Effect of oil on stability and properties of aqueous nanobubbles: Experiments and molecular dynamics simulations

Nanobubbles (NBs) are used in many applications involving organic matter, including removal of hydrocarbon from water and sands, and enhancement of oil recovery. Therefore, the impact of oil on the stability and properties of aqueous NBs is of utmost importance. Furthermore, coating of NB surfaces with organic matter such as oil has been proposed as one of the mechanisms for elusive NB stabilization. We hypothesize that a small amount of oil stabilizes the NBs, but bulk oil causes NB dissolution due to higher solubility of the gas in oil.

The effect of oil on NB properties was probed experimentally by nanoparticle tracking analysis (NTA) and interfacial tension (IFT) measurements. Molecular dynamics (MD) simulations were used to uncover the underlying mechanisms of oil-NB interactions.

Experimentally, addition of oil causes NB decay, and NBs lower the water-oil IFT. The MD simulations suggest that small amounts of oil associate with the NB, causing increase in the NB size and reduction of the IFT and internal pressure. Oil layers, on the other hand, cause NB destruction either by reducing the aqueous gas saturation, or causing the bubbles to burst upon contact. The simulations also predict lower IFT with oil containing dissolved N₂, consistently with experiments.