Is Stokes-Einstein relation valid for the description of intra- diffusivity of hydrogen and oxygen in liquid water?
IN Tsimpanogiannis and OA Moultos, FLUID PHASE EQUILIBRIA, 563, 113568 (2022).
In this study, all available data from experiments and molecular simulations for the intra-diffusivities of H-2 and O-2 in H2O, and for the self-diffusivity of pure H2O are analyzed to examine the validity of the Stokes-Einstein relation. This analysis is motivated by the significant amount of work devoted through the years for improving the predictions of intra-and self-diffusivities in binary and multi- component mixtures relevant to chemical and environmental processes. Here, we calculate the slopes s and t corresponding to the ln(D) vs. ln(T/eta) and ln(D/T) vs. ln(1/eta) plots, respectively, where D is the intra-diffusivity, eta the viscosity, and T the temperature of the T/eta systems. Our results show that s and t deviate from unity no matter if the experimental or simulation data are used. This means that the Stokes-Einstein relation is violated for the binary systems of H-2 and O-2 with H2O, and for pure H2O. Although prior studies mainly focused on re-evaluating the parameter A of the SE-based semi-theoretical/semi- empirical approaches expressed as D = A T/eta, our results indicate that reliable predictions for the intra-and self-diffusivities can be achieved by improving the accuracy of the prediction of slopes s and t.
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