Experimental and DFT studies on aggregation behavior of dodecylsulfonate-based surface active ionic liquids in water and ethylammonium nitrate

The present work aims to systematically study the aggregation behavior of one halogen-free surface active ionic liquid (SAIL), i.e., 1-butyl-3-methylimidazolum dodecylsulfonate ([C 4 mim][C 12 H 25 SO 3 ]), in water and ethylammonium nitrate (EAN), respectively. Multiple-state ordered aggregates, viz. lyotropic liquid crystals (LLCs) (normal hexagonal and laminar lyotropic liquid phases, i.e. H 1 and L α phases) and lamellar gels, were facilely tuned only by the concentration of SAIL or solvent type. Furthermore, it is particularly interesting that LLC phases were constructed in H 2 O while lamellar gels were obtained in the EAN media environment, which were characterized by polarized optical microscopy (POM) and small-angle X-ray scattering (SAXS). According to the investigative SAXS patterns, some structural parameters were calculated, suggesting that a higher concentration of SAIL results in a denser arrangement whereas an opposite trend generates because of a higher temperature. FT-IR spectra and density functional theory (DFT) calculations reveal that both strong H-bonding and electrostatic interactions between EAN and the headgroups of [C 4 mim][C 12 H 25 SO 3 ] facilitate gelation . For the self-assembled lamellar gels formed by [C 4 mim][C 12 H 25 SO 3 ] in EAN, a thermally reversible sol–gel transition was observed by differential scanning calorimetry (DSC). The rheological results show that the H 1 phase formed by [C 4 mim][C 12 H 25 SO 3 ] in water exhibits a viscoelastic gel-like behavior among the whole frequency region while L α phase displays a viscous behavior at lower frequencies and an elastic behavior at higher frequencies. This work is expected to set a basis for application of the eco-friendly halogen-free SAIL in some fields, e.g. electrochemistry , supramolecular chemistry and drug delivery.