Molecular simulations of phosphonium-based ionic liquid

Compared with imidazolium-based ionic liquids (ILs), phosphonium-based ILs have been proven to be more stable in thermodynamics and less expensive to manufacture. In this work, a kind of phosphonium-based IL, [PC₆C₆C₆C₁₄][Tf₂N], was studied under several conditions using molecular dynamics simulations based on both the all-atom force field (AAFF) and the united-atom force field. Liquid density was calculated to validate the force field. Compared with experimental data, good agreement was obtained for the simulated density based on the AAFF. Heat capacities at constant pressure were calculated at several temperatures, and good linear relationships were observed. Self-diffusion coefficients, viscosities and conductivities were also calculated to study the dynamics properties of this IL. The viscosity of this IL at 293 K was also compared with experimental data, and the error was in a reasonable range. In order to depict the microstructures of the IL, centre-of-mass and site-to-site radial distribution functions were employed. In addition, spatial distribution functions were investigated to present the more intuitive features.