Effect of increasing the cation chain length on thermodynamic and transport properties of ionic liquids using molecular dynamics

In this study, Molecular Dynamics (MD) simulations are employed to observe the effect of different chain lengths on density, self-diffusion coefficient and viscosity of [Cnmim][TF2N] ionic liquids (ILs). Both density and self-diffusion coefficient decrease as the chain length increases. The rheological curves show a shear-thinning after Newtonian behavior. The results suggest that viscous thinning is related to the decrease in the number of hydrogen bonds (H-bonds) and the alignment of the alkyl chains in the flow direction. Viscosity values at zero-shear-rate increase as the chain size does. Moreover, the static structure factor indicates anisotropy in systems with cation alkyl chains of 6 and 8 carbon atoms. However, in a 10 carbon atom cation alkyl chain, a more ordering is observed.