Exploring solvation behaviour of biocompatible ionic liquid 2-hydroxyethylammonium formate + polyethylene glycols mixtures: Role of oxyethylene and hydroxyl units of PEGs

Abstract

The favourable modification of the physicochemical properties of the ionic liquid with green co-solvent and their molecular level characterization with spectroscopic techniques is the area of current research. Further, the co-solvent modified ionic liquid mixtures furnishes interesting properties which render the utility of these solvents in several important applications. In the current work, the effects of addition of two polyethylene glycols (PEGs) with average molecular weights of 200, and 600 on solvent properties of IL 2-hydroxyethyl ammonium formate (HEF) has been explored with the help of solvatochromic absorbance probes. The physicochemical characteristics of the ionic liquid mixtures are altered in an unexpectedly positive way when PEGs are added to IL HEF. The absorbance behaviour of the solvatochromic probes Reichardt dye 33 shows interestingly positive non-ideal behaviour, which may be attributed to the high dipolarity/polarizability (π*) and hydrogen bond donor ability (HBD) (α) of the HEF + PEG mixtures. Further, the Kamlet-Taft parameters, including hydrogen bond acceptor ability (HBA) (β), and hydrogen bond donor ability (HBD) (α), and dipolarity/polarizability (π*) of the HEF + PEG binary mixtures display nonideality, which may be because of the strong Hydrogen bond networking of HEF-PEG molecules along with solute-HEF/PEG interaction present in the mixtures. Moreover, the preferential solvation approach has been invoked to explore the solute–solvent/solvent–solvent interactions present in the HEF + PEGs binary mixtures. The Redlich–Kister (CNIBS/R–K) theoretical model predicts the experimental results obtained by solvatochromic probe studies in satisfactory manner. The results of the DFT and FTIR study also predict the possibility of the H-bonding interactions in HEF + PEGs mixtures.