Foaming properties of mixtures of a non-ionic (C12DMPO) and an ionic surfactant (C12TAB)

An extensive study of the foaming properties of a surfactant mixture consisting of the non-ionic dodecyldimethyl phosphineoxide (C(12)DMPO) and the cationic dodecyltrimethyl ammonium bromide (C(12)TAB) with mixing ratios of C(12)DMPO:C(12)TAB = 1:0, 50:1, 1:1, 1:50, 0:1 is performed both above and below the critical micelle concentration. Foamability and foam stability were examined using the commercially available FoamScan (sparging), the standardised Ross-Miles (pouring) and a home-built winding (shaking) technique. The focus, however, was on FoamScan measurements as they allowed for the evaluation of the foam's liquid content. The foamability and foam stability of C(12)TAB was found to be larger than that of C(12)DMPO. The foamability continually increased with increasing C(12)TAB content in the surfactant mixture, which reflects the reduction of the diffusion relaxation time (i.e. faster adsorption). Where possible correlations are drawn between the foam properties on the one hand and adsorption and foam film properties on the other hand, which were studied previously. Interestingly, the 1:1 mixture shows weak/negligible surfactant interactions but--counterintuitively--an increased foam stability compared to the single surfactant systems. However, at this ratio charge neutralization occurs, which leads to the formation of a Newton Black Film thus suggesting that the foam film type plays an important role in the foam stability.