Nonideal Behavior of Aqueous Deep Eutectic Solvents Based on Tetrabutylphosphonium Bromide and Ethylene Glycol/Glycerol

Understanding the effect of solvents on the thermophysical properties of deep eutectic solvents (DESs) is crucial to utilize their green credentials in several industrial processes. Herein, we explore the nonideal behavior of aqueous DES mixtures to better understand the prevailing intermolecular interactions within them. The used DESs are composed of tetrabutylphosphonium bromide and ethylene glycol/glycerol. The nonideal behavior is explored through calculating the excess molar volume (VmE) and viscosity deviation (ln ηm) over the entire range of compositions and the temperature range from 293.15 to 323.15 K at 101.3 kPa pressure. The values of VmE and ln ηm are fitted with the Redlich–Kister-type polynomial equation. The negative VmE and ln ηm values indicate the strong H-bonding interactions between the DES and water and destruction of the DES structure. The experimentally calculated values of VmE are further evaluated using the well-known Prigogine–Flory–Patterson (PFP) theory and extended real association (ERAS) model. Looking at their increasing utilization, we believe that the results of the present study will be beneficial for designing various industrial equipment and processes.