Effect of water and hydrogen bond acceptor on the density and viscosity of glycol-based eutectic solvents

Deep eutectic solvents (DESs) have been studied as promising solvents for several processes because of their favorable properties, such as biodegradability, tuneability, and low cost. In recent times, DESs have gained attention for their potential applications in various fields. Therefore, it is essential to characterize the physicochemical and transport properties of DESs and understand their interactions with other solvents. In this study, DESs were prepared with betaine as the hydrogen bond acceptor (HBA) and a glycol (e.g., ethylene glycol, 1,2-propanediol, 1,3-propanediol, or 1,4-butanediol) as the hydrogen bond donor (HBD) in different molar ratios. The density and viscosity of the DESs were measured over a temperature range of 20 °C - 60 °C at 101.3 kPa. Under the same conditions, density and viscosity were measured for the DES + water mixtures at a DES HBA:HBD molar ratio of 1:6. Also, the choline chloride-based DESs at HBA:HBD molar ratio of 1:3 (all the previously mentioned glycols) and 1:6 (only ethylene glycol) were measured at different water contents to evaluate the effect of the HBA on the same properties. PC-SAFT and Free Volume Theory (FVT) were used, respectively, to model the density and viscosity measurements to assess the effect of changing the temperature, the chain length of the HBD, and the water content. Furthermore, classical molecular dynamics simulations were performed to obtain molecular insights into the mixtures and their solvation with water. The molecular information for these solvents, provided by the models fed from the performed experiments, allows for reducing the further experimental load when designing chemical processes.