Thermophysical and spectroscopic studies of room temperature ionic liquid (1-hexyl-3-methylimidazolium bromide) with ethylene glycol oligomers

Ionic liquids (ILs) or their mixtures with cosolvents are becoming increasingly important topics in the current context as the world moves towards sustainable energy generation. Thermodynamic and transport properties were measured to understand the nature and behaviour of molecular systems in liquid mixtures. These properties are crucial from both practical and theoretical viewpoints to understand liquid theories. This study focuses on analysing thermophysical properties such as density (rho), viscosity (eta), refractive index (nD) and their correspondingly derived properties as excess molar volume (VEm), deviation in viscosity (Delta eta), deviation in refractive index (Delta phi nD) and excess thermal expansivity coefficient (alpha E). Additionally, activation parameters for viscous flow including activation energy (Ea), excess Gibbs energy (Delta G*E), excess enthalpy (Delta H*E) and excess entropy (Delta S*E) are investigated. The considered compounds included the IL 1-hexyl-3-methylimidazolium bromide [HMIM]Br and four ethylene glycol oligomers (mono/di/tri/tetra-ethylene glycol) over a temperature range of 298.15 to 313.15 K. The Redlich-Kister equation was used to estimate the standard deviation between experimental and calculated excess properties. The VEm data was further explored using Prigogine-Flory-Patterson (PFP) and Graph theories to elucidate deviations in thermophysical properties of the mixtures. The correlation of experimental VEm data was satisfactory in terms of the sign and magnitude compared to calculated data. The viscosity values were further examined by different correlations and their corresponding average standard deviation percentages (ASD%) were considered to determine the efficacy of these correlations. Fourier Transform InfraRed (FT-IR) and Raman Spectra are recorded to provide supportive information on the assumed topologies for the components in their pure and mixed states. The results provide thermodynamic guidance to design chemical processes for various industrial procedures.