Experimentally Testing a Generalized Coarsening Model for 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). While exact for a purely two dimensional foam with no liquid content this von Neumann law is increasingly violated for wetter quasi-2d foams. These latter foams have Plateau borders that are inflated with liquid and extend into the z-plane. Accounting for the size of the Plateau borders and gas that diffuses through both the Plateau Borders and thin films separating two bubbles, we modify von Neumann's law to a no-fit general coarsening equation where bubble size and shape now matter. 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 grow and others shrink - in direct violation of the usual von Neumann law but in agreement with our generalized version. We will show the coarsening of 6-sided bubbles and other violations of von Neumann's law for n-sided bubbles are driven predominantly by the bubble shape which is a key ingredient in our model.