Physicochemical approach to nanobubble solutions

Small bubbles of nitrogen, methane, or argon with an average radius of 50 nm, as measured by scanning electron microscopy, were prepared under atmospheric conditions. The lifetime of the nanobubbles extended to more than two weeks. The total amount of gases in the nanobubble solutions reached 600 cm3 per 1 dm3 of water, and the liquid density was about 0.988 g/cm3. The internal pressure of the nanobubbles was estimated to be 6 MPa. The number of nanobubbles was 1.9×1016 bubbles per 1 dm3 of water. These findings show that almost no gas samples are dissolved homogeneously in the aqueous solution and that the vast majority is present in the form of nanobubbles, that is, nanobubbles should be thermodynamically unstable. Attenuated total reflectance infrared spectroscopy showed that the surfaces of the nanobubbles contain hard hydrogen bonds that may reduce the diffusivity of gases through the interfacial film.