U. Florida, Lead: A. Chauhan
Our role in this project was to relate interfacial properties of carbon black and molecular dispersants to emulsion stability. We measured the interfacial properties including interfacial tension and elasticity to show that the carbon black covered interface has significant elasticity which leads to kinetically stable emulsions. We also showed that convection was required to get the particles to the interface likely due to the role of particle inertia. We also explored the interfacial tension dynamics and elasticity for Corexit. The dynamic interfacial tension data was used to determine the rate constants for adsorption and desorption, which may be very useful in designing an optimum spraying strategy for the dispersant when contacting an under-water oil plume. When compared to carbon black nanoparticles, Corexit 9500 is able to achieve significantly lower interfacial tensions at a 1-dodecene-water interface. It is therefore likely that Corexit 9500 would be able to break oil into smaller droplets with a smaller input of energy compared to carbon black. Interestingly, however, the interfacial elasticity for carbon black covered 1-dodecene-salt water interface is larger than for Corexit 9500. Therefore a combination of Corexit 9500 and carbon black may be able to break oil into smaller drops with a lower input of energy due to the Corexit and may create emulsions that are more stable over time due to carbon black.
U. Rhode Island, Lead: M.Levine
Our work on the GOMRI-funded project focused on the use of cyclodextrin-based systems for the removal of aromatic toxicants and toxicant metabolites from oil, the fluorescence-based detection of these toxicants, and the cyclodextrin-catalyzed detoxification of these compounds through their conversion to other organic moieties. We successfully demonstrated that a variety of cyclodextrin derivatives extract polycyclic aromatic hydrocarbons (PAHs) from oil sources including vegetable oil, motor oil, cod liver oil, as well as crude oil and tar balls collected directly from the Gulf of Mexico oil spill. We thoroughly investigated solvent effects and other system components so as to both optimize the system performance as well as to understand the fundamental science involved in this extraction process. We further demonstrated that once extracted, the aromatic toxicants participate in cyclodextrin-promoted energy transfer to a high quantum yield fluorophore, resulting in selective turn-on fluorescence in the presence of the toxicant of interest. This fluorescence-based detection was both highly sensitive for low concentrations of toxicants as well as highly selective in distinguishing structurally related toxicants with widely disparate toxicities. Finally, we demonstrated that cyclodextrin also catalyzes the conversion of a sample polycyclic aromatic hydrocarbon, 9-anthracenemethanol, to a non-planar maleimide-containing product. This disruption of planarity is expected to drastically decrease the toxicity of the PAH, through disrupting the ability of the PAH to intercalate in the DNA and form carcinogenic, covalent DNA adducts.
Brown University, Lead: A. Tripathi
Our work on the GOMRI-funded project focused on four aspects. 1) We studied the interaction of Alcanivorax borkumensis and octane in marine-like environments, specifically, the effect the bacteria has on the interfacial tension - and therefore stability - of the octane-seawater interface. We found that the bacteria metabolize oil at a rate that increases with time of suspension. 2) We investigated the effect of carbon black particles on the formation of oil-in-water emulsions of various distinct densities of crude oil (Light, medium, and heavy). 3) We probed the effect of interfacial area on the growth of oil-degrading bacteria. We also probed the effect of nutrient concentration on Alcanivorax Borkumensis growth. We discovered that increasing the bulk interfacial oil/water interfacial area, while keeping both the amount of bacteria and starting amount of oil constant, showed both a faster exponential growth rate as well as a higher peak amount of bacteria in solution. 4) We also built an experimental platform to quantitatively measure the transient growth of Alcanivorax borkumensis at the interface of oil and water. We used COREXIT EC9500A, Cetyltrimethylammonium bromide, Dioctyl sulfosuccinate sodium salt, L-a-Phosphatidylcholine, Sodium dodecyl sulfate, and Polysorbate 20 to investigate the impact of dispersants on Alcanivorax borkumensis. We assessed the impact of these dispersants on the growth rate, lag time, and maximum concentration of Alcanivorax borkumensis. The results of above studies are critical in the decision of dispersant use in the future.
U. Rhode Island, Lead: A. Bose
Our focus on this project was to demonstrate that surface functionalized carbon black particles could serve as benign dispersants for crude oil. The carbon black also served a dual role, absorbing polycyclic aromatic hydrocarbons from the oil, and reducing their transfer into the aqueous phase. Emulsions stabilized by carbon black and other dispersants have been exposed to Alcanivorax borkumensis and imaged using cryogenic scanning electron microscopy. Biofilms appear to form when the emulsion is stabilized by Tween-20, or carbon black, but they are not present when either Triton-X 100 or SDS was used as the emulsion stabilizers. Live/dead assays have also been performed to capture growth of Alcanivorax borkumensis upon exposure to emulsion droplets. Our work provides a ‘cradle-to-grave’ strategy for systematically evaluating the role of dispersants, not only focusing on their ability to disperse oil, but also following up with their effects on biodegradation.