During the past few years, there has been a surge in interest and research in the arena of utilizing deep eutectic solvents (DESs) as green solvents. This manifested in applying DESs in a variety of industrial applications. Most of the reported work in this field was directed toward the choline chloride-based DES. Recently, the area of DES synthesis was widened by considering other quaternary ammonium and phosphonium salts. In this work tetrabutylammonium chloride (TBAC) is used as a salt for the synthesis of three different DES systems based on three different hydrogen bond donors (HBDs), namely, glycerol, ethylene glycol, and triethylene glycol. Screening tests for each DES system was performed to identify salt:HBD ratios that exhibit a minimum freezing point, and at least three such ratios were selected for each system. Physical properties including melting point, density, viscosity, surface tension, refractive index, conductivity, and pH were measured for the three DES systems at different temperatures ranging from (293.15 to 353.15 K). It is worth mentioning that this class of DES exhibits a wide range of properties that can be tailored toward specific chemical and other engineering applications.

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Abstract-Deep

In this work, a viscosity model for choline chloride-based deep eutectic solvents (DESs) was developed. In addition to temperature, the new model presented here considers the composition of the salt in the DES, which was not the case for all previously reported viscosity models. Two forms of the proposed model were optimized and fitted to viscosity experimental data. The developed model was tested using the experimental viscosity values for nine common choline chloride-based DES systems of different hydrogen bond donors. The performance of the model was evaluated using three different statistical indicators, namely average relative deviation, correlation coefficient (R 2 ) and standard deviation. In addition, a significance t-test was also conducted on each of the fitted DES viscosity data. The statistical indicators showed a very good agreement between the model-predicted viscosity and the experimental viscosity values for the DESs with relatively low viscosities (DES1, DES2, DES4 and DES5). For DESs with high viscosities (DES3, DES7, DES8 and DES9), the second model gave better predictions. Overall, this proposed model was capable of predicting DES viscosities for different salt compositions at different temperatures as supported by the statistical significance t-test and other statistical indicators.

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