Structural and interactional behaviour of aqueous mixture of room temperature ionic liquid; 2-hydroxyethyl-trimethylammonium l-lactate

•Thermophysical and spectroscopic properties of aqueous mixtures 2-[HE3MA]LAC have been measured.•Effect of temperature on thermophysical properties has also been studied.•Stronger intermolecular have been observed between [HE3MA]LAC and H2O.•Magnitude of interactions decreases with the rise in temperature.•Spectroscopic studies shows interactions between -N+-(CH3)3-N+-(CH3)3 with -OH--OH- group and COO− with H+ of IL and H2O.

In order to understand the molecular interactions between the green solvent system, (water + lactate based ionic liquid); 2-hydroxyethyl-trimethylammonium l-lactate ([(C2H4OH)(CH3)3N][Lactate]), the thermophysical properties viz. density ρ, speed of sound u, specific conductivity κ, refractive index nD and spectroscopic properties viz. IR, 1H and 13C NMR have been investigated over the whole composition range at atmospheric pressure with temperature varied from (293.15 to 323.15) K. To gain more insight of intermolecular interactions occurring in the aqueous mixture of [(C2H4OH)(CH3)3N][Lactate], intermolecular free length Lf, acoustic impedance Z, relative association RA, excess molar volume VE, deviations in isentropic compressibility ΔKS  , partial molar excess volume ViE, partial molar deviations in isentropic compressibility ΔKS,i, deviation in specific conductivity Δκ and deviation in refractive index ΔnD have been predicted as a function of IL concentration over the whole composition range. These results have been fitted to the Redlich–Kister polynomial. A large deviation from ideality has been observed on mixing water and [(C2H4OH)(CH3)3N][Lactate] which are due to the formation of strong intermolecular hydrogen bonding between the two molecules. Also, it has been noticed that the mixture of water and [(C2H4OH)(CH3)3N][Lactate] became warm that indicates mixing of these two components is exothermic. Thermodynamic and spectroscopic data provide valuable information that is of remarkable importance for various technological applications, particularly for electrochemical applications, as capacitors, fuel cells and batteries.

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