Halide Ions Effects on Surface Excess of Long Chain Ionic Liquids Water Solutions

초록

The interfacial structure and composition of water solutions with alkylimidazolium ionic liquids varying in their halide anions ([C(12)mim][X], X = Cl and I) were investigated by X-ray near-total-reflection fluorescence spectroscopy and X-ray reflectivity measurements. We demonstrate that X-ray fluorescence and reflectivity techniques provide a more direct measurement of surface adsorption. Furthermore, we show that for [C(12)mim][Cl] and [C(12)mim][I] solutions with mixed inorganic salts (NaI, NaCl), I- ions replace Cl- above the critical micelle concentration (CMC) of [C(12)mim][Cl] at much lower concentrations of NaI whereas NaCl concentrations a hundred times higher than the CMC of [C(12)mim][I] only partially replace the I- at the interface. Our surface-sensitive X-ray diffraction and spectroscopy provide two independent tools to directly determine the surface adsorption of ionic surfactants and the interfacial composition of the surface films.

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