Experimentally Testing the Border-Crossing Model for Coarsening of Quasi-Two-Dimensional Wet Foams

In dry foams, a bubble’s area grows or shrinks according only to its number of sides, dA/dt=K₀(n-6). This von Neumann law is increasingly violated for wetter foams, where Plateau borders are inflated with liquid and this has been assumed to block the available film area across which gas diffuses. Recently it was predicted that a surprisingly large amount of gas actually crosses the borders, and that this modifies the von Neumann law such that bubble size and shape now matter [1]. To test this experimentally, we measure the growth rate of individual bubbles in quasi-2d foams of variable wetness confined between parallel plates. Interestingly, some 6-sided bubbles are found to grow, and others are found that shrink -- in violation of the usual von Neumann law. These results, and similar data for bubbles with other numbers of sides, appear to agree with the generalization of the von Neumann law that incorporates the effects of border crossing [1].

[1] C. D. Schimming and D. J. Durian, "Border-Crossing Model for the Diffusive Coarsening of Two-Dimensional and Quasi-Two-Dimensional Wet Foams," Phys. Rev. E 96, 032805 (2017). http://dx.doi.org/10.1103/PhysRevE.96.032805