Interactions in Water Across Interfaces: From Nano to Macro-Scale Perspective
In this work we first revisit the surface forces between two (model) mineral surfaces, mica, across an aqueous solution (KNO3) over a broad range of concentrations. The significantly improved resolution available from the extended surface force apparatus (eSFA) allows the distinction of hydrated-ion structures. Above concentrations of 0.3 mM, hydrated-ion correlations give rise to multiple collective transitions (4 ± 1 Å) in the electrical double layers upon interpenetration. These features are interpreted as the result of hydrated-ion ordering (layering), and are responsible for hydration forces, in contrast to the traditional interpretation invoking water layering. At concentrations as low as 20 mM, attractive surface forces are measured in deviation to the DLVO theory. The estimated hydration number of the ions in the confined electrolyte is significantly below that of the bulk. A confined 1–3 nm thick ionic layer condensates at concentrations >100 mM, i.e. below bulk saturation. This study leads to new insights into crystal growth in nano-confinement that differs from the classical theory of crystallization. Finally, the impact of the properties of confined water or solution and in-pore crystallization on the macro-scale description of soil water distribution is discussed.
KeywordsSurface Force Mica Surface Hamaker Constant Surface Separation Stern Layer
I would like to acknowledge M. Heuberger, N.D. Spencer, J.F. van der Veen, and S. Chodankar for scientific discussions. Technical support for the eSFA was provided by J. Vanicek, M. Elsener and G. Cossu. This work was supported by the Swiss National Science Foundation. Selected figures from  reproduced by permission of the PCCP Owner Societies.
- 10.Derjaguin BV, Landau L (1941) Theory of the stability of strongly charged lyophobic sols and of the adhesion of strongly charged particles in solution of electrolytes. Acta Physicochim URSS 14:633–662Google Scholar
- 13.Espinosa-Marzal RM, Scherer GW (2009) Crystallization pressure exerted by in-pore confined crystals. In: Poro-mechanics IV: proceedings of the fourth biot conference on promechanics, New York, pp 1013–1018Google Scholar
- 24.Israelachvili JN (1991) Intermolecular and surface forces, 2nd edn. Elsevier, New YorkGoogle Scholar
- 38.Pashley RM (1981) DLVO and hydration forces between mica surfaces in Li+, Na+, K+, and Cs + electrolyte solutions: a correlation of double-layer and hydration forces with surface cation exchange properties. J Colloid Interface Sci 83(2):531–546. doi: 10.1016/0021-9797(81)90348-9 CrossRefGoogle Scholar
- 49.Verwey EJ, Overbeek JTG (1948) Theory of the stability of lyophobic colloids. Dover Publications, AmsterdamGoogle Scholar