Complicated temperature-induced phase transitions were shown in two hexagonal liquid crystal mesophases constructed by nonionic surfactant C 18:1 E 10 in the media of water with ionic liquids, 1-butyl-3-methylimidazolium tetrofluoroborate (bmim-BF 4 ) and 1-butyl-3-methylimidazolium hexafluorophosphate (bmim-PF 6 ), respectively. Detailed phase transition information was extracted from rheological, polarized optical microscopy, deuterium magnetic resonance spectroscopy and smallangle X-ray scattering measurements, with good agreement among these techniques. It is shown that the order-to-disorder phase transition occurred in a narrow range of temperatures for both the two hexagonal mesophases. In particular, the mesophases experienced a biphasic hexagonal-lamellar coexisting before completely melting, which was not found in the corresponding aqueous hexagonal system of the same surfactant concentration. Of most importance, the two target mesophases exhibited some clearly different behaviors. The phase transition temperature is much higher (ca. 10°C) in a (water ? bmim-BF 4 ) system than in a (water ? bmim-PF 6 ) system. After melting, a fast transition from elastic micelle to Newtonian fluid was observed in the (water ? bmim-BF 4 ) system, while the micelle related to the (water ? bmim-PF 6 ) system remained elastic over a relatively wide temperature region. The results obtained give a better insight of how the mixed solvents support mesophase formation and modulate the phase transition.

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