Influence of PEG-containing cation on molecular state of water in water – Acetate based ionic liquids mixtures

Abstract

Two acetate ionic liquids (ILs) based on N-methyl-pyrrolidinium cation with etheric (mPEGn-) and aliphatic (butyl-) substitutions were synthetized. Electrochemical potential windows (EPWs) were measured on a glassy carbon electrode. The results revealed that introduction of etheric group in the IL structure constricts the EPW if compared with aliphatic substitution. The binary mixtures of ILs with water were characterized by Raman, Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopies and Molecular Dynamics (MD) simulations. Intermolecular hydrogen bonds between acetate anions and ether-substituted cations have been found. Detailed analysis of local structure of water in these mixtures by ATR-FTIR and MD simulations indicates that “free water phase” clusters appear when the molar ratio between water and IL, n(H2O)/n(IL), is larger than 3 in case of [BMPyr]AcO and larger than 7 for [mPEGnMPyr]AcO. The evolution of the specific conductivity of water-ILs mixtures with water content well correlates with the modification of the water state.