Simple and generally applicable method of determination and evaluation of foam properties

A new, simple foam test, in which a well-controlled volume of gas is introduced into a definite volume of solution, is presented along with the method of analysis. Aqueous solutions of sodium dodecyl sulfate (SIDS), n-octyl-beta-D-glucopyranoside, hexadecyltrimethylammonium bromide (CTAB), and n-hexanol, i.e., four systems forming metastable and transient foams, were studied. The parameter R5, defined as the ratio of the height of the foam at 5 min after formation to the initial height, is proposed for the evaluation of foam stability. Foams having R5 values higher than 50% can be considered as metastable. Lower R5 values indicate low-stability foams. Changes of R5 values with concentration are similar to those of foam half-life with concentration. Thus, instead of measurements lasting hours for the foam half-life, one can obtain similar information from tests lasting only a few minutes. With this test also one can obtain information about the solution contents in foams. This parameter can be used as an additional criterion for the evaluation of foam stability. In the case of metastable foams formed by SDS, CTAB, and n-octyl-beta-D-glucopyranoside, the initial foam volume was almost equal to the volumes of the dispersed gas and the solution carried into the foam by the bubbles. This shows that there was practically no rupture of foam films at the stage of the foam formation.