Nonaqueous Lyotropic Liquid-Crystalline\nPhases Formed\nby Gemini Surfactants in a Protic Ionic Liquid

Abstract

The aggregation behaviors of three Gemini surfactants\n[(C_<i>s</i>H_2<i>s</i>-α,ω-(Me₂N⁺C_<i>m</i>H_2<i>m</i>+1Br^–)₂, <i>s</i> = 2, <i>m</i> = 10, 12, 14] in a protic ionic liquid,\nethylammonium nitrate (EAN), have been investigated. The polarized\noptical microscopy and small-angle X-ray scattering (SAXS) measurements\nare used to explore the lyotropic liquid crystal (LLC) formation.\nCompared to the LLCs formed in aqueous environment, the normal hexagonal\nand lamellar phases disappear. However, with increasing the surfactant\nconcentration, a new reverse hexagonal phase (H_II) can\nbe mapped over a large temperature range except for other ordered\naggregates including the isotropic solution phase and a two-phase\ncoexistence region. The structural parameters of the H_II are calculated from the corresponding SAXS patterns, showing the\ninfluence of surfactant amount, alkyl chain length, and temperature.\nMeanwhile, the rheological profiles indicate a typical Maxwell behavior\nof the LLC phases formed in EAN.