Foam boosting by amphiphilic molecules in the presence of silicone oil

The effect of several surface active additives (called for brevity "foam boosters") on the foaming properties of solutions of the anionic surfactant sodium dodecyl polyoxyethylene-3 sulfate (SDP3S) is studied in the presence of silicone oil. As foam boosters we study lauryl amide propyl betaine (LAPB), lauryl acid diethanol amide (LADA), lauryl alcohol (LA), and a nonionic surfactant, which is;a glycerin derivative (denoted as Booster A). All these substances are used or have a potential to be used as commercial foam boosters in different formulations. The silicone oil is predispersed in the foaming solution in the form of micrometer-sized droplets, which act as foam breaking entities (antifoams). A set of several experimental methods is employed to clarify the main characteristics that are affected by the boosters. 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 LAPB 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 with the so-called entry, E, spreading, S, and bridging, B, coefficients of the silicone oil is observed. Optical observations of foam films show that the boosting effect cannot be explained by a reduced rate of the foam film thinning. Only the addition of LA leads to deceleration of the final stage of the film thinning process. The obtained results demonstrate that the various 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.