Coarsening of two-dimensional foams confined by walls

A finite two-dimensional (2D) foam sample bounded by walls contains inner b ubbles (I-bubbles) and peripheric or edge bubbles (E-bubbles). We derive eq uations 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 s cale independent. From these equations we obtain global kinetic laws for th e two aggregates (I- and E-) of bubbles. The topological operations that oc cur during coarsening of E-bubbles are identified and the effect of curvatu re of the wall on coarsening is discussed. Experimental results obtained wi th 2D (monolayer) foams are presented which, combined with theory, give a r easonable picture of the effect of boundaries on foam coarsening. A disturb ance due to the bounding walls was not experimentally detected: I- and E-bu bbles were found to grow in pace, their average areas remaining equal, with a global parabolic growth law. However. this property could not be inferre d from the growth equations for individual I- and E-bubbles.