Surface tension of oxygen–nitrogen mixture: molecular simulation

Abstract

The surface tension of the oxygen–nitrogen mixture was estimated by molecular dynamics in a canonical ensemble. The covered temperature range was [60–120]K. Our results were compared with the available experimental data, exhibiting an excellent agreement. We achieved such agreement by two methods, one of them was to include a constant factor x =0.9433 into the energetic cross term of the Lorentz–Berthelot combining rules using the TraPPE force field for both species. The second method consisted in modifying the original TraPPE force field used for each type of molecule in order to reproduce the experimental surface tension and the vapour pressure at the same time, as pure fluids. These same modified force fields were used to calculate surface tension curves for the binary mixture, which showed an excellent agreement with experimental data for all considered temperatures. Therefore, it was not necessary to modify the cross term of the combining rules. In addition, the vapour pressure, as a function of nitrogen mole fraction, was estimated; our data were consistent with the experimental evidence. Finally, the surface tension, as a function of vapour pressure, was calculated and compared with available experimental data, and a good agreement was observed as well.