Phase Behavior of Liquid Crystals Formed in C₁₂mimCl/H₂O and C₁₂mimCl/Alcohols Systems

Phase behaviors of different binary systems involving 1-dodecyl-3-methylimidazolium chlo-ride (C₁₂mimCl) and H₂O, C₁₂mimCl and different alcohols (1-butanol, 1-pentanol, 1-hexanol and 1-octanol) are investigated at 25 °C. Hexagonal liquid crystal phase (H₁) is identified in C₁₂mimCl/H₂O system, and lamellar liquid-crystalline (L_α) phase is found in C12mimCl/alcohols systems by using polarized optical microscopy and small-angle X-ray scattering techniques. The formation of such phases is considered as a synergetic result of the solvatophobic force and the hydrogen-bonded network comprising an imidazolium ring,chloride ion and water (or alcohols), which can be confirmed by Fourier transform infrared spectra. It is noticeable that in C₁₂mimCl/1-octanol system, the lattice spacings of lamel-lar phase increase with increasing C₁₂mimCl concentration, which is opposite to the results of C₁₂mimCl/H₂O system. This may result mainly from stronger static repulsion among hydrophilic headgroups of imidazolium salts arranged in the bilayers of lamellar structures.Further measurements by diffrential scanning calorimetry indicate that the lamellar phase is stable within a wide temperature range above room temperature. However, the latticespacings decrease with the increase of temperature, which may be due to the softening of the hydrocarbon chain of C₁₂mimCl molecules. In different alcohols systems, it is foundthat the lamellar lyotropic liquid crystal structure is easier to be formed when the carbon chain length becomes longer.