Inter-bubble gas diffusion in liquid foam

Ostwald ripening (disproportionation) of gas–liquid foam is a process in which large bubbles grow at the expense of small bubbles because pressure differences drive inter-bubble gas diffusion. The rather overlooked theory of Robert Lemlich, for relatively wet foam, is revisited and its analogy with Ostwald ripening of metals grains discussed and this is put into context with recent advances. Lemlichʹs Theory assumes that the rate of disproportionation is governed by gas mass transfer, whereas recent work has suggested that it may be mechanically resisted by contraction/expansion of gas–liquid interfaces. In addition, the exact generalisation of the von Neumann Theory of grain growth to three dimensions is made quantitatively relevant to dry foams. Developments in tomographies and other experimental techniques have the potential to enable this model to be verified.