Microemulsion Formation in 1,1,1,2-Tetrafluoroethane (R134a)

Water solubilization by anionic perfluorinated surfactants has been examined in the condensed phase of the hydrofluorocarbon (HFC) gas 1,1,1,2-tetrafluoroethane (R134a) in the temperature range 15−55 °C and to pressures of 500 bar. The surfactant di(1 H,1 H,5 H -octafluoro- n -pentyl) sodium sulfosuccinate (di-HCF4) forms stable water-in-R134a microemulsions up to w > 60 (where w = [H 2 O]/[surfactant]) with applied pressure and to w = 50 at the vapor pressure of R134a. Solubilization levels for the related surfactant di(1 H,1 H,5 H -octafluoro- n -pentyl) ammonium phosphate and the commercial grade anionic perfluoro poly(propylene oxide) carboxylate (CF 3 (CF 2 CF(CF 3 )−O−) 3 CF 2 CO 2 - NH 4 + ) were lower. Structural features of the microemulsion systems formed have been examined by small-angle neutron scattering (SANS). The SANS data from all microemulsions examined were characteristic of spherical droplet structure and provided measurement of the mean radius and, for di-HCF4, the headgroup area at the water−R134a interface. When significant, attractive interactions between droplets were evident in the S ( Q ) ATT contribution to the SANS I ( Q ). The low level of this contribution for di-HCF4 confirmed the good compatibility of this surfactant with R134a under the conditions examined.