Molecular hydrodynamics for electro-osmosis in clays: from Kubo to Smoluchowski

For the sake of simplicity, the description of electrokinetic phenomenona is based on mesoscopic continuous solution models [Poisson-Boltzmann (PB), Navier-Stokes (NS), or Smoluchowski approaches]. We have compared these mesoscopic theories to microscopic descriptions (atomic and molecular level) in the case of hydrated montmorillonite clays. The distributions of solvent molecules and ions have been examined. They are found to be in agreement as long as the interlayer spacing is large enough. The electro-osmotic flow has been calculated too; it is shown that a slip length has to be taken into account. Slipping may have significant consequences for the general theory of electrokinetic phenomenona. Some of them are briefly described.