A simulation study of microstructure and dynamics of Dual-functionalized imidazolium based Ionic Liquids (DFILs)

Abstract The liquid structures of a series of dual-functionalized ionic liquids (DFILs) composed of functionalized imidazolium cations containing a nitrile group and varying ether side-chain length and bis(trifluoromethylsulfonyl)imide, [Tf2N]− anions were studied using molecular dynamic simulation. The interactions between species were described by all-atom OPLS force field. Liquid structures and ionic dynamics were explored. The aim of the current study is to shed light on the effect of cationic ether chain length on the structure and dynamic properties of [C2CNIm (EtO)6 Me]+ DFILs. The accuracy of the applied simulation method and FF were justified by reproducing the experimental densities. Results of this study demonstrated that densities of the studied DFILs decreased by increasing of ether side-chain length. Partial radial distribution functions (PRDFs) showed that despite the larger number and less hindered fluorine atoms than other atoms of anions, the side H atoms of the imidazolium ring of cations tend to spend more time around the nitrogen and oxygen atoms of the anions. Calculated PRDFs for the center of mass of cationic ether chains indicated that in the case of [C2CNIm (EtO)6 Me]+ cation, the self-aggregation of ether chains occurs by lengthening the chain. Combined distribution functions show that the strength of hydrogen bonding increase by decreasing ether side-chain length. Calculated diffusion coefficients demonstrate that anion has higher diffusivity than cations. In the case of [C2CNIm (EtO)6 Me]+, the diffusion coefficient is smaller due to its longer ether chain, which can restrict its mobility.