Do stable nanobubbles exist in mixtures of organic solvents and water?

Several recent papers have described the existence of stable nanobubbles in bulk, which is surprising given that the high curvature of these bubbles is expected to place such bubbles under a high pressure and therefore lead to rapid dissolution. Here, we investigate the possible existence of nanobubbles in mixtures of water plus an organic solvent using both static and dynamic light scattering and infrared spectroscopy. The mixing of solvents was designed to introduce nanobubbles into bulk solution via supersaturation of the solution. The solutions scatter light for a long period (days) after mixing, which is consistent with the formation of nanoscale objects, but we show that these scattering objects originate from water-insoluble impurities in the organic solvents. Our results are inconsistent with the presence of gas nanobubbles in bulk solution: Degassing the solutions, either before or after mixing, has a minimal effect on the scattering, and purification of the organic solvent before mixing reduces the scattering after mixing. Therefore, previous reports of nanobubbles based on scattering experiments should be reconsidered with the hypothesis that the scattering objects are not actually gaseous.