Stability of Ionic Magnetic Surfactants in Aqueous Solutions: Measurement Techniques and Impact on Magnetic Processes

Predicting the behavior of magnetic surfactants in magnetic fields is critical for designing magnetically driven processes such as chemical separations or the tuning of surface tensions. The ability of magnetic fields to alter the interfacial properties of magnetic surfactant solutions may be dependent upon the strength of association between the magnetic and surfactant moieties of the surfactant molecules. This research shows that the stability of a magnetic surfactant in an aqueous environment is dependent upon the type of complex that contains the paramagnetic ion, and these findings provide valuable insight for the design of magnetic surfactants for applications in aqueous media. The surfactants investigated were ionic surfactants, which contained paramagnetic counterions. This investigation looked at both anionic and cationic surfactants; it utilized solution conductivity, cyclic voltammetry (CV), sampled current voltammetry (SCV), and solution pH measurements to qualitatively evaluate the stability of the magnetic counterions in aqueous solution. In addition, solution conductivity was used to quantify the degree of binding between the paramagnetic ions and surfactant micelles in solution. These results indicate metal halide-based cationic surfactants are unstable in aqueous solutions. We hypothesize that this instability results in the difference in the magnetic response of the anionic vs cationic surfactants examined in this study.