Ternary cubic phases containing ionic liquid.

The phase diagram of 1-butyl-3-methylimidazolium tetrafluoroborate (bmim-BF(4)) in aqueous solutions of oleyl polyoxyethylene (20) ether (C(18:1)E(20)) was determined at 25 degrees C by a combination of visual inspection and small-angle X-ray scattering (SAXS). The micellar cubic Im3m 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(18:1)E(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 alpha and interfacial area of per surfactant a(S). Furthermore, investigations on the representative micellar Im3m cubic phases formed in a relatively hydrophobic ionic liquid bmim-PF(6) with C(18:1)E(20) and water ternary system (P(1)), a C(18:1)E(20)/water binary system (J(1)), and C(18:1)E(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.