Experimental and theoretical studies to investigate molecular interactions between ethylene glycol oligomers and 1-butyl-3-methylimidazolium bromide

The thermophysical characteristics of pure liquids and their mixes are substantial in applied as well as theoretical research. This paper presents the measured data on: density ($\rho$), viscosity $\left(\eta \right)$, refractive index ($n_D$) and consequent calculated parameters: {excess molar volume ($V_m^E$), partial molar volume (${\overline{V}}_m$), excess partial molar volume (${\overline{V}}_m^E$), deviation in viscosity $\left(\Delta \eta \right)$, excess Gibbs energy of activation of viscous flow ($\Delta G^{\ast E}$), deviation in refractive index (${\Delta }_{\varphi }{n}_D$) and deviation in molar refraction (${\Delta }_x{R}_M$)} of binaries containing 1-butyl-3-methylimidazolium bromide ([BMIM]Br) with glycol oligomers (mono/di/tri/tetra-ethylene glycol) at T/K = 298.15–313.15 and pressure p/MPa = 0.1. The Redlich-Kister equation efficiently estimates the standard deviation between the experimental and calculated excess properties. The interactions between constituents were considered while interpreting the obtained results. The values of $V_m^E$, ${\overline{V}}_m^E$, $\Delta \eta$, ${\Delta }_{\varphi }{n}_D$ and ${\Delta }_x{R}_M$ exhibited negative trends throughout the range, whereas $\Delta G^{\ast E}$ values displayed a sigmoidal shift (negative to positive) with increasing [BMIM]Br concentration. The $V_m^E$ data has been explored in terms of Prigogine-Flory-Patterson (PFP) and Graph theories to elucidate the deviations in thermophysical properties of the mixtures caused by variations in strength and magnitude of interactions. Additionally, the $\eta$ values were correlated using ten models and their correlation ability has been perceived via the average standard deviation percentage. The pure and binary mixtures were also spectroscopically examined using Fourier Transform InfraRed (FT-IR) and Raman spectroscopy to elucidate the structural variations.