Phase Behavior of Liquid Crystals Formed in [C12mim]CI/H2O and [C12mim]CI/Alcohols Systems

• Published in: Chinese journal of chemical physics Vol. 22; no. 5; pp. 453 - 459
• Main Authors: Pei, Mei-shan, Wu, Zhi-yan, Wang, Lu-yan, Wu, Xin-zhou, Tao, Xu-tang
• Format: Journal Article
• Language: English
• Published: IOP Publishing 01.10.2009
• Subjects: Differential scanning calorimetry; Lyotropic liquid crystal; 1-dodecyl-3-methylimidazolium chloride; Small-angle X-ray scattering
• ISSN: 1674-0068; 2327-2244
• DOI: 10.1088/1674-0068/22/05/453-459

Phase behaviors of different binary systems involving 1-dodecyl-3-methylimidazolium chloride ([C12mim]Cl) and H2O, [C12mim]Cl 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 [C12mim]Cl/H2O system, and lamellar liquid-crystalline (L) phase is found in [C12mim]Cl/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 [C12mim]Cl/1-octanol system, the lattice spacings of lamellar phase increase with increasing C12mimCl concentration, which is opposite to the results of [C12mim]Cl/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 differential scanning calorimetry indicate that the lamellar phase is stable within a wide temperature range above room temperature. However, the lattice spacings decrease with the increase of temperature, which may be due to the softening of the hydrocarbon chain of [C12mim]Cl molecules. In different alcohols systems, it is found that the lamellar lyotropic liquid crystal structure is easier to be formed when the carbon chain length becomes longer.