Phase behavior and microstructure of the system consisting of 1-butyl-3-methylimidazolium hexafluorophosphate, water, triblock copolymer F127 and short-chain alcohols

The phase behavior and microstructure of the system consisting of ionic liquid BmimPF6, copolymer F127, H2O and short-chain alcohols including ethanol, n-propanol or n-butanol were investigated at 30 °C. Large areas of single-phase microemulsion were observed in all the three systems. Specially, lyotropic liquid crystal appeared in the n-butanol system while it disappeared when the other two alcohols were used. The water-in-BmimPF6, bicontinuous, and BmimPF6-in-water regions of the microemulsions were identified by the usual electrical conductivity measurement. As an attempt, UV-vis spectroscopy was successfully used to distinguish different type of microemulsions using methyl orange as solvatochromic probe. Furthermore, dynamic light scattering (DLS) measurements were also skillfully introduced to vividly track the structural variation of different microemulsions. On the other hand, the hydrodynamic diameter of the BmimPF6-in-water microemulsion was accurately obtained. An unusual phenomenon was demonstrated that Z-average size of BmimPF6-in-water microemulsions decreases with increasing BmimPF6 (oil) concentration at fixed (F127 + n-propanol) concentration.