Effect of L64 on the Phase Behavior of 1-Dodecyl-3-methylimidazolium Chloride/Water System

Phase behavior of ternary system involving surfactant-like ionic liquid 1-dodecyl-3-methylimidazolium chloride ([C(12)mim]Cl), water, and nonionic surfactant PEO-PPO-PEO block copolymer (Pluronic L64) is investigated at 25 degrees C. Hexagonal (H(1)) and lamellar liquid crystal phase (L alpha) are found in [C(12)mim]Cl/H(2)O/L64 system by using polarized optical microscopy (POM), small-angle X-ray scattering (SAXS) techniques and (2)H NMR spectra. The phase structure (H(1) phase), which is formed in [C(12)mim]Cl/H(2)O binary system, is not changed when L64 with a low concentration is added. However, phase transitions will occur from hexagonal to multiphases of H(1) and cubic phases (C), then to L alpha+C phases with constant [C(12)mim]Cl/H(2)O ratio and increasing L64 concentration. Moreover, at given L64 (5%, 20%) concentration, the lattice parameter of H(1) or L alpha phase decreases with increasing [C(12)mim]Cl/H(2)O ratio. Fourier transform infrared (FTIR) spectra indicate that the H-bonded network comprising an imidazolium ring, chloride ion and water formed in [C(12)mim]Cl/H(2)O binary system is disrupted upon addition of L64. This is helpful to the phase transition, due to the decreasing of interfacial curvature induced by dehydration of hydrated layer after the addition of PEO block of L64.