Small-Angle X-ray Scattering Measurements of Ionic Liquids Pressurized with Carbon Dioxide Using Titanium Sample Holder: 1-Butyl-3-methylimidazolium Bis(trifluoromethylsulfonyl) Amide Mixtures up to 22MPa

A high-pressure sample holder made entirely of titanium and a titanium alloy was constructed for small-angle X-ray scattering (SAXS) measurement of ionic liquids pressurized with CO2. It is designed to vary the path length precisely and perform stable operation at high temperature and pressure, while retaining a constant path length. An in situ beam-monitoring detector for the transmitted X-rays was redesigned and used. SAXS experiments were carried out for an imidazolium-based ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) amide, pressurized and saturated with CO2. Zero angle scattering intensities, I(0), which directly relate to the mesoscale structural fluctuation, are evaluated from the obtained SAXS intensities. Values of I(0) meaningfully change with the CO2 solubility. By using the constructed apparatuses, the anomalous behavior of CO2 dissolution into ionic liquids is clarified from the viewpoint of the mesoscale structural change of ionic liquids that fluctuated by dissolved CO2. The present system for SAXS measurement is widely applicable to investigations on structural fluctuations of liquids, solutions including phase separated systems, which are the same as the ionic liquids and CO2 mixtures, and amorphous solids under extreme conditions. (C) 2012 The Japan Society of Applied Physics