Physical-chemical Properties Of Pseudo-binary System Of TEAB-EG Deep Eutectic Solvent With Molecular Solvents

In recent years,deep eutectic solvents have developed rapidly,showing an all-round cross-field application trend.It has unlimited structural possibilities,and its physicochemical properties can be adjusted by adjusting the hydrogen bond donor and hydrogen bond acceptor or their molar ratio.In addition,the introduction of other molecular solvents into the deep eutectic solvent has become a way to expand the application and alleviate the high viscosity problem and save the cost.Starting from the physicochemical properties of pseudo-binary mixtures,such as density,viscosity,surface tension,refractive index and conductivity to explore the solute-solvent interaction in the mixture system is of great significance for research in this field and provides information for industrial applications.1.In this paper,DES（1 TEAB:3 EG）was synthesized,and it was characterized by ~1H NMR,infrared and thermogravimetry,and the water content was measured at the same time.Then,a pseudo-binary system with the full concentration range（x₁=0.0000-1.0000）at 288.15 K～318.15 K was prepared using DES（1 TEAB:3 EG）and molecular solvents（acetonitrile,ethanol and water）.The density,surface tension,refractive index,viscosity and conductivity of the pseudo-binary systems were also tested.After comparing with the literature value,the experimental values are within the allowable range of error,and the result shows that the experimental level of this paper meets the requirements of scientific research.2.Then,based on the measured density values,the interaction between the deep eutectic solvent and the molecular solvent was explored.From the obtained average molar volume,thermal expansion coefficient,excess thermal expansion coefficient and excess molar volume of the pseudo-binary mixture,it can be found that the average molar volume of the pseudo-binary system increases with the increase of the mole fraction and changes with the increase of the temperature.The thermal expansion coefficient of the pseudo-binary system increases with the increase of temperature,the compound with organic solvent decreases with the increase of mole fraction,and the compound with water increases with the increase of mole fraction.In the full concentration range,the excess molar volume and the DES mole fraction were fitted by the RK equation,and the excess molar volume V^E was negative,and the force was the strongest at the lowest point.Related to hydrogen bonding and molecular structure.In addition,for organic solvents,the excess molar volume decreases with increasing temperature,and the higher the temperature,the greater the force.For water,the excess molar volume increases with increasing temperature,the higher the temperature the weaker the force.The value of the partial volume of infinite dilution is negative for both the molecular solvent and DES,so both components tend to be dissolved by the other,but this tendency is more pronounced for water molecules.powerful.In addition,the values of excess partial molar volume at infinite dilution for both water and DES tend to be positive with increasing temperature.This suggests that the solvation propensity in the mixture decreases as the temperature increases,and thus,the hydrogen bonds established at higher temperatures are weaker than those established at lower temperatures.In contrast,the trend was reversed between DES and acetonitrile or ethanol.3.The surface tension deviation was calculated based on the surface tension value,and the interaction between deep eutectic solvent and molecular solvent was explored.Based on the improvement of Li surface model,a thermodynamic model of the surface tension of the pseudo-binary system in the full concentration range is proposed,and a new function of the molar surface free energy g_s of the pseudo-binary mixture is obtained.Furthermore,the temperature has little effect on the excess molar surface Gibbs free energy.The new E（?）tv（?）s equation is successfully extended to the pseudo-binary system.Compared with the traditional E（?）tv（?）s equation,each parameter of the new E（?）tv（?）s equation has a clear physical meaning:the negative value of the slope is the molar surface entropy,and the intercept is the molar surface enthalpy,the molar surface enthalpy varies little with temperature in a mixture of a given mole fraction.The refractive index deviation was also calculated using the refractive index values to enhance the analysis of intermolecular interactions.4.According to the Arrhenius equation,the viscosity of the pseudo-binary mixture is nonlinearly fitted to the temperature.The viscosity of the DES pseudo-binary mixture decreases gradually with the increase of temperature,and the viscosity value decreases with the increase of temperature.A new concept of relative viscosityη_r of pseudo-binary mixtures is proposed.On the basis of the concept of relative viscosityη_r,the calculation formula of the Gibbs free energyΔG^≠E for the excess viscous flow of pseudo-binary mixtures is obtained,which is consistent with the experimental phenomenon of viscosity deviation.The Redlich-Kister polynomial was used to fit the relationship between the activated Gibbs free energyΔG^≠E and the mole fraction x₁,and the fitting effect was good.The ionicity of the pseudo-binary system was analyzed by using the conductivity and viscosity values and referring to Walden’s rule.The mixture close to the reference line is a"good ionic"liquid,while the underside of the liquid away from the diagonal is a"weakly ionic"liquid.The"non-ionic"liquid is in the lower half,far from the diagonal.Therefore,rich DES is more ionic than compounded with solvent.