Insight into behaviors of internal interactions and thermodynamic properties of binary mixtures composed of ether-functionalized ionic liquids and 1,4-butyrolactone or propylene carbonate.

• The V E and Δ η values of all mixtures exhibit negative deviation over the mole fraction range. • Based on VFT equation and Arrhenius empirical equation, there is a high correlation σ and T. • [MOEMPYrr]+ acts as HBD and [TFSI]- (or solvent) acts as HBA using the COSMO-RS model. • The interaction between anions and cations in the ILs + PC is stronger than in the ILs + GBL. • In terms of Einstein's equation, D GBL or D PC > D + [MOEMPYrr] > D - [TFSI]. A deeper comprehension of the mechanism behind various internal interactions and their influence on system properties encourages the utilization of ionic liquid mixture systems. In this work, the excess molar volume, viscosity deviation, change of electrical conductivity, and ionicity of both binary mixtures for N-methyl-N-methoxyethylpyrrolidinium bis(trifluoromethanesulfonyl)imide ([MOEMPYrr][TFSI]) ether-functionalized ionic liquids (ILs) with 1,4-butyrolactone (GBL) or propylene carbonate (PC) were systematically studied. The specific interactions between ILs and solvent molecules were investigated by using the COSMO-RS model in terms of DFT calculation. The results indicate that [MOEMPYrr]+ tends to act as a hydrogen bond donor and [TFSI]- tends to act as a hydrogen bond acceptor, and GBL (or PC) has a strong hydrogen bond acceptance ability. Furthermore, based on the radial distribution functions (RDFs) from molecular dynamics (MD) simulations, the H 1 atom in [MOEMPYrr]+, the O 2 atom in [TFSI]-, the O 3 atom in GBL, and the O 4 atom in PC are selected as reference sites to study the interaction between cations and anions (or solvent molecules). It is found that the interaction between anions and cations in the [MOEMPYrr][TFSI] + PC system is stronger than that in the [MOEMPYrr][TFSI] + GBL system, and the interaction between cations and GBL is stronger than that between cations and PC. This result further explains why the excess molar volumes (V E) of [MOMPYrr][TFSI] + GBL binary mixtures are greater than that of [MOMPYrr][TFSI] + PC binary mixtures from a microscopic perspective. [ABSTRACT FROM AUTHOR]