Foam films and liquid bridges formed by aqueous sodium naphthenate solutions

Sodium Naphthenates found in crude oils can act as surfactants and self-assemble in aqueous solutions to form micelles and liquid crystals. Understanding and controlling the drainage kinetics of thin films is an important problem that underlies the stability, lifetime and rheology of petroleum foams and emulsions. Here, we show that foam films formed by aqueous solutions of sodium naphthenates exhibit step-wise thinning or stratification. We utilize Interferometry, Digital, Imaging, Optical Microscopy protocols, previously developed by our group, to investigate the drainage and stratification in micellar foam films (< 100 nm) with high spatial (thickness < 10 nm) and temporal resolution (< 1 ms). We determine how the concentration of added sodium naphthenates influences the nanoscopic topography, stratification kinetics and step size of foam films. Finally, we show that visualization and analysis of capillary-driven thinning and pinch-off dynamics of the columnar neck in an asymmetric liquid bridge created by dripping-onto-substrate (DoS) of sodium naphthenate solutions can be used for characterizing the change in shear viscosity, extensional viscosity and microstructure in such surfactant solutions.