Molecular Dynamics Parametric Study of Electrokinetic Transport in Silicon Nanochannel

Jelinek, B., Felicelli, S. D., Mlakar, P. F., & Peters, J. F. (2009). Molecular Dynamics Parametric Study of Electrokinetic Transport in Silicon Nanochannel. USACE Research and Development Conference 2009. Memphis, TN.

Numerical models of electrokinetic process help to improve current technological devices and guide the design of new technology based on the principles of electrokinetic transport in materials including concrete. Possible applications of the electrokinetic process in concrete are decontamination, dewatering of concrete structures, and electrical deposition of protective nanoparticles to prevent corrosion or to eliminate alkali-silica reaction. The main driving force of electrokinetic transport occurs in an electric double layer (EDL) at the solid liquid interface, which has nanoscale dimensions. The continuum theory, based on the Poisson-Boltzmann and the Stokes equation, cannot capture the phenomena in the EDL, which leads to inaccurate predictions in the microscale transport or to failure in the explanation of some phenomena observed at the macroscale. To account for the nanoscale interactions at the pore walls resulting from the effects neglected in the classical Poisson-Boltzmann equation, corrections in the parameters of continuous model that change the ion concentration can be introduced, following the method of Qiao and Aluru. We studied temperature effects on the electrokinetic transport in the nanochannel with a slab geometry using a molecular dynamic (MD) model. A simple, previously published system consisting of Na+ and Cl- ions dissolved in water and confined between fixed crystalline silicon walls with negatively charged inner surfaces in an external electric field was chosen as a benchmark. MD force fields were used to model the interaction between ions, water molecules and wall atoms in the EDL region. Dependence of the fluid flow on the temperature and thermostating techniques was examined. The variation of resulting areal mass flux density and molecular velocity profiles across the channel with initial conditions was explored to asses the statistical significance of the results. It was found that, at least at the size scale, surface charge density, electric field and ionic concentrations of the benchmark system, the water flux and even its direction are directly controlled by temperature. Results indicate that classical MD simulations can supply information to refine the continuum modeling of the electrokinetic transport in concrete nanopores.