Cation capture and overcharging of a hydrophobized quartz surface in concentrated potassium chloride solutions

The paper presents experimental data indicating interesting new phenomena related to overcharging of a hydrophobic surface in concentrated potassium chloride solutions. We attribute these data to cation complexation and capture of the cations by the hydrophobic surface. The analysis of the mechanism of the detected phenomena is based on capillary electrokinetic and wettability studies and confirmed by SEM data and XPS spectra. It was found that cation capture/complexation takes prolonged time, being associated with hydrolysis of Si-O bonds in hydrophobic molecules and affected by salt concentration. In addition, the time necessary for reversal of the sign of zeta-potential when solutions with lower salt concentrations are pumped through the hydrophobic capillary is much longer than that required to simply replace the solution inside the capillary.