Fluorescence study of the aggregation behavior of different surfactants in aqueous solutions in the presence and in the absence of gas

The effect of dissolved gas (air, argon, butane) on the properties of aqueous surfactant micelles (aggregation number, microviscosity and micropolarity) has been investigated by means of time-resolved fluorescence quenching and spectrofluorometry on a large number of surfactant systems differing by the nature of the surfactant (anionic, cationic, zwitterionic, and nonionic) and the temperature. The investigated properties were found to be independent of the state of the system: air-saturated, argon-saturated, or degassed. In the particular case of micellar solutions of cetyltrimethylammonium chloride, where the measurements involved 10 identical solutions, the average aggregation numbers measured for air-saturated, argon-saturated, and degassed solutions differed by less than 1%. The results indicate that if the hydrophobic interaction, which is the driving force for micelle formation, is affected by the dissolved gas, this would be to a very small extent, well below the sensitivity level of the methods of investigation of micellar solutions used in this study.