Wetting and drying scenarios of ionic solutions.

Anna Oleksy (1) , Jean-Pierre Hansen (2)

1 CAM - University of Cambridge [UK]
2 Chemistry

We review recent theoretical results obtained for the wetting and drying behaviour of ionic solutions near a charged solid substrate. Three levels of modelling ionic solutions are considered: the primitive model, where the solvent is replaced by a dielectric continuum; the "semi-primitive" model where the solvent is represented by hard spheres with a Yukawa attraction and a dielectric permittivity is introduced, which depends on the local solvent density; and the "civilized" model, where the solvent molecules are dipolar hard spheres with a Yukawa attraction. Qualitative agreement is found between the predictions of the three models, while those of the two discrete solvent models agree quantitavely. The relative size of anions and cations is shown to have a crucial influence on interfacial properties, as observed experimentally. A novel drying scenario is predicted near a charged wall. New results are reported for the variation of the surface tension γ with ion concentration c. Contrary to the observed behaviour of aqueous ionic solutions, the liquid/vapour surface tension is found to systematically decrease with c, presumably because our solvent models are insufficient to describe water, due to the neglect of strong hydrogen bonding. The solid/liquid surface tension is in contrast shown to be a non-monotonic function of c which has a minimum.

Mots clés: Physical Sciences

Domaines: Matière Condensée [cond-mat]

Anna Oleksy, Jean-Pierre Hansen. Wetting and drying scenarios of ionic solutions.. Molecular Physics, 2011, 109 (07-10), pp.1275-1288. ⟨10.1080/00268976.2011.554903⟩. ⟨hal-00692117⟩