Partition of hematite in the Triton X-100/Dextran aqueous biphase system

The principle behind the partition of inorganic particles in aqueous biphase systems is the physicochemical interaction between the solid surface and the surrounding liquid solution. This study demonstrates that many factors, such as hydrophilic/hydrophobic properties, polymer–solid specific interaction, and electrostatic effects, may influence the partition of metal oxides in aqueous biphase systems. In the Triton X-100/dextran/water system, hematite stays in the bottom dextran-rich phase under all pH conditions. This behavior is attributable to the hydrophilic nature of the solid surface and the strong interaction between dextran and ferric oxide. Anionic surfactants, e.g., sodium dodecylsulfate (SDS) or sodium oleate, have no effect on the solids partition; on the other hand, the cationic surfactant dodecyltrimethylammonium bromide (DTAB) is able to transfer the particles from the bottom to the top phase at high pH. Based on adsorption experiments, it is proposed that electrostatic interactions between the mixed micelles in the top phase and the particle surface play a dominant role in controlling the solids distribution.