Effect of 1-alkyl-3-methylimidazolium bromide on thermodynamic and transport properties of azeotropic mixtures of water + ethanol at 298.15 K

This study investigates the thermodynamic and transport properties of 1-alkyl-3-methylimidazolium bromide ionic liquids, [BMIM][Br] and [HMIM][Br], in water, ethanol, and their binary mixtures at 298.15 K, focusing on density, speed of sound, and viscosity. Experimental data reveal that these properties increase with ionic liquid concentration, with water enhancing solvation due to its polarity and ethanol promoting denser solvent structures. The Pitzer-Debye-Hückel (PDH) model accurately correlates apparent molar volume Vφ and isentropic compressibility κφ, showing higher Vφ0 in water (e.g., 170.20 × 10⁻⁶ m³·mol⁻¹ for [BMIM][Br]) than ethanol, and non-linear behavior in mixed solvents. The negative κφ0 for [HMIM][Br] in ethanol (-13.70 × 10⁻⁶ m³·mol⁻¹) indicates rigid solvation, contrasting with compressible shells in water-rich mixtures. The ePC-SAFT model predicts density and speed of sound with superior accuracy in mixed solvents (e.g., 0.0439% ARD for [HMIM][Br]), with binary interaction parameters kij and γ highlighting complex ion-solvent interactions. The Jones-Dole model elucidates viscosity, revealing strong ion-ion interactions and structure-making in water for [BMIM][Br], with structure-breaking in water-rich mixtures for both ionic liquids. Low standard deviations across models confirms their reliability. The hydrophobic hexyl chain in [HMIM][Br] significantly influences solvation, emphasizing the role of ionic liquid structure and solvent composition. These findings are crucial for optimizing ionic liquids in chemical engineering applications, such as electrolyte design and solvent selection, and pave the way for future studies exploring temperature effects, additional solvent systems, and advanced modeling to enhance predictive accuracy and application versatility.