Coarsening of two-dimensional soap froths in the presence of pinning centers

We have studied experimentally the coarsening of two-dimensional soap froths in the presence of pinning centers. When the average bubble size is smaller than the average interpin distance, the growth is unaffected. When both dimensions become comparable the froth enters a crossover regime followed by a pinned state where growth stops. The nature of the long-time configurations depends strongly on the size of the pins relative to the size of the plateau borders. For thick pins, the final configurations consist of combinations of Steiner trees of small numbers of points with pins located at vertices of the film network. For thin pins the final average bubble size is larger than in the case of thick pins and the final configurations are much more varied. Qualitatively similar behavior is observed in grain growth in metals with impurities.