مجتبی فرخ بین

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.