Ternary cubic phases containing ionic liquid

Abstract

The phase diagram of 1-butyl-3-methylimidazolium tetrafluoroborate (bmim-BF 4) in aqueous solutions of oleyl polyoxyethylene (20) ether (C 18:1E 20) was determined at 25 °C by a combination of visual inspection and small-angle X-ray scattering (SAXS). The micellar cubic I m 3 m liquid crystalline phase found in the ternary system was investigated by means of SAXS and rheological techniques. The cubic samples show highly elastic gel-like properties indicated by their mechanical and discrete relaxation spectra. Moreover at a constant C 18:1E 20/bmim-BF 4 ratio, with decreasing water content the network strength increases. The internal structure apparently becomes more stable, as indicated by an increase in the storage and loss moduli and a decrease in the lattice parameter α and interfacial area of per surfactant a S . Furthermore, investigations on the representative micellar I m 3 m cubic phases formed in a relatively hydrophobic ionic liquid bmim-PF 6 with C 18:1E 20 and water ternary system (P 1), a C 18:1E 20/water binary system (J 1), and C 18:1E 20/water/bmim-BF 4 system (B 1) were made in comparison. It can be clearly seen that appreciably different mechanical spectra and relaxation spectra are shown by the cubic phases investigated. B 1 exhibits a typical gel-like dynamic rheogram while P 1 exhibits fluid-like viscoelastic properties to some extent, and J 1 shows traits of the general Maxwell model. These differences are analyzed through SAXS data as the employment of ionic liquids and their different location in the cubic phases.