Synergism in binary mixtures of surfactants. 7. Synergism in foaming and its relation to other types of synergism

The relationship between synergism in Ross‐Miles foaming and the existence of other types of synergism in binary mixtures of surfactants has been investigated. All studies were conducted in solutions of constant ionic strength (0.1 M NaCl) at 25 and/or 60 C. Six anionic‐zwitterionic or anionic‐nonionic mixtures and a sodium dodecylbenzenesulfonate (LAS)‐soap mixture, all consisting of commercial surfactants, were studied. Synergism in foaming effectiveness, measured by initial foam heights, appears to be related to synergism in surface tension (γ) reduction effectiveness, but not to synergism in γ reduction efficiency or in mixed micelle formation. The LAS‐soap system showed negative synergism in foaming effectiveness, correlated with negative synergism in γ reduction effectiveness, the conditions for which are defined. There appears to be no correlation between synergism in foaming efficiency and synergism in either γ reduction efficiency or mixed micelle formation. There also appears to be no unambiguous relationship between foam stability, measured by the ratio of the 5‐minute to the initial foam height, and the average area per surfactant molecule at the aqueous solution/air interface.