Electrosorption from pseudobinary surfactant mixtures: I. Binary surfactant mixtures of strongly and weakly adsorbable components investigated by AC polarography

Abstract

The adsorption of pseudobinary surfactant mixtures was studied by AC polarographic differential capacity-potential measurements. Strongly adsorbable surfactants (octaethylene glycol dodecyl ether, cetylpyridinium chloride, and sodium undecylsulfonate) were used in this study as well as weakly adsorbable surfactants (i-butanol, n-butanol, hexahydrophenol, and triethylamine hydrochloride). For the mixtures of strongly adsorbable surfactants it could be shown that the C d E curves can exhibit two ad-/desorption maxima corresponding to the ad-/desorption of the single surfactants. However, their mutual dependence shows that a surfactant concentration analysis is possible only in a very limited concentration range. In order to determine the composition of the mixed adsorption layer, weakly adsorbable surfactants such as model systems were used. The possibilities and limitations of double layer capacity measurements for a quantitative evaluation are outlined. The concentration analysis is possible when a mixture of a strongly adsorbable surfactant with a weakly adsorbable surfactant is considered. Also, mixtures of two strongly adsorbable surfactants can be analyzed provided that their surface activities and the potentials of maximum adsorption are different. The double layer capacity-potential curves in the presence of two weakly adsorbable surfactants give only qualitative information on their mixing behavior in the surface phase. It is impossible to determine the surfactant concentrations in these mixtures.