Binary Mixtures of Ionic Liquids to Enhance Dicationic Ionic Liquid Performance: Insights from Molecular Dynamics Simulations and Quantum Mechanics

In this work, the effect of adding a monocationic ionic liquid (MIL) on the properties of a dicationic ionic liquid (DIL) was investigated using molecular dynamics (MD) simulations and quantum mechanical (QM) calculations. The binary mixture of [C₆(mim)₂][NTf₂]₂ (DIL) and [P₁EOE][NTf₂] (MIL) was analyzed in terms of thermophysical, structural, and dynamical properties, along with density functional theory (DFT) and atoms-in-molecules (AIM) analyses. These properties were compared to those of the pure DIL system. Structural properties were examined using radial distribution functions (RDFs) and hydrogen-bonding networks, providing insights into ion arrangement, spatial heterogeneity, and interaction strength. RDF analysis revealed that increasing the MIL mole fraction enhances the local density of anions near the ring hydrogen atoms more significantly than the bulk density. Furthermore, the orientation of imidazolium rings suggests that MIL promotes π-π stacking interactions among [C₆(mim)₂]²⁺ cations. Notably, the system with <i>x</i>_MIL = 0.50 exhibited the lowest structural heterogeneity among the investigated mixtures. Dynamical properties, including mean square displacement (MSD), ionic conductivity, and van Hove correlation functions, were also analyzed. The results indicate that adding MIL enhances microheterogeneity and reduces ion cage strength, thereby facilitating ion mobility and increasing ionic conductivity. QM calculations further demonstrate that adding MIL lowers ion interaction energies due to the formation of stronger hydrogen bonds in the mixture. Additionally, AIM analysis reveals that the presence of MIL increases electron density between the dication and anions.