Determination of the NaCl electrolyte viscosity from reactive force field molecular dynamics simulations

The electrolyte flow in an Electrochemical Machining process can be modelled using the Navier-Stokes equations if the shear viscosity of the electrolyte is known. Apart from the possibility to measure the electrolyte viscosity, another option for the determination of the viscosity of a material is the application of molecular dynamics simulations. In the present work, molecular dynamics simulations with the modified reactive force field method RxAQ have been applied to obtain the shear viscosity of NaCl electrolyte. To this end, parameters for the RxAQ method have been optimised to characterise the motion of Na+ and Cl- ions in the aqueous environment. Subsequently, molecular dynamics simulations for water at temperatures between 280 K and 360 K and NaCl electrolyte with ion concentrations of up to 18% wt (at 300 K) have been performed. To determine the respective shear viscosity, the diffusion coefficients of the samples have been computed and the corresponding viscosities have been estimated by using the Stokes-Einstein relation. The results are compared to other calculations and measurements.