Evolution of grain boundaries in two-dimensional foam
The temporal evolution of disorder around grain boundaries between domains of ideally six-fold coordinated two-dimensional foam has been studied experimentally, using a foam comprising bubbles bridging between a soap solution and a cover glass. The disorder, quantified by the second central moment of the distribution of topological classes of the cells (µ2), generally increases. In certain cases, in which the evolution can be followed over longer times, µ2 eventually falls. This may be connected with the transient peaks for µ2 found in previous studies of relatively ordered soap froths. The absolute values of µ2 depend upon the boundary conditions imposed upon the foam, a rigid wall leading to higher values than a deformable boundary. The disorder about the grain boundaries propagates into the adjacent regions of ordered foam with constant speed, the roughness of the interface increasing with time.