Abstract
Thermal behaviour of five (1-butyl-3-methylimidazolium hexafluorophosphate + multi-walled carbon nanotubes) materials was studied by adiabatic calorimetry over the temperature range (78–370) K. The samples differed by the nanophase content (0.11–0.92 mass fraction), preparative procedure, and appearance ranging from fluids to powders at room temperature. The specific heat capacity of the fluids was found to be an additive quantity of the heat capacities of the components for all phases, and the temperatures of phase transitions did not change relative to the bulk values for the ionic liquid. Evacuation of the contacting components was found to be a necessary step to reproducibly obtain the high-density fluids. However, no notable effect of the evacuation on thermal behaviour of the studied systems was detected. For the powder-like sample with the highest nanophase content, a sigmoidal heat capacity curve was observed. Based on this it was concluded that the internal diameter of the studied nanotubes was small enough to reveal a gradual transition from the crystal-like structures to the liquid-like ones instead of isothermal melting of the ionic liquid.
Highlights
This work continues our activities on thermodynamic characterization of ionic liquid (IL) materials with multiwalled carbon nanotubes (MWCNT) [1]
Based on room-temperature densities measured in this research for ionic nanofluids (INFs) with four ionic liquids (ILs), we conclude that evacuation is a necessary step to maximize the IL penetration into multiwalled carbon nanotubes (MWCNT)
MWCNT and the IL were degassed and, mixed and ground in an agate mortar for 45 min. This technique resulted in low-density INFs, presumably because a significant part of the inner space of the MWCNT was not filled with IL [1]
Summary
This work continues our activities on thermodynamic characterization of ionic liquid (IL) materials with multiwalled carbon nanotubes (MWCNT) [1]. It was noted that such measurements need to be performed using methods with small uncertainty (
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