Experiments on defect spreading in hexagonal foams

Defects were introduced in a hexagonal liquid foam prepared by a novel technique and their coarsening was observed. Both isolated defect clusters, with and without dislocation character, and grain boundaries were produced. As the defects coarsen, a gradient of cell size develops along the direction of growth. Differences in the growth characteristics of isolated defects were found, depending on whether the average size of the cells in the defect clusters is larger (type I) or smaller (type II) than the size of the surrounding honeycomb cells. Clusters of type I show an approximately linear increase of diameter with time, while clusters of type II have an initial contraction. The evolution to the scaling regime of a honeycomb containing a distribution of type I clusters is discussed.