Effect of Sodium Halides on the Surface Structure of Foam Films Stabilized by a Nonionic Surfactant

The effect of sodium halides on the surface structure of foam films stabilized by the nonionic surfactant dodecyldimethyl phosphine oxide (C₁₂DMPO) was investigated using a combination of neutral impact collision ion scattering spectroscopy and thin film pressure balance. The former technique was used to determine the concentration depth profiles of the elements at the liquid surface, while the latter technique was used to provide film thickness information. An excess of iodide was found at the liquid surface in the presence of C₁₂DMPO. Upon formation of the foam film, iodide was shifting closer to the surface showing that the foam film surface is more negatively charged than the surface of the respective bulk liquid. In contrast, an excess of chloride was found at the surface only in the presence of the surfactant and formation of a foam film. The iodide-containing films were slightly thicker than the chloride-containing films, which is concluded to be due to the increased surface charge of the iodide-containing films.