(750b) Surfactant Transport, Interfacial Rheology, and Film Drainage of a Model Oil-Dispersant-Aqueous System

Oil spills in marine environments continue to demonstrate the lack of basic information available for effective disaster response.  Specifically, surfactant dispersants are deployed at both the sea surface and at leaking well heads; these are two situations that represent different, and often untested, conditions for dispersant use.  Variables that have not been characterized include high temperature gradients, large pressures, convection, and rapid dispersant concentration changes. Understanding surfactant transport phenomena to the oil-aqueous interface is imperative to the decision-making process of when and where surfactant dispersants should be applied.  In this work, we develop a model surfactant-oil-aqueous system using Tween-80 (a primary component in Corexit® dispersant), squalane, and both simulated sea water (SSW) and deionized water (DI) to investigate transport phenomena and interfacial mechanics, which impact system stability and the lifetime of an emulsion.  We use a microtensiometer^[1] to study the importance of convection, rapid bulk concentration changes, and interfacial mechanics of an oil-aqueous interface.  We are able to measure the dynamic interfacial tension as surfactant adsorbs to an initially clean oil-aqueous interface, and we are able to remove the bulk surfactant at different points in the dynamics by rinsing the interface and continuously replacing the bulk fluid with surfactant-free aqueous phase.  A critical interfacial tension arises that links the transport dynamics to the onset of partial reversibility in the system.  By measuring the mechanical properties of pre-rinsed and rinsed interfaces, we also find a critical interfacial tension that leads to changes in the elasticity of the interfaces.  This interfacial tension correlates well with the critical interfacial tension that indicates the onset of partial reversibility.  To determine the effects of interfacial elasticity and concentration changes on the stability of an emulsion, we bring two surfactant-coated interfaces into contact and monitor coalescence times and initial droplet shape profiles.  We discuss these coalescence results in the context of film drainage, and as drainage time relates to the elasticity of the contacted interfaces. 

1.            Alvarez, N.J., L.M. Walker, and S.L. Anna, A microtensiometer to probe the effect of radius of curvature on surfactant transport to a spherical interface. Langmuir, 2010. 26(16).