(144d) Phase Behavior, Micelle Structure and Stepwise Drainage of Aqueous Sodium Naphthenate Foam Films

Sodium naphthenates are surfactants found in crude oils that self-assemble in aqueous solutions to form micelles and liquid crystals. Understanding and controlling the drainage kinetics of thin aqueous sodium naphthenates films is an important problem that underlies the stability, lifetime and rheology of petroleum foams and emulsions. However, relatively little information is available about the sizes and shapes of self-assembled structures formed by sodium naphthenates, limiting our ability to control foam or emulsion stability and the success of sequestration or extraction processes. Here, we present direct comparisons between the phase behavior of aqueous solutions of sodium naphthenates, the structure of sodium naphthenate micelles in such aqueous solutions, and the film drainage behavior. We elucidate the influence of sodium naphthenate concentration on the nanoscopic topography, stratification kinetics and step size of foam films, as determined through interferometry, digital imaging and optical microscopy protocols, and contrast the results with the trends in size, shape and inter-micellar interactions revealed through a combination of small-angle X-ray scattering (SAXS) and dynamic light scattering measurements. These trends will be categorized in surfactant concentrations regimes including dilute concentration regimes wherein micelle shape and size vary with increasing surfactant concentrations and moderate concentration regimes wherein the micelle shapes and sizes remained largely invariant while inter-micellar interactions became increasingly significant.