Melting Behavior of Pyrrolidinium-Based Ionic Liquids and Their Binary Mixtures

To understand the low-temperature behavior of pyrrolidinium-based ionic liquids (ILs), ILs, including N-butyl-N-methyl pyrrolidinium (Pyr(14)(+)) and N-methyl-N-propyl pyrrolidinium (Pyr(13)(+)) cations and bis(fluorosulfonyl)imide (FSI-), bis(trifluoromethanesullonyl)imide (TFSI-), bis(pentalluoroethanesulfonyl)imide (BETI-), and (trifluoromethanesullonyl)(nonafluorobutyl-sulfonyl) imide (IM14-) anions, were investigated. Pyr(14)FSI, Pyr(13)FSI, Pyr(14)TFSI, Pyr(13)TFSI, Pyr(14)BETI, Pyr(13)BETI, Pyr(14)IM(14), and Pyr(13)IM(14) were prepared and intensively studied by means of differential scanning calorimetry (DSC). Four of these ILs (Pyr(14)FSI, Pyr(13)FSI, Pyr(14)TFSI, Pyr(13)TFSI) were used to prepare binary mixtures, which were examined by DSC measurements. For these mixtures, reduced melting transitions and an enhanced liquidus range were detected, which represents a great advantage for low-temperature applications. In addition, it was observed that the crystallization process of the mixtures is mainly influenced by the anion.