of surfactants. Zwitterionic surfactants are presently being This paper describes the adsorption of zwitterionic dodecylused in shampoos and as latex stabilizers. This paper reports N,N-dimethylammonio alkanoates with polymethylene interon the interfacial behavior of dodecyl-N,N-dimethylamcharge arms of different lengths on silica. The data presented were monio alkanoate surfactants on silica studied by time-reobtained by in situ ellipsometry, allowing time-resolved studies of solved ellipsometry. It is clear from our previous studies that the surface excess, the mean thickness, and the refractive index ellipsometry is a well-suited technique for studies of the of thin interfacial films. It is shown that the mode of adsorption interfacial behavior of surfactants at solid surfaces (8-10).
of zwitterionic surfactants is similar to that observed for ethylene-Not only does it provide information on fundamentally imoxide-based nonionic surfactants. The interaction energy between portant properties such as the surface excess, the mean layer single zwitterionic surfactants and silica is relatively weak and the adsorption process is best described in terms of surfactant self-thickness, and the refractive index, but it also allows moniassembly, promoted by the presence of the solid surface. The mode toring of these parameters with the relevant time resolution, of adsorption is only weakly affected by increasing the number thereby providing crucial information on the evolution of of intercharge methylene units. The surface aggregation behavior the adsorbed layer properties with time during the adsorption observed at the silica surface displays many parallels with the and desorption processes. Previous studies on nonionic surcorresponding solution phase behavior. Finally, the adsorption of factants have shown that the mean thickness of the adsorbed zwitterionic surfactants is relatively independent of the pH. Howlayer obtained by ellipsometry agrees well with thicknesses ever, as the pH is lowered to the p K a values of the terminal carobtained by neutron scattering and reflectivity, as well as boxyl group (i.e., as the surfactants become increasingly positively with light scattering and streaming-potential measurements charged) desorption is observed.