Colloidal and Physicochemical Characterization of Highly Magnetic O/W Magnetic Emulsions

Abstract

A study of magnetic emulsion droplets is reported using various analytical and physico‐chemical techniques. The chemical composition of the droplets (i.e., the amount of iron oxide, organic phase, and surfactant) is determined using the combination of thermogravimetry, elemental analysis, and gas chromatography. The electrokinetic properties of the magnetic emulsion are investigated as a function of pH and ionic strength in order to estimate the surface potential (ψ₀) and the shear‐plane position. The droplet surface potential and charge density are deduced from electrophoretic mobility measurements. The surface potential value obtained is in good agreement with one deduced from independent force measurements performed between emulsion droplets. The emulsion stability as a function of the continuous phase ionic strength is evaluated through the experimental determination of the critical coagulation concentration (CCC). A value for the Hamaker constant (A) that quantifies the van der Waals attraction between two emulsion droplets is deduced. In addition, the colloidal force between magnetic droplets is investigated as a function of pH and salt concentration and the surface potentials obtained are compared to the measured zeta potential and deduced diffuse potentials. The results from such an analysis are consistent with those reported in the literature.

Keywords:

• Iron oxide
• Ferrofluid
• Magnetic emulsion
• Zeta potential
• Surface potential
• Colloidal stability
• Critical coagulation concentration
• Hamaker constant
• Colloidal forces

Acknowledgments

This work was supported by the bioMérieux Company. The authors acknowledge the technical assistance of Ademtech SA; Parc Scientifique Unitec 1, 4 allée du Doyen Georges Brus, 33600‐Pessac, France.