Lyotropic liquid crystalline phases formed in ternary mixtures of N-alkyl-N-methylpyrrolidinium bromide/1-decanol/water

Abstract

The phase behavior of ternary systems involving long-chain pyrrolidinium ionic liquids, N-alkyl-N-methylpyrrolidinium bromide (CnMPB, n = 12, 14, 16), water, and 1-decanol was investigated at 25 °C. Polarized optical microscopy (POM), small-angle X-ray scattering (SAXS), and rheological measurements were employed to investigate the lyotropic liquid crystalline (LC) phases. Lamellar phase (Lα) and hexagonal phase (H1) were found to exist in all the three systems, but the isotropic cubic phase only appears in the C12MPB and C14MPB systems. Greater surfactant content leads to a denser aggregation of the cylindrical units in the H1 phase, and the structural parameters of Lα phase depends on water content. The alkyl chain length of CnMPB also has interesting effect on the structural parameters and rheological properties of the LC phase. Compared with a similar ternary system of 1-hexadecyl-3-methylimidazolium chloride ([C16mim]Cl) and traditional cationic surfactants cetyltrimethylammonium bromide (C16TAB), the effect of the cationic group on the phase behavior was also investigated.