Lecithin-rich mixtures of the nontoxic surfactants lecithin and Tween 80 are effective marine oil spill dispersants, but produce much higher oil-water interfacial tension than other, comparably effective dispersants. This suggests interfacial phenomena other than interfacial tension influence lecithin-Tween 80 dispersants’ effectiveness. The interface between seawater and dispersant-crude oil mixtures was studied using light microscopy, cryogenic scanning electron microscopy, and droplet coalescence tests. Lecithin:Tween 80 ratio was varied from 100:0 to 0:100 and wt% dispersant in the oil was varied from 1.25 to 10 wt%. Tween 80-rich dispersants cause oil-into-water spontaneous emulsification, while lecithin-rich dispersants primarily cause water-into-oil spontaneous emulsification. Possible mechanisms for this spontaneous emulsification are discussed, in light of images of spontaneously emulsifying interfaces showing no bursting microstructures, interfacial gel, or phase inversion, and negligible interfacial turbulence. Dispersant loss into seawater due to oil-into-water spontaneous emulsification may explain why Tween 80-rich dispersants are less effective than lecithin-rich dispersants with comparable interfacial tension, although longer droplet coalescence times observed for Tween 80-rich, self-emulsifying dispersant-oil mixtures may mitigate the effects of dispersant leaching. Conversely, surfactant retention in oil via lecithin-rich dispersants’ water-into-oil emulsification may explain why lecithin-Tween 80 dispersants are as effective as dispersants containing other surfactant blends which produce lower interfacial tension.
Bibliographical noteFunding Information:
The authors are grateful to Drs. Vijay John of Tulane University, Srinivasa Raghavan of University of Maryland, and Geoff Bothun of the University of Rhode Island for helpful discussions, and to Adriana Luna for tabulating particle diameters and droplet coalescence times. This work was supported in part by a grant from the Gulf of Mexico Research Initiative (GoMRI); by the Nanostructured Materials and Processes Program of the IPRIME industrial consortium at the University of Minnesota ; and by the University of Minnesota Undergraduate Research Opportunities Program . Data are publicly available through the Gulf of Mexico Research Initiative Information & Data Cooperative (GRIIDC) at https://data.gulfresearchinitiative.org/data/R5.x276.000:0001 ( http://dx.doi.org/10.7266/N7KW5D2D ). Parts of this work were carried out in the Characterization Facility, University of Minnesota, a member of the NSF-funded Materials Research Facilities Network ( www.mrfn.org ), via the MRSEC program.
- Crude oil
- Spontaneous emulsification