Fluorine-free and hydrophobic room-temperature ionic liquids, tetraalkylammonium bis(2-ethylhexyl)sulfosuccinates, and their ionic liquid-water two-phase properties

Fluorine-free and hydrophobic room-temperature ionic liquids (RTILs) composed of the bis(2-ethylhexyl) sulfosuccinate (BEHSS) ion, which is known as the surface-active anion constituting Aerosol OT(R), and symmetric tetraalkylammonium ions ((CnH2n+1)(4)N+; n = 4 - 8), have been prepared. Physicochemical properties of the water-saturated RTILs such as density, conductivity, viscosity and mutual solubility with water ( W) have been measured. The RTIL|W interface is polarizable for the RTILs with n = 5 - 8 in spite of the high water content, 3.6 - 8.9 wt% in the water-saturated RTILs. The width of the polarized potential window of the RTIL|W interfaces is quantitatively correlated with the solubility of the RTIL in W. The RTIL - W two-phase systems are not spontaneously emulsified and no reverse micelles are formed in the water-saturated RTILs, although BEHSS 2 is known to form stable water-in-oil emulsions and reverse micelles in oil - water two-phase systems.