Fluorocarbon-hydrocarbon gemini surfactant mixtures in aqueous solution

The aqueous solution properties of oppositely charged gemini-gemini surfactant mixtures have been studied with a combination of static surface tension, dynamic light scattering (DLS) and cryogenic transmission electron microscope (cryo-TEM) measurements. Two gemini surfactants were employed in this study: one is a partially fluorinated cationic gemini surfactant, 1,2-bis[dimethyl-(3-perfluorohexyl-2-hydroxypropyl)ammonium]ethane dibromide, and the other is a novel anionic gemini surfactant having hydrocarbon tail groups (N,N'-didodecyl-N,N'-dipropanesulfonylethylenediamine). Synergistic surfactant mixtures are frequently exploited to lower the mixed critical micelle concentration (cmc), however. such a decrease in the cmc is not observed in the current study. This suggests that limited mutual miscibility between the fluorocarbon and hydrocarbon tail groups plays a key role for the formation of the adsorbed layer, rather than attractive interactions such as electrostatic forces. On the other hand, spontaneous formation of vesicle-like molecular aggregates is suggested to occur as a result of their synergistic interaction in bulk solution. (C) 2008 Elsevier B.V. All rights reserved.