The unique properties of ionic liquids make them promising for a variety of applications from electrochemistry and “green” solvents [1] to heat transfer fluids or energy storage media in solar thermal systems [2]. Stresses during the liquid to solid phase transitions for crystal-forming fluids with graphite nanoparticles led to large shifts in thermal and electrical conductivities [3]. The large number of possible cation-anion combinations for ionic liquids yields a large range of properties and allow selection of the material melting point, crystal structure, thermal conductivity, and electrical conductivity. In this work, graphite nanoparticles are suspended in crystal-forming ionic liquids (including 1-butyl-3-methylimidazolium chloride, [bmim][Cl]) to exploit these phase-change stresses and produce large contrast between the liquid and solid properties. Thermal conductivity and thermal diffusivity are measured using the transient hot wire and laser flash techniques, while electrical impedance spectroscopy characterizes the electrical properties. Differential scanning calorimetry measures the heat capacity and phase change properties of the ionic nanofluids. Independent characterization of these properties in the liquid and solid state provides insight into the fundamental charge and heat transport mechanisms within the material.

References:

1. Tsuda, T. and C.L. Hussey, Electrochemical Applications of Room-Temperature Ionic Liquids. Electrochemical Society Interface, 2007. 16(1): p. 42-49.

2. Van Valkenburg, M.E., et al., Thermochemistry of ionic liquid heat-transfer fluids. Thermochimica Acta, 2005. 425(1–2): p. 181-188. 3. Zheng, R., et al., Reversible temperature regulation of electrical and thermal conductivity using liquid–solid phase transitions. Nature Communications, 2011. 2: p. 289.