Investigating the molecular structure–property relationship in deep eutectic solvent and co-solvent systems through thermo physical measurements and FTIR spectroscopy

ABSTRACT A systematic investigation was undertaken to determine the thermodynamic properties of two binary mixtures comprising a deep eutectic solvent, (DES) specifically choline chloride/p-cresol at 1:2 molar ratio, with two distinct co-solvents: 2-ethyl-1-hexanol and 2-methyl-2,4-pentanediol. Density and viscosity were measured between 303.15 K to 313.15 K. Volumetric characteristics, including excess molar volume (VE) excess partial molar volumes, excess viscosity parameters like Δη and lnηE were computed. The study shows effect of temperature, co-solvent identity, DES composition and the implications of considering the DES as a mixture of its constituents. Analysis indicates molecular packing effects and hydrogen bonding interactions between the DES and the alcohol solvents contribution to volume contraction. The excess viscosity data underscored the significant role of hydrogen bonding in observed variations. The Jouyban-Acree model was applied for correlation which was assessed using the mean and individual relative deviation. The experimental data reliability was further substantiated through FTIR spectroscopic analysis.