The surface viscosity of detergent solutions as a factor in foam stability

Abstract

A rotational viscometer, capable of providing theological data for surface films on solutions of surface active agents, has been developed and is described in detail. Surface viscosity data have been obtained with a group of detergents and detergent mixtures specially selected to illustrate the role of surface viscosity in the stability of the foams obtained from the solutions by beating. Foams of highest stability appear to be produced from solutions showing appreciable surface viscosity; solutions yielding foams of very poor stability show very low surface viscosity. Some foams of intermediate stability which rapidly become thin and tenuous, although relatively persistent in total volume, appear as exceptions to the rule. It is suggested that the change in specific surface, in addition to the change in foam volume, with time is necessary to characterize properly the processes taking place. Finally, it is suggested that detergents yielding foams of high foam stability consist of two or more compounds, one of which has high solubility and provides a reservoir of surface active material of poorly developed coherence; and the other of which, though much lesser in amount and also less soluble, provides the necessary coherence in the mixed surface film.