Soret coefficients and thermal conductivities of alkali halide aqueous solutions via non-equilibrium molecular dynamics simulations

Thermal gradients induce thermodiffusion, the Ludwig-Soret effect, which might be exploited in biotechnological, chemical, micro and nanofluidic applications. It has been shown that thermodiffusion depends very sensitively on the nature of the solute, suggesting that water-solute interactions play an important role in determining the preference of solutes to move towards hot or cold regions. Here we employ non-equilibrium molecular dynamics computations to gain insight into the role of water-ion interactions on the strength and sign of the Soret coefficient of alkali halide solutions. By performing simulations with different force-fields, we draw conclusions on the dependence of the thermodiffusive response with the properties of the first hydration shell of the ions. We further compute the thermal conductivity of aqueous solutions. State-of-the art force-fields reproduce the decrease of the thermal conductivity with increasing salt concentration when the thermal conductivity of pure water is corrected to match experimental data.