The solubility of gases in aqueous solutions of sodium 1-heptanesulfonate and sodium perfluorooctanoate

Abstract

Measurements have been made to determine the solubilities of oxygen, argon, methane, ethane, propane, and tetrafluoromethane at elevated pressures in aqueous solutions of sodium 1-heptanesulfonate and sodium perfluorooctanoate. The solubility of each gas follows Henry's law at all surfactant concentrations. In the case of sodium 1-heptanesulfonate, gas solubility data are obtained above and below the critical micelle concentration (CMC). Below the CMC, the solubility of each gas is approximately the same as that in pure water. Above the CMC, the solubility of each gas increases with surfactant concentration indicating micellar solubilization. Intramicellar solubilities of the various gases are calculated from this latter data for each surfactant. The intramicellar solubilities for the various gases dissolved in sodium 1-heptanesulfonate agree well with values predicted by the Laplace pressure model for micelles composed of surfactant ions having an alkyl chain length of seven carbon atoms. The 1-atm micellar solubilities of these same gases in sodium perfluorooctanoate are found to be considerably larger than those measured for sodium 1-heptanesulfonate, even though the alkyl chain lengths of the two surfactant anions are the same. The enhanced capacity for gas solubilization exhibited by the perfluorooctanoate micelles can be explained satisfactorily in terms of bulk properties of perfluorocarbon solvents using the Laplace pressure model.