We have investigated phase-transition behaviors of a typical room temperature ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([C(4)mim]PF(6)), using calorimetric and Raman spectroscopic techniques. Although there was some confusion on its phase behaviors in previous reports, our measurements with a laboratory-made calorimeter at a slow scanning rate (5 mK/s) have definitely revealed that [C(4)mim]PF(6) has three crystalline phases. From the Raman spectroscopic study, the conformations of the butyl group for these crystalline phases are assigned to gauche-trans, trans-trans, and gauche'-trans conformations in lower-energy order. It has been also shown that these three conformers coexist in the liquid, supercooled liquid, and glass states. It is concluded that all of the phase transitions of [C(4)mim]PF(6) except the glass transition are associated with conformational changes of the butyl group.

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.

The magnetic effect on the melting transition of H2O and D2O was measured by using a high resolution and supersensitive differential scanning calorimeter working in a magnetic bore. The melting temperature of H2O and D2O at 6T was 5.6 and 21.8mK higher than that without the magnetic field, respectively. The temperature shifts of the melting transition of H2O and D2O were proportional to the square of the magnetic field. The temperature shifts of the melting transition due to the magnetic field did not obey the magneto-Clapeyron equation quantitatively. A dynamic effect due to the magnetic field was discussed for an alternative interpretation.

The thermal properties of water confined to both exterior and interior of cylindrical mesoporous MCM-41 (pore diameter d = 1.8-3.6 nm) were analysed by differential scanning calorimetry and FTIR spectroscopy. A three-step freezing of the exterior water was observed just above 233 K, the homogeneous nucleation temperature of bulk water, before the interior water was frozen. The first freezing of water was ascribed to the outermost bulk water, the second one to water between bulk and water bound to the exterior wall, and the third one to the bound exterior water. With decreasing pore size, the second freezing water decreased in magnitude. This stepwise freezing of the exterior water has been found in porous zeolite materials. The exothermic peak of the interior water confined in MCM-41 was observed at 227.5 K before freezing, ascribed probably to a high-density liquid-low-density liquid phase change. FTIR data of the interior water confirmed this finding. The present results substantiate the static and dynamic crossover of supercooled water in MCM-41 reported from previous neutron scattering and NMR data.