Melting and freezing behaviors of prototype ionic liquids, 1-butyl-3-methylimidazolium bromide and its chloride, studied by using a nano-Watt differential scanning calorimeter.
1-Butyl-3-methylimidazolium bromide ([bmim]Br) and its chloride ([bmim]Cl) are representative prototypes of ionic liquids. We investigated the melting and freezing behaviors of [bmim]Br and [bmim]Cl by using a homemade differential scanning calorimeter (DSC) with nano-Watt stability and sensitivity. The measurements were carried out at heating and cooling rates slow enough to mimic quasi-static processes. Their thermal behaviors of melting and freezing show characteristic features such as a wide pre-melting range and excessive supercooling and individual behaviors of single crystals even for the same substance. The melting temperatures of [bmim]Br and [bmim]Cl were determined from the broad DSC traces and discussed in relation to the crystal structure. We suggest that the observed characteristics are due to the dynamics of the cooperative change between gauche-trans (GT) and trans-trans (TT) conformations of the butyl group in the [bmim]+ cation.
Nishikawa
Keiko
K
Graduate School of Science and Technology, Chiba University, Yayoi, Chiba, 263-8522, Japan. k.nishikawa@faculty.chiba-u.jp
Wang
Shaolan
S
Katayanagi
Hideki
H
Hayashi
Satoshi
S
Hamaguchi
Hiro-o
HO
Koga
Yoshikata
Y
Tozaki
Ken-ichi
K
D002152:Calorimetry, Differential Scanning / Q000295:instrumentation / Q000379:methods*; D007093:Imidazoles / Q000737:chemistry*; D052578:Ionic Liquids / Q000737:chemistry*; D015394:Molecular Structure; D012680:Sensitivity and Specificity; D013696:Temperature
D007093:Imidazoles; D052578:Ionic Liquids; C502841:1-butyl-3-methylimidazolium chloride