Bubble dynamics relaxation in aqueous foam probed by multispeckle diffusing-wave spectroscopy.

We study the bubble rearrangement dynamics in aqueous foam during the passage from liquidlike to solidlike behavior which follows a transient shear deformation that perturbs the bubble packing. The local dynamics is probed using multispeckle diffusing-wave spectroscopy. We show that following the perturbation the average time between rearrangements relaxes exponentially, with time elapsed since the end of the perturbation. The observed scaling of the characteristic relaxation time with perturbation amplitude and foam age is explained by a schematic coarse-grained model based on the scaling state hypothesis.