The ionic dispersion potentials between ions, and between ions and surfaces in water can then be given explicit analytic form from an extension of Lifshitz theory. They are included in the theory along with electrostatic potentials. In a first stage the primitive (continuum solvent) model provides a skeletal theory on which to build in hydration. Extension of the ab initio calculations to include "dressed" ions, i.e. water hydration shells for cosmotropic ions, quadrupolar and octupolar polarisability contributions and; for colloids, allowance for a surface hydration layer, permits quantification of Hofmeister effects and Gurney potentials. With these extensions, primary hydration forces (short range repulsion) arise due to an interplay between surface hydration layers and specific ion interactions. Apparent longer range "secondary hydration forces" are shown to be a consequence of ion-surface dispersion interactions and are not true "hydration forces".
Details
- Title
- Approaches to hydration, old and new: Insights through Hofmeister effects
- Authors/Creators
- B.W. Ninham (Author/Creator) - Australian National UniversityT.T. Duignan (Author/Creator) - Australian National UniversityD.F. Parsons (Author/Creator) - Australian National University
- Publication Details
- Current Opinion in Colloid & Interface Science, Vol.16(6), pp.612-617
- Publisher
- Elsevier
- Identifiers
- 991005540345007891
- Copyright
- © 2011 Elsevier Ltd.
- Murdoch Affiliation
- Murdoch University
- Language
- English
- Resource Type
- Journal article
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- Citation topics
- 2 Chemistry
- 2.89 Ionic, Molecular & Complex Liquids
- 2.89.677 Liquid Water
- Web Of Science research areas
- Chemistry, Physical
- ESI research areas
- Chemistry