The lifetime of a colloid-sized gas bubble in water and the cause of the hydrophobic attraction

Abstract

When considered to be open in the thermodynamic sense with respect to the enclosed gas, bubbles that are present in a liquid bulk phase are unstable in all respects and tend to dissolve. Conversely, full mechanical (and physicochemical) stability is guaranteed when a bubble is closed with respect to the gaseous component. By assuming the diffusion of dissolved gas molecules away from a spherical gas bubble to determine the shrinkage rate, we calculate the lifetime of a bubble as a function of its size. Gas bubbles in the colloidal size range, with radii between 10 and 100 nm, have surprisingly short lifetimes, between about 1 and 100 μs, whereas a nm-sized bubble can persist for months. Our results (which confirm and partwise extend the old calculations of Epstein and Plesset [5] [J. Chem. Phys., 18 (1950) 1505], indicate that the bridging bubble/cavity mechanism proposed earlier, can hardly provide the proper explanation of the long-ranged attraction force observed between hydrophobic surfaces immersed in water.