THE LIFETIME OF A COLLOID-SIZED GAS BUBBLE IN WATER AND THE CAUSE OF THE HYDROPHOBIC ATTRACTION

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 mechan ical (and physicochemical) stability is guaranteed when a bubble is cl osed with respect to the gaseous component. By assuming the diffusion of dissolved gas molecules away from a spherical gas bubble to determi ne the shrinkage rate, we calculate the lifetime of a bubble as a func tion of its size. Gas bubbles in the colloidal size range, with radii between 10 and 100 nm, have surprisingly short lifetimes, between abou t 1 and 100 mu s, whereas a mm-sized bubble can persist for months. Ou r results (which confirm and partwise extend the old calculations of E pstein and Plesset [5] [J. Chem. Phys., 18 (1950) 1505], indicate that the bridging bubble/cavity mechanism proposed earlier, can hardly pro vide the proper explanation of the long-ranged attraction force observ ed between hydrophobic surfaces immersed in water. (C) 1997 Elsevier S cience B.V.