Fitting of experimental viscosity to temperature data for deep eutectic solvents

Seven new deep eutectic solvents (DESs) based on tetrabutylammonium bromide (TBAB) and tetraethylammonium p-toluene sulfonate (TEAPTS) were prepared and their viscosity determined between 298.15 and 323.15 K. The effect of temperature was modeled using an appropriate fitting procedure, proposed in this work, with a coefficient of determination R-2 > 0.99 for all DES. The fitting procedure used of preexisting experimental data in which 70 DESs were collected from the literature and refined on the basis of R2 and root mean square error (RMSE); similar to 10% of the data was rejected. Furthermore, about half of the refined data was fittedwith a three-parameter Vogel-Fulcher-Tammann (VFT) equation with an R-2 higher than 0.99. The remaining dataweremore adequately fittedwith a two-parameter Arrhenius equation. The adjusted parameters of both models for 62 DESs were determined to estimate the viscosity. Based on R2, the VFT model was more accurate than the Arrhenius model. Moreover, additional in-lab experiments were performed for model validation at six temperatures (from 298.15 to 323.15 K). In some cases, the experimental measurements were different from those in the literaturewith an R-2 below 0.95 indicating a large scatter in the viscosity data. Most of the highly viscous DESs considered in this study showed a rapid decay when temperature increases. Hence, the limitation of using these solvents for applications such as absorption could be overcome by operating at slightly higher temperature (i.e., 313.15 to 333.15 K). (C) 2020 Elsevier B.V. All rights reserved.