Breakup of Oil Jets into Droplets in Seawater with Environmentally Benign Nanoparticle and Surfactant Dispersants

During deep-sea oil leaks, dispersants may be used to break up the oil into droplets smaller than about 70 μm, which may then be bioremediated by bacteria before they reach the ocean surface. To investigate the mechanism of droplet formation as a function of dispersant type, concentration, and jet velocity, a flowing oleophilic stream containing amphiphiles was mixed with flowing dodecane and then atomized through a 0.25 mm circular nozzle. The minimum droplet diameters were 2.2, 4.5, and 24 μm for only 5 w:v % amphiphile in the oil phase for Corexit 9500A, Tergitol 15-S-7 (C12H25CH­(OCH2CH2)7OH), and a silica nanoparticle/Span 20 mixture, respectively. For Tergitol 15-S-7, the droplet size exhibited the expected scaling with Weber number (We) at low viscosity numbers (Vi < 50), where inertial forces overcome interfacial forces, and Reynolds number (Re) at high Vi numbers (Vi > 50), where inertial forces overcome viscous forces. However, in the case of the silica nanoparticle/Span 20 mixture, the magnitude of the exponent of We scaling was found to be smaller than −3/5. A better understanding of how low concentrations of dispersants (with relatively high oil–water interfacial tensions) may be used to provide a sufficient We with high inertial forces (high Re) in jets to form small oil droplets, which is of interest for advancing environmental protection in the undesired event of a deep-sea oil leak.