(232h) Understanding Optimal Oil-in-Water Emulsifer Formulation Using Interfacial Tensiometry and Microstructural Studies

McCormick, A. - Presenter, University of Minnesota, Twin Cities
Riehm, D., University of Minnesota
Marine oil dispersants are concentrated, low-viscosity, low-toxicity surfactant-solvent blends which are applied to crude oil spills in order to disperse them into the ocean. Despite their widespread use, the fundamental principles underlying oil dispersantsâ?? formulation have remained poorly understood for decades. In our work, the dispersion effectiveness of various blends of Tween 80, Span 80, and DOSS (dioctyl sodium sulfosuccinate), three of the most widely used surfactants in marine oil dispersants, has been correlated with the dynamic crude oil-seawater interfacial tension produced by each blend. DOSS-rich blends which produce very low interfacial tensions (<10-4 mN/m) exhibit high dispersion effectiveness; DOSS-poor blends producing comparably low interfacial tensions exhibit much lower effectiveness, because DOSS-poor dispersantsâ?? initial adsorption to the oil-water interface is much slower than that of DOSS-rich dispersants. Cryo-transmission electron microscopy (cryo-TEM) and dynamic light scattering (DLS) show that these solutions contain spherical W/O microstructures, the size and dispersity of which vary with surfactant blend composition and surfactant:seawater molar ratio. Span 80-rich microstructures exhibit high polydispersity index (PDI > 0.2) and large diameters (â?¥100 nm), whereas DOSS-rich microstructures exhibit smaller diameters (20-40 nm) and low polydispersity index (PDI < 0.1), indicating a narrow microstructure size distribution. The smaller diameters of DOSS-rich microstructures, as well as the fact that DOSS molecules, being oil-soluble, can diffuse to a bulk oil-water interface as monomers much faster than any of these microstructures, may explain why DOSS-rich blends adsorb to the oil-water interface more quickly than Span 80-rich blends, a phenomenon which has been linked in prior work to the higher effectiveness of DOSS-rich Tween/Span/DOSS-based oil dispersants.