Relation between ionic surfactant concentration and thickness of foam film stabilized by ionic-nonionic surfactant mixed adsorbed films

In this paper, we compared the thickness of common black films stabilized by four different ionic-nonionic surfactant mixed adsorbed films. For the cetyltrimethylammonium chloride (CTAC) - pentaethyleneglycol monododecyl ether (C12E5), SDS - tetraethyleneglycol monodecyl ether (C10E4), and dodecyltrimethylammonium bromide (DTAB) - tetraethyleneglycol monooctyl ether (C8E4) systems, the foam film thickness measured by using Scheludko-Exerowa glass ring method coincided very well when the foam film thickness was plotted as a function of bulk ionic surfactant (1:1 electrolyte) concentration. In addition, by using the phase diagram of mixed adsorbed film obtained from the thermodynamic analysis of the surface tension data, it was also demonstrated that the surface charge density and surface tension have a minor effect on the equilibrium film thickness. On the other hand, the foam film stabilized by the 1-decyl-3-methyl imidazolium tetrafluoroborate (DMIMBF4) - C10E4 mixed adsorbed film showed much smaller thickness values compared to the above-mentioned systems. Irregular behavior observed in the DMIMBF4 - C10E4 system was discussed based on the specific interaction between imidazolium head groups and BF4- ions through hydrogen bonding in an ionconcentrated environment in the Stern layer.