Structure Of The Liquid-vapor Interface Of The Solution Of Ionic Liquid [Emim][Dmp] With Water:a Molecular Dynamic Study

Absorption heat pump and absorption refrigeration cycle can be drived by the low-bit industrial waste heat and have the economic and environmental benefits significant advantages which attracts more and more attention of people around the world. In the absorption cycle, the processes that the resolution of the absorbent and the absorption of refrigerant are the key to achieving the application of cooling or heating. However, the common working pairs of the absorption cycle exist much defects, such as toxicity (NH3/H2O), corrosion and easy crystallization (LiBr/H2O).Ionic liquids are a new type of green solvent developed under the concept of green chemistry and own many characteristics, such as low volatility, wide solution process, good chemical, thermal stability and having adjustability. Therefore, ionic liquids have been the research hotspot in various fields. In recent years, many scholars have proposed that the ionic liquids could be used as the absorbent of the working pairs.Molecular dynamics simulation is an effective tool to analyze the relationship between microstructure and macroscopic natures of the ionic liquids. In this paper, we studied the aqueous solution of ionic liquid ([Emim][Dmp]) and its interfacial microstructure properities by molecular dynamics simulation. The main research work are summarized as follows:First, we used the molecular dynamics simulation software DL_POLY to simulate the thermodynamic properities, kinetic properties and microstructure of the aqueous solution of ionic liquid ([Emim][Dmp]) at different temperatures and different concentrations, such as: density, thermal expansion coefficient, diffusion coefficient, viscosity and radial distribution function. The simulated results are in good agreement with the experimental values which indicating that the selected and polarized force field in this paper could describe the system well.Second, the gas-liquid interface models between ionic liquid and its aqueous solutions were builded. Molecular dynamics simulations were performed to study the influences of temperature and concentration on the interfacial density distribution, thickness, surface tension and analyze the distribution information of direction of the cation ([Emim]) at the interface. As the temperature rised, the liquid densities decreased, the thicknesses of the interface increased, the surface tensions reduced. As the number of water molecules in the ionic liquid content increased, the densities and surface tensions of the liquid phase decreased gradually, the interface thicknesses had an trend of increasing after lower first. The imidazole ring of the cation tended to perpendicular to the interface with its ethyl chain pointed to the vapor and methyl chain pointed to the liquid phase. The atom oxygen (O1) of the anion and the atom carbon attached to the oxygen pointed to the gas phase.Finally, we used the molecular dynamics simulation software LAMMPS to study the dynamic process of the absorption of water vapor by the aqueous solution of ionic liquid and lithium bromide under nonequilibrium conditions. At473.15K and the same molar concentration (0.4), the two working pairs perfromed the same capability in absorbing the number of water molecules.