Fortenberry, A. W.; Reed, D. M.; Smith, A. E.; Scovazzo, P. “Quantifying the Stability of Magnetic Surfactants in Aqueous Solution.” 2018 AIChE Annual Meeting, Pittsburgh, PA, United States, October 28 – November 2, 2018.
Predicting the behavior of magnetic surfactants at air/water and oil/ water interfaces in different environments is critical for their application to certain processes such as oil/ water separations and the tuning of surface tensions. The ability of magnetic surfactants to alter interfacial properties is dependent upon the strength of association between the magnetic and surfactant moieties of the surfactant molecules. This research shows that the strength of association of a magnetic surfactant in an aqueous environment is dependent upon the type of complex that contains the ferromagnetic ion. These findings provide valuable insight into the design of magnetic surfactants for applications in aqueous media. The surfactants investigated were either cationic surfactants that possessed magnetic-metal halide counterions (Type 1 surfactants), or they were surfactants that possessed headgroups that chelated directly with a magnetic-metal ion (Type 2 surfactants). By utilizing electrochemical methods like solution conductivity, cyclic voltammetry (CV), and sampled current voltammetry (SCV); we determined the strengths of association between the magnetic and surfactant components as functions of various aqueous solution properties; such as, pH, ionic strength, temperature, etc. Based on these results, we developed a model to predict the behavior of some Type 1 and Type 2 surfactants in different aqueous environments. This model helps to determine which conditions will favor the strong association between the magnetic and surfactant moieties.
Reed, D. M.; Koehler, E. A.; Stanhope, R. A.; Fortenberry, A. W.; Smith, A. E.; Scovazzo, P. “Magnetic Surfactant Surface Tension Functionality Vs. Magnetic Field Gradients.” 2018 AIChE Annual Meeting, Pittsburgh, PA, United States, October 28 – November 2, 2018.
Literature reports that magnetic surfactants with magnetic-metal halides undergo a reduction in surface tension when exposed to magnetic fields with field strength gradients. We tested the hypothesis that the magnitude of the reported responses are dominated by an artificial magnetic gravity effect instead of a change in surface energy of the aqueous system. To test our hypothesis, we studied the behavior of magnetically responsive surfactants at the air-water interface using a shape-dependent pendant drop method in parallel magnetic fields. This research showed that the magnitude of the magnetic surfactant’s response to external magnetic fields depends upon the gradients in the field strength. By utilizing a parallel magnetic field with negligible field strength gradients, the effects of artificial gravity on drop shape are mitigated, so the change in surface tension is a result of the magnetic field alone. To gain insights into surfactant behavior on the molecular level we quantified the response of the magnetic surfactants both experimentally and using Ferrohydrodynamic energy models. We plan on using these insights in the design of magnetic driven separation processes.
Smith, A. E.; Scovazzo, P. “Magnetic Responsive Polymeric Colloids for Advanced Separations.” 2015 AIChE Annual Meeting, Salt Lake City, UT, United States, November 8 – 13, 2015.
Surfactants are widely used in industrial separation processes ranging from ore purification to environmental remediation. Separation systems involving surfactants could be made more efficient and / or cost effective with magnetic surfactants. Zubarev’s theory states that a magnetic field can cause significant changes in the size and shape of magnetic polymer coils. In order to test this theory, we synthesized novel magneto-responsive polymer-based surfactants by first synthesizing and adding magnetic functionality to pH-responsive polymeric colloids. We utilized reversible addition-fragmentation chain transfer (RAFT) polymerization to synthesize a family of pH-responsive cationic ammonium homo- and block copolymers. RAFT provides a facile method for synthesizing advanced polymer architectures from a variety of functional monomers while maintaining precise control over the macromolecular design (molecular weight, copolymer composition, functionality). We examined the pH-response of a poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) (pKa ~ 7.3) series using dynamic light scattering to determine the hydrodynamic diameter of the polymers in solution at two pH values. At a solution pH of 4.0, the tertiary amine moieties along the polymer backbone were ionized enough for the polymers to be molecularly dissolved. At a pH of 10.4, however, the tertiary amine functionality is essentially 100% deprotonated. The corresponding decrease in hydrophilicity induced self-assembly into micelles with a diameter of roughly 60 nm. The pH-responsive, cationic polymers were rendered magneto-responsive via an ion exchange paramagnetic ions such as FeCl4– or CoCl42-. Ongoing efforts focus on the effect of magnetic fields on the solubilization capacity of the polymeric micelles and the ability of utilizing the magneto-responsive polymeric micelles to affect low energy extraction and concentration of organics solutes.