The solubility of carbon dioxide and nitrous oxide in aqueous solutions of cetyltrimethylammonium bromide, sodium dodecyl sulfate, sodium 1-heptanesulfonate, and sodium perfluorooctanoate

Abstract

Measurements have been made to determine the solubilities of carbon dioxide and nitrous oxide in aqueous solutions of cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), sodium 1-heptanesulfonate (SHSo), and sodium perfluorooctanoate (SPFO) at elevated pressures. The solubilities of each gas, measured at 26°C for solutions of CTAB and at 25°C for the other surfactants, follow Henry's law at all surfactant concentrations. Two distinctly different types of behavior are exhibited by SHSo. At concentrations below the critical micelle concentration (CMC), the addition of SHSo acts to suppress the solubility of CO 2, while at higher concentrations, the opposite behavior is observed in that addition of SHSo results in an increase in CO 2 solubility. The CMC values for the other surfactants are all much lower than that for SHSo. As a result, the solubility data for N 2O and CO 2 in these surfactants are all taken at concentrations in excess of the CMC and in every case, the addition of surfactant is found to enhance gas solubility. The increase in gas solubility observed above the CMC for each of the four surfactants is found to be a linear function of surfactant concentration as expected for micellar solubilization. The intramicellar solubilities of CO 2 and N 2O calculated from these latter data do not correlate well with solubilities of other nonpolar gases but rather are displaced toward higher concentrations, thus suggesting that the hydrophilic character of these two gases leads to enhanced solubilization.