Abstract
Based on the molecular dynamics method, the calculations for diffusion coefficients were carried out in binary aqueous solutions of three alcohols: ethanol, isopropanol, and tert-butanol. The intermolecular potential TIP4P/2005 was used for water; and five force fields were analyzed for the alcohols. The force fields providing the best accuracy of calculation were identified based on a comparison of the calculated self-diffusion coefficients of pure alcohols with the experimental data for internal (Einstein) diffusion coefficients of alcohols in solutions. The temperature and concentration dependences of the interdiffusion coefficients were determined using Darken’s Equation. Transport (Fickian) diffusion coefficients were calculated using a thermodynamic factor determined by the non-random two-liquid (NRTL) and Willson models. It was demonstrated that for adequate reproduction of the experimental data when calculating the transport diffusion coefficients, the thermodynamic factor has to be 0.64. Simple approximations were obtained, providing satisfactory accuracy in calculating the concentration and temperature dependences of the transport diffusion coefficients in the studied mixtures.
Highlights
Physicochemical properties of aqueous solutions related to alcohols have for a long time been a subject of close study due to their wide application in various industries and human activity
This is due to specific intermolecular interactions that occur between the molecules of alcohol and water
Internal diffusion coefficients have been calculated under equilibrium conditions depending on the concentration and temperature for force fields FF-1 and FF-2
Summary
Physicochemical properties of aqueous solutions related to alcohols have for a long time been a subject of close study due to their wide application in various industries and human activity. The accuracy of the data obtained as a result of molecular simulation is largely determined by the force fields used for description of intermolecular interactions. In the present work, based on molecular dynamic simulation, the diffusion coefficients for water-alcohol mixtures of three alcohols were calculated: ethanol, isopropanol, and tert-butanol. The analysis of literature data showed that the ethanol-water mixture has been more explored than aqueous solutions of isopropanol and tert-butanol They are, as a rule, limited to simulation at one temperature and, less often, to simulation at two temperatures. In the paper, based on a comparison of the results of molecular simulation with a physical experiment on the coefficients of self-diffusion and internal diffusion, we analyzed the accuracy of calculating several promising force fields selected on the basis of an analysis of literature data. A similar analysis with the use of the all-atom potential for water-alcohol rats was carried out in [28,29,30,31,32,33,34,35,36,37]
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