Interactions in Water Across Interfaces: From Nano to Macro-Scale Perspective

摘要

In this work we first revisit the surface forces between two (model) mineral surfaces, mica, across an aqueous solution (KNO_3) 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 A) 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.