A NEW METHOD TO ESTIMATE THE STABILITY OF SHORT-LIFE FOAMS

In classical foam stability studies, foam height variation is monitore d versus time. The decay pattern depends, however, upon the foam struc ture at the start of the decay; in many instances this structure chang es significantly during the first few minutes, and it is difficult to select a proper ''zero time'' of decay. We have found that the decay b ehavior is very well defined when the original state of the foam is ta ken as the equilibrium state of the classical Bikerman's experiment, i .e. when the foam formation by bubbling (at the bottom of the column) exactly compensates the foam collapse (at the top). It is found that u nder such starting conditions, short life foam decay exhibits a linear variation in the foam column height with the logarithm of the elapsed time. A dimensionless H vs. log t plot exhibits the same features for different systems; thus, both a characteristic height and a character istic time can be extracted from the experimental data, the latter bei ng readily related to the foam stability. These parameters are used to quantify the effect of additives on the decay of several foam systems containing nonionic and anionic surfactants.