Origin of low melting point of ionic liquids: dominant role of entropy |
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| Authors: | Takatsugu Endo Kouki Sunada Hiroki Sumida Yoshifumi Kimura |
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| Affiliation: | Department of Molecular Chemistry and Biochemistry, Faculty of Science and Engineering, Doshisha University, 1-3 Tatara Miyakodani, Kyotanabe Kyoto 610-0394 Japan.; Department of Applied Chemistry, Graduate School of Science and Engineering, Doshisha University, 1-3 Tatara Miyakodani, Kyotanabe Kyoto 610-0394 Japan |
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| Abstract: | Ionic liquids (ILs) are salts with an extremely low melting point. Substantial efforts have been made to address their low melting point from the enthalpic standpoint (i.e. interionic interactions). However, this question is still open. In this study, we report our findings that entropic (large fusion entropy), rather than enthalpic, contributions are primarily responsible for lowering the melting point in many cases, based on a large thermodynamic dataset. We have established a computational protocol using molecular dynamics simulations to decompose fusion entropy into kinetic (translational, rotational, and intramolecular vibrational) and structural (conformational and configurational) terms and successfully applied this approach for two representatives of ILs and NaCl. It is revealed that large structural contribution, particularly configurational entropy in the liquid state, plays a deterministic role in the large fusion entropy and consequently the low melting point of the ILs.Large structural entropy makes salts liquid at room temperature. |
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