We have studied mixtures of alcohol and water in an extensive series of 465 molecular-dynamics simulations with an aggregate length of 713 ns, in order to study excess properties of mixing, in particular the relation between mobility and viscosity. Methanol/water, ethanol/water, and 1-propanol/water mixtures were simulated using an alcohol content of 0–100 mass % in steps of 10%, using the OPLS (optimized potential for liquid simulations) force field for the alcohol molecules and the TIP4P (transferable intermolecular potential with four particles) water model. Computed densities and energies show very good agreement with experimental data for bulk simulations and the mixtures are satisfactory as well. The shear viscosity was computed using nonequilibrium molecular-dynamics simulations. Other properties studied include diffusion constants and rotational correlation times. We find the mobility to correlate well with the viscosity data, i.e., at intermediate alcohol concentrations the viscosity is maximal and the mobility is minimal. Furthermore, we have combined the viscosity and diffusion calculations in order to compute an effective hydrodynamic radius of the particles in the mixtures, using the Stokes–Einstein relation. This analysis indicates that there is no collective diffusion of molecular clusters in these mixtures. For all properties we find that the excess values are underestimated in the simulations, which, given that the pure liquids are described rather well, raises the question whether the potential function is too simplistic to describe mixtures quantitatively. The set of simulations presented here can hence be regarded as a force-field benchmark.
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8 October 2003
Research Article|
October 08 2003
Dynamic properties of water/alcohol mixtures studied by computer simulation
Erik J. W. Wensink;
Erik J. W. Wensink
Department of Physics, University of Bergen, Allégatan 55, N-5007, Bergen, Norway
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Alex C. Hoffmann;
Alex C. Hoffmann
Department of Physics, University of Bergen, Allégatan 55, N-5007, Bergen, Norway
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Paul J. van Maaren;
Paul J. van Maaren
Department of Cell and Molecular Biology, Uppsala University, Husargatan 3, Box 596, SE-751 24 Uppsala, Sweden
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David van der Spoel
David van der Spoel
Department of Cell and Molecular Biology, Uppsala University, Husargatan 3, Box 596, SE-751 24 Uppsala, Sweden
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J. Chem. Phys. 119, 7308–7317 (2003)
Article history
Received:
June 18 2003
Accepted:
July 17 2003
Citation
Erik J. W. Wensink, Alex C. Hoffmann, Paul J. van Maaren, David van der Spoel; Dynamic properties of water/alcohol mixtures studied by computer simulation. J. Chem. Phys. 8 October 2003; 119 (14): 7308–7317. https://doi.org/10.1063/1.1607918
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