Phase behavior of novel fluorinated surfactants in supercritical carbon dioxide

Abstract

A series of novel fluorinated analogues of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) surfactants, the sodium salt of bis(3,3,4,4,5,5,6,6,6-nonafluoro-1-hexanol) sulfosuccinate (CF₃(CF₂)₃CH₂CH₂OOCCH₂CH(SO₃Na)COOCH₂CH₂(CF₂)₃CF₃, di-HCF5), the sodium salt of bis(2,2,3,4,4,4-hexafluoro-1-butanol) sulfosuccinate (CF₃CFHCF₂CH₂OOCCH₂CH(SO₃Na)COOCH₂CF₂CFHCF₃, di-HCF3), the sodium salt of bis(2,2,3,3- tetrafluoro-1-propanol) sulfosuccinate (HCF₂CF₂CH₂OOCCH₂CH(SO₃Na)COOCH₂CF₂CF₂H, di-HCF2), and the sodium salt of bis(2,2,3,3,3-pentafluoro-1-propanol) sulfosuccinate (CF₃CF₂CH₂OOCCH₂CH(SO₃Na)COOCH₂CF₂CF₃, di-CF2), were synthesized and characterized by ¹H NMR, ¹³C NMR, ¹⁹F NMR and FT-IR spectroscopy, melting point, and elemental analysis. The pressure–temperature phase behavior for water-in-CO₂ microemulsions stabilized by the four surfactants was tested and the P–T diagrams were determined. In the phase behavior experiments, pressures up to 35 MPa, temperatures up to 65 °C, and water-to-surfactant molar ratios (W_o) from 10 to 30 were tested. The cloud-point pressure in microemulsions stabilized by the four fluorinated surfactants increased with increasing temperature, and at a fixed temperature, the cloud-point pressure increased with increasing W_o. However, the cloud-point pressure was only slightly affected by an increase in the concentration of surfactant at a settled W_o. The phase behavior for water-in-CO₂ microemulsions at different Cd(NO₃)₂ concentrations in the aqueous phase with the surfactant di-HCF5 was also determined, which is useful for the formation of CdS nanoparticles in our future studies.