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Thermal Behaviors and Ion Structures of Ionic Liquids

Melting points of ordinary inorganic salts are high compared to molecular liquids due to strong coulombic interaction, e.g. the melting point of NaCl is ca 801oC. However, the melting points of the salts called ionic liquids (ILs) are at or near room temperature. Then ILs have been attracted much attention as a new class of liquids.

Our research group is focusing on unique thermal properties of ILs, such as low melting point, premelting over a wide temperature range, excessive supercooling, tendency toward glass formation from the liquid state upon cooling, and extreme thermal history. This research is collaborated with Prof. K. Tozaki at Faculty of Education of Chiba University.

We observe thermal behaviors of ILs by lab-made calorimetries with high sensitivity and temperature stability. The characteristic of these apparatuses is the use of thermoelectric modules as heat flow sensors and heat pumps. Simultaneous measurements of Raman spectroscopy/calorimetry and quantum chemical calculations are carried out to discuss the thermal behaviors at the molecular level.

K. Nishikawa, S. Wang and K. Tozaki, Chem. Phys. Lett., 2008, 458, 88-91
T. Endo, T. Kato, K. Tozaki, and K. Nishikawa, J. Phys. Chem. B, 2010, 114, 407-411

Fig.1 DSC trace of [C4mim]Br. Large fluctuation of heat flow was observed during melting. (region (3), see inset)

Fig.2 Heat flow curve of [C4mim]PF6. Three crystalline phases were observed, and the difference in each phase was seen in the conformation of the butyl group.

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