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چکیده
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We studied the liquid structures of a series of dual-functionalized ionic liquids (DFILs). These DFILs consist of functionalized imidazolium cations with a nitrile group and varying lengths of ether side chains, paired with bis(trifluoromethyl sulfonyl) imide anions, denoted as [C2CNIm(EtO)nMe][Tf2N]. Our study employed molecular dynamics (MD) simulation, utilizing the all-atom OPLS (OPLS-AA) force field to model the interaction between atoms. We employed several analysis techniques, including distribution functions, Voronoi tessellation, and cluster analysis, to probe the liquid structures. Furthermore, we explored dynamic properties such as mean-square displacements (MSD), self-diffusivity coefficients, hydrogen bonding, ion pairing, and ion cage effects. The current study aims to shed light on the effect of cationic ether chain length on the structural and dynamic behavior of the DFILs. The validity of our simulation method and force field was examined by reproducing experimental density data. Our findings revealed a correlation between the length of the ether side chains and the density of the studied DFILs when the longer side chains lead to a decreased density. Calculated partial radial distribution functions (PRDF) of ether side chains of the cations demonstrated a tendency for self-aggregation as the chain length increased. The PRDF analysis showed that the acidic hydrogen atoms of the imidazolium ring of the cations prefer the nitrogen and oxygen atoms of the anions for hydrogen bonding. The hydrogen bond between anions and cations is more pronounced for cations with smaller side chains, as shown in the combined distribution functions (CDF) diagrams. Anions displayed higher diffusivity than the cations, and among the cations, [C2CNIm(EtO)6Me]+ has the lowest diffusion coefficient. We evaluated structural heterogeneity using structure factors, heterogeneity order parameters (HOP), and domain analysis based on Voronoi tessellation. Finally, we delved into dynamical heterogeneity, investigating hydrogen bond stability, ion pairing, ion cage effect, reorientation dynamics, and cluster analysis of ions. The micro-heterogeneity of DFILs is significantly impacted by the ether side chain, as indicated by the results. Specifically, [C2CNIm(EtO)6Me][Tf2N] with a longer ether side chain exhibits more significant microstructural heterogeneity compared to other studied DFILs. Moreover, the difference in the stability of ion pairs among the studied DFILs is more pronounced than in the ion cage
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