  Interactions between silica surfaces across isopropanol solutions are
measured with colloidal probe technique based on atomic force microscope. In
particular, the influence of 1:1 electrolytes on the interactions between
silica particles is investigated. A plethora of different forces are found in
these systems. Namely, van der Waals, double-layer, attractive non-DLVO,
repulsive solvation, and damped oscillatory interactions are observed. The
measured decay length of the double-layer repulsion is substantially larger
than Debye lengths calculated from nominal salt concentrations. These
deviations are caused by pronounced ion pairing in alcohol solutions. At
separation below 10 nm, additional attractive and repulsive non-DLVO forces are
observed. The former are possibly caused by charge heterogeneities induced by
strong ion adsorption, whereas the latter originate from structuring of
isopropanol molecules close to the surface. Finally, at increased
concentrations the transition from monotonic to damped oscillatory interactions
is uncovered.
