Lauryl alcohol and amine oxide as foam stabilizers in the presence of hardness and oily soil

The effects of two potential foam boosters, n‐dodecanol (or lauryl alcohol: LA) and tetradecyldimethylamine oxide (C14DMAO), were investigated for two situations in which foam made from a 0.01 wt% solution of a common alkylethoxy sulfate surfactant was highly unstable in the presence of oil drops consisting of an n‐hexadecane/oleic acid mixture. In one case in which dissolved CaCl2 was present at alkaline pH, insoluble calcium oleate particles formed in situ and facilitated foam breakage. In the other, a much higher concentration of calcium was present at neutral pH, and drops of a microemulsion phase formed but no calcium oleate. In both cases, 0.005 wt% LA reduced the entry coefficient, E, of the oil to the air‐water surface sufficiently to prevent drop entry and stabilized the foam. In contrast, 0.005 wt% C14DMAO caused smaller reductions in E and was ineffective as a foam booster. LA was more effective because it was able to form a more compact monolayer with the surfactant than C14DMAO at the air‐water surface, which led to lower surface tensions and hence lower values of E.