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 exper imentally, using a foam comprising bubbles bridging between a soap solution and a cover glass. The disorder, quantified by the second central moment o f the distribution of topological classes of the cells (mu(2)), generally i ncreases. In certain cases, in which the evolution can be followed over lon ger times, mu(2) eventually falls. This may be connected with the transient peaks for mu(2) found in previous studies of relatively ordered soap froth s. The absolute values of mu(2) depend upon the boundary conditions imposed upon the foam, a rigid wall lending to higher values than a deformable bou ndary. The disorder about the grain boundaries propagates into the adjacent regions of ordered foam with constant speed, the roughness of the interfac e increasing with time.