Characterization of lamellar phases fabricated from Brij-30/water/1-butyl-3-methylimidazolium salts ternary systems by small-angle X-ray scattering

The lamellar liquid crystalline phases composed of either imidazolium salt, the hydrophilic 1-butyl-3-methylimidazolium tetrafluoroborate (bmim-BF4) or the hydrophobic 1-butyl-3-methylimidazolium hexafluorophosphate (bmim-PF6), in aqueous solution of Brij-30 (tetraethylene glycol lauryl ether, C12E4) have been assembled at a constant temperature (T = 25 °C). Their elaborate structures such as the distribution of hydrophobic or hydrophilic parts of surfactant bilayer and water are revealed quantitatively by several structural parameters derived from small-angle X-ray scattering (SAXS) measurements. The effects of system composition and temperature on the lamellae are discussed with comparison to the corresponding Brij-30/water binary mixture. It concludes that the bmim-PF6 molecules tend to situate at the interface between polar and apolar regions and therefore cause a decrease of combined water amount around EO blocks. Bmim-BF4 molecules, however, like to locate themselves at water interlayers as well as in the polar domains. In addition, the pseudo-hexagonal columnar structures or micelles observed respectively at low or high temperatures are analyzed by SAXS and differential scanning calorimetry (DSC) methods.