Coarsening of two-dimensional foams confined by walls.

A finite two-dimensional (2D) foam sample bounded by walls contains inner bubbles (I-bubbles) and peripheric or edge bubbles (E-bubbles). We derive equations for the rate of area change of both types of bubbles, which depend linearly on the number of neighbours of a bubble but are, in general, not scale independent. From these equations we obtain global kinetic laws for the two aggregates (I- and E-) of bubbles. The topological operations that occur during coarsening of E-bubbles are identified and the effect of curvature of the wall on coarsening is discussed. Experimental results obtained with 2D (monolayer) foams are presented which, combined with theory, give a reasonable picture of the effect of boundaries on foam coarsening. A disturbance due to the bounding walls was not experimentally detected: I- and E-bubbles were found to grow in pace, their average areas remaining equal, with a global parabolic growth law. However, this property could not be inferred from the growth equations for individual I- and E-bubbles. [ABSTRACT FROM AUTHOR]