[emim][etSO4] as the Polar Phase in Low-Temperature-Stable Microemulsions

Abstract

The authors demonstrate here that microemulsions with an ionic liq. as the continuous phase can be formed so that they are stable over a wide temp. range and have intermediary properties between flexible and stiff microemulsions. Three components (1-ethyl-3-methylimidazolium ethylsulfate ([emim][etSO4]), limonene, and octylphenol ethoxylate (Triton X100, abbreviated as TX-100)) were used. This ternary system was characterized from ambient temp. down to -10° by cond., viscosity, and small-angle x-ray scattering (SAXS) measurements. The SAXS data exhibit a characteristic single, broad scattering peak in conjunction with a typical q-4 decay at large q values. The SAXS data also were interpreted in terms of a dimensionless diln. plot, demonstrating that microstructures are neither isolated droplets nor a random flexible film structure but resemble molten liq. crystals (i.e., they are formed from locally cylindrical or planar structures). This semirigidity is attributed to a good match between the surfactant and the ionic liq.; this holds in a temp. range well <0°.