Influence of Hydrolyzed Metal Ions and Surfactants on the Phase Transfer of Al2O3, SiO2, and SnO2

There are various possibilities for changing the surface properties of particles. In this work, the charge reversal on different metal oxides with different electrolytes is investigated and whether this allows a change in wettability due to a subsequent adsorption of surfactants, e.g., sodium dodecyl sulfate (SDS). It is investigated if the materials of the particles differ only by the isoelectric point or if the surface chemistry of the materials has an influence on the charge reversal as well. Furthermore, the adsorption of SDS as an anionic surfactant is examined, which is also characterized by a second charge reversal and related to a sign change of the electrophoretic mobility μe. Finally, it is examined whether the adsorption of the hydrolyzed metal ions and the subsequent adsorption of SDS are effective enough to hydrophobize the particles and allow phase transfer from the aqueous to second nonaqueous liquid phase. In addition, the influence of pH is investigated because the hydrolyzed metal cations are formed only in a certain pH range, which means that the bridge formed between the particle surface and the surfactant works only in a certain pH range, which would allow pH-selective extraction of the particle system into the second nonaqueous liquid phase.