Abstract: The self-assembly of surface active ionic liquid 1-(2-hydroxyethyl)-3-dodecylimidazolium chloride（[C2OHC12im]Cl） in aqueous solutions with various inorganic salts (NaX, X=Cl-, Br-and I-, Na2SO4) has been investigated by surface tension method and fluorescence probe method, respectively. The critical micelle concentration(CMC) and average aggregation number(Nm) of [C2OHC12im]Cl changed remarkably in aqueous medium with the presence of counter ions. It is believed that the [C2OHC12im]+ monomers or micelles are combined with the counter ions to neutralize their surface charges. The order of the counter ions in altering the selfassembly parameters of [C2OHC12im]Cl in aqueous medium follows Cl-＜Br-＜I-＜SO2-4. However, the effects of the category of counter ions on the critical aggregation number(Nm,C) and the micropolarity of micelle([I1/I3]m) were marginal. Along with the increase of the concentration of Br-, the CMC decreases logarithmically and the Nm increases by an empirical power law.

Key words: surface active ionic liquid, (hydroxylthyl)dodecylimidazolium chloride, inorganic counter ion, self-assembly