Study of Solvation Behavior Thermodynamics and FT-IR Spectroscopic Analysis of N-Butylethanolammonium Based Ionic Liquids with Polar Solvents

Abstract

The effect of anion geometry on aggregation behavior of surfactant with aqueous solutions was investigated by the systematic measurements of concentration, temperature dependent density and derived thermodynamic properties. In this work, N-Butylethanolammonium trifluoroacetate [BEATFA] and N-Butylethanolammonium nitrate [BEAN] ionic liquids (ILs) were synthesized and characterized by 1H NMR. The binary systems IL+water/ethanol were prepared for the concentration ranges from 0.0264 to 0.4621 mol·kg−1 and the temperature ranges from 298.15 K to 318.15 K. Further, the apparent molar volume (Vɸ), partial molar volume (Vɸ∞), thermal expansion coefficient (α) and apparent molar expansivity (Eɸ) were derived from the experimentally measured density data. The critical aggregation concentration (cac), apparent molar volume at critical aggregation concentration (Vɸ,CAC), apparent molar volume in aggregation phase (Vɸ,mic), change in apparent molar volume due to aggregation (∆Vɸ,m) and degree of ionization (α′) were derived from the plot of apparent molar volume versus inverse of ILs concentration. The thermodynamic aggregation properties such as standard Gibb's free energy of micellization (∆Gom), standard enthalpy of micellization (∆Hom) and standard entropy of micellization (∆Som) were calculated from experimental measurements. The sign and magnitude of apparent molar volume at infinity dilution reveals about IL+solvent or IL-IL interactions between the component molecules. The system [BEAN]+water showed lowest positive magnitude in both Vɸ∞ and cac than compare to [BEATFA]+water due to the formation of stronger IL+solvent intermolecular interactions through the H-bonding. The variance in observed Vɸ∞ and cac data with different solvents due to the solvophobic effect and hydrogen bonding tendency was explained by FT-IR spectroscopy and DFT computational study. Among the all binary systems, [BEAN]+water showed highest intermolecular interaction tendency than other systems, the obtained results were compared with available literature data and analyzed in terms of intra and intermolecular interactions, polarity of solvents, hydrophobicity, nature anion, size and shape of the anion.