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Abstract
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In recent years extensive experimental data on the interactions between colloids across
aqueous solutions was collected. On the other hand, the information about particle interactions
in non-aqueous solutions is still relatively scarce. For example, only a handful of studies
measuring forces in alcohols exist, although such interactions are important in practical
applications of colloids. Furthermore, comparing interactions in non-aqueous media with
the interactions across water is important also from fundamental point of view. Here we
present direct force measurements between silica particles in alcohol solutions. We study the
influence of concentration of salt and type of ion on the force between the particles. We extend
the force measurements with electrokinetic and colloidal stability experiments, which give us
additional insight into the alcohol systems. In pure alcohol the interactions between silica
surfaces is repulsive due to overlap of the double-layers. At high salt concentrations the
interactions are attractive and the van der Waals force is dominant. Interestingly, the range of
double-layer interactions in alcohols is longer as one would expect from the Debye lengths
calculated from the nominal salt concentrations. This mismatch is due to pronounced ion-paring
in alcohol solutions. In the presence of multivalent ions the charge neutralization and charge
reversal of silica are observed. Charge reversal in alcohols is much stronger and shifted to
lower concentrations as compared to the aqueous systems.
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