Size distribution of decaying foam bubbles.

The most studies on the stability of foam bubbles investigated the mechanical stability of thin films between bubbles due to the drainage by gravity. In the current work, we take an alternative approach by assuming the rupture of bubbles as a series of random events and by investigating the time evolution of the size distribution of foam bubbles over a long time up to several hours. For this purpose, we first prepared layers of bubbles on Petri dishes by shaking soap solutions of a few different concentrations, and then we monitored the Petri dishes by using a time-lapse video imaging technique. We analyzed the captured images by custom software to count the bubble size distribution with respect to the initial concentration and elapsed time. From the statistics on our data, we find that the total bubble volume decreases exponentially in time, and the exponent, i.e., the mean lifetime, is a function of the bubble size. The mean lifetimes of larger bubbles are observed to be shorter than those of smaller bubbles, by approximately a factor of 2.