Ternary cubic phases containing ionic liquid

The phase diagram of 1-butyl-3-methylimidazolium tetrafluoroborate (bmim-BF4) in aqueous solutions of oleyl polyoxyethylene (20) ether (C18:1E20) was determined at 25 °C by a combination of visual inspection and small-angle X-ray scattering (SAXS). The micellar cubic Im3mIm3m 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 C18:1E20/bmim-BF4 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 aSaS. Furthermore, investigations on the representative micellar Im3mIm3m cubic phases formed in a relatively hydrophobic ionic liquid bmim-PF6 with C18:1E20 and water ternary system (P1), a C18:1E20/water binary system (J1), and C18:1E20/water/bmim-BF4 system (B1) were made in comparison. It can be clearly seen that appreciably different mechanical spectra and relaxation spectra are shown by the cubic phases investigated. B1 exhibits a typical gel-like dynamic rheogram while P1 exhibits fluid-like viscoelastic properties to some extent, and J1 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.

Graphical abstractDiscrete relaxation spectra of the cubic liquid crystals at 25 °C for C18:1E20/water/bmim-BF4 (B1, B2, B3), C18:1E20/water/bmim-PF6 (P1), and C18:1E20/water (J1) systems.Figure optionsDownload full-size imageDownload as PowerPoint slide