Room Temperature Ionic liquids (RTIL) are salts in a liquid state. Unlike ordinary liquids such as Water or gasoline, which are made of charge-neutral molecules, Ionic liquids are made of Ions. Ionic liquids have applications as green solvents in chemical catalysis, analysis of different chemicals, and manufacturing of solar cells. They have potential applications in liquid heat storage devices and electrochemical capacitors. To engineer devices for these applications it is important to know the thermal transport properties of Ionic liquid. RITLs are dominated by salts derived from 1-methylimidazole, the system I am studying is BMIM-PF6 Ionic liquid. I use Non-equilibrium Molecular dynamics to predict the thermal properties of BMIM-PF6 liquid to prove its potential as a material for liquid thermal storage devices for my master's thesis.
I carried out an extensive literature review of Ionic liquids to find experimental as well as molecular dynamic analysis studies. Currently, ionic liquids are used as green solvents in chemical reactions. However, physicists and engineers are more excited about the application of Ionic liquids as liquid heat storage devices and electrochemical capacitors. Salts like NaCl are thermally stable, so it is expected that Ionic liquids are also thermally stable at high temperatures.Â
Experimentally Ionic liquids are viscous liquids and there are experimental results for the thermal conductivity of many Ionic liquids at room temperatures. Ionic liquids are very expensive and no studies have been carried out at high temperatures. The project aims to contribute high-temperature transport coefficients of Ionic liquids using Molecular dynamic simulations.
I use several Molecular dynamics software packages, Packmol, VMD, LAMMPS and OVITO for modelling and calculating the transport properties of Ionic Liquids. Equilibrium simulations in NVE and NVT ensembles were used to calculate mean square displacement for the Diffusion coefficient of the Ionic liquid, pressure tensors for Green Kubo Autocorrelation functions were used to calculate viscosity values and Non-equilibrium simulations with enhanced Heat exchange algorithm were used to find the thermal conductivity of the liquid. I further use Python scripts to find the values of Diffusion, Viscosity and thermal conductivity. The figure on the top left shows the calculated values of Viscosity autocorrelation functions and the bottom figure depicts the calculated MSD.
I studied the Ionic liquid system at different temperatures to see the temperature dependence of the transport properties. I took the system temperature down to 100K to find properties of solid Ionic salts, I moved it to higher temperatures of 400K, 500K and 600K to test the thermal stability of the Ionic liquid. Liquid energy storage devices have very high operating temperatures, so it is important to understand the temperature-dependent thermal conductivity of the Ionic liquids at high temperatures to know the performance of the devices.