A disjoining pressure study of foam films stabilized by mixtures of a nonionic (C12DMPO) and an ionic surfactant (C12TAB).

This work is a continuation of a previous study [Langmuir 23 (2007) 5315-5323] of aqueous foam films stabilized by surfactant mixtures consisting of a cationic and a nonionic surfactant. In both studies a thin film pressure balance was used to investigate the disjoining pressure Pi as a function of the film thickness h. With the resulting Pi-h curves the surface charge densities q(0) of the foam films were determined by fitting them with the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Our previous study demonstrated that mixing the nonionic surfactant beta-dodecylmaltoside (beta-C(12)G(2)) and the cationic dodecyl trimethylammonium bromide (C(12)TAB) allows one to tune q(0) and thus the type of foam film. In the present study the nonionic surfactant dodecyldimethyl phosphineoxide (C(12)DMPO) instead of beta-C(12)G(2) was used and C(12)DMPO/C(12)TAB mixtures in a concentration range from 0.1 to 2.0 cmc were studied at mixing ratios of C(12)DMPO:C(12)TAB = 1:0, 50:1, 1:1, 1:50, 0:1. The results are compared with those of the beta-C(12)G(2)/C(12)TAB mixture and are discussed in terms of surface charge densities.