(750c) Oil Emulsification by Surface-Tunable Carbon Black Particles

Dispersants were used extensively to emulsify crude oil during the Deepwater Horizon oil spill.  In contrast to surfactant-stabilized emulsions, ones that are stabilized by interfacially active particles can remain stable at large background dilutions and can also be used to absorb toxic polycyclic aromatic hydrocarbons and thus lower their concentrations in the aqueous phase.  We examine particle stabilized octane-in-water emulsions prepared by modifying the pH or varying the salt concentration of an amino-benzoic acid terminated carbon black suspension in water, adding octane to this suspension and mixing. Varying the conditions in the suspension modifies the hydrophilic/hydrophobic balance of the particles, making them partially wettable in both water and octane.  These particles then locate themselves at the oil-water interfaces after mixing, and stabilize the emulsion.  The fractal nature of these particles provides increased specific surface area that helps promote adsorption of low molecular weight polycyclic aromatic hydrocarbons from the octane.  At 0.015% w/w carbon black in the aqueous phase, cryo-SEM images reveal that the particles arrange into multiple layers at the octane water interfaces. We propose that this is a consequence of some carbon-black aggregation as the pH is lowered or salt concentration increased.  At 0.0075% w/w carbon black, stable emulsions are created with incomplete coverage at the oil-water interfaces. We monitor the zeta potential of these carbon black particles at various pH and salt concentrations, show specific ion binding, and relate the hydrophobicity of the particles to this potential.  When naphthalene, a model polycyclic aromatic hydrocarbon, is added to the octane, its partitioning into the aqueous phase is reduced dramatically from a control case with no carbon black. These particles have potential use for emulsifying crude oil subsequent to an oil spill.