TRANSIENT FOAMING BEHAVIOR OF AQUEOUS ALCOHOL-SOLUTIONS AS RELATED TOTHEIR DILATIONAL SURFACE-PROPERTIES

The foamability of aqueous alcohol solutions can be measured by contin uously sparging air in a closed loop through the solution under standa rd conditions, The amount of foam produced in the steady state is take n as a measure for the foamability. Aqueous alcohol solutions show tra nsient foaming behavior, This can be explained by assuming that, due t o lack of disjoining pressure, thin aqueous alcohol films collapse whe n due to drainage a critical film thickness has been reached, This mea ns that the drainage rate of these films determines to a large extent the lifetime of these films. Film drainage can be slowed down by surfa ce tension gradients opposing the liquid flow in the film. The ability of aqueous alcohol solutions to generate a surface tension gradient c an be measured by means of the overflowing cylinder technique. By chan ging the alcohol concentration for ethanol, l-butanol, 1-hexanol, and l-octanol it is found that both the foamability and the ability to gen erate a surface tension gradient pass over a maximum value at an alcoh ol concentration which is characteristic for the alcohol considered. T his alcohol concentration coincides with the alcohol content at which a maximum in the ability to generate a surface tension gradient is fou nd. It is concluded that the transient foaming behavior of these aqueo us alcohol solutions is mainly determined by their ability to generate a surface tension gradient. (C) 1996 Academic Press, Inc.