Phase behavior and structure of sodium napthenate micelles

The formation and stability of petroleum foams and emulsions can sometimes be attributed to sodium naphthenates surfactants. 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. In this study, we develop a comprehensive understanding of the phase behavior of sodium naphthenate micelles (including size, shape and inter-micellar interactions) through a combination of static and dynamic scattering measurements. Small-angle X-ray scattering (SAXS) measurements revealed intriguing trends – micelle shape and size varied with increasing surfactant concentrations in the dilute (<5 wt%) limit. At higher concentrations (5 wt% – 40 wt%), while the micelle shapes and sizes remained largely invariant, inter-micellar interactions became increasingly significant, leading to stronger structure factor contributions to scattering intensities. These concentration-dependent trends are contrasted against trends in hydrodynamic size and zeta-potential of the micelles from dynamic light scattering measurements, as well as stratification kinetics of foams containing sodium naphthenate micelles.