Presence of a Molecular Ligand alters the Solvent Behavior of an Ionic Liquid: A Combined Physicochemical Properties, FTIR Spectroscopy and Dynamic Light Scattering Investigation

The physicochemical properties of an ionic liquid (IL) based extraction system depends on the type of cation and anion present and the type of extractant dissolved in it. In this paper, we have investigated the solvent behavior of a ionic liquid based system comprising of a diglycolamide based extractant: T2EHDGA (N,N,N',N'-tetra(2-ethylhexyl) diglycolamide) dissolved in an imidazolium based ionic liquid: [C(4)mim][NTf2] (1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide). The properties of IL systems such as dynamic viscosity (eta) and density (rho) were measured as a function concentration of T2EHDGA, nitric acid and the experimental temperature using a rolling ball viscosmeter and a U-tube densitometer. Viscosity and density of IL phase increase and decrease respectively in the presence of ligand in it. Dynamic Light Scattering (DLS) results obtained by DLS spectrometer inferred the aggregation behavior of IL phase and the average aggregate size of IL increases in presence of T2EHDGA. The water uptake by IL phase upon acid equilibration inferred from FTIR spectroscopy specified a decrease in visocisty and density of the solvent. The evaluation of molecular volume (V-m) and standard entropy (S-o) offered higher values for T2EHDGA as compared to [C(4)mim][NTf2] whereas, the lattice potential energy (U-Pot) showed reverse trend. The refractive index (n) of T2EHDGA/IL mixture measured by a refractometer suggested the considerable changes in presence of T2EHDGA and nitric acid.