Foam boosting by amphiphilic molecules in the presence of silicone oil

The effect of several surface active additives (called for brevity "foam bo osters") on the foaming properties of solutions of the anionic surfactant s odium dodecyl polyoxyethylene-3 sulfate (SDP3S) is studied in the presence of silicone oil. As foam boosters we study lauryl amide propyl betaine (LAP B), lauryl acid diethanol amide (LADA), lauryl alcohol (LA), and a nonionic surfactant, which is;a glycerin derivative (denoted as Booster A). All the se substances are used or have a potential to be used as commercial foam bo osters in different formulations. The silicone oil is predispersed in the f oaming solution in the form of micrometer-sized droplets, which act as foam breaking entities (antifoams). A set of several experimental methods is em ployed to clarify the main characteristics that are affected by the booster s. Foam tests shaw that LADA and Booster A enhance mainly the foaminess of the solutions and that LA improves mainly the foam stability, whereas the L APB increases both. The enhanced foam stability in the presence of LAPB and LA correlates well with the higher barriers to oil drop entry, measured by the film trapping technique (FTT). No correlation of the film stability wi th the so-called entry, E, spreading, S, and bridging, B, coefficients of t he silicone oil is observed. Optical observations of foam films show that t he boosting effect cannot be explained by a reduced rate of the foam film t hinning. Only the addition of LA leads to deceleration of the final stage o f the film thinning process. The obtained results demonstrate that the vari ous boosters affect different characteristics of the foaming solution, and which of the additives is appropriate for a particular application depends strongly on the time-scale of interest.