Electrokinetic flow in ultrafine slits: Ionic size effects

The equilibrium density profiles for the restricted primitive model (RPM) for electrolytes, which takes into account the ionic size, are used to calculate several electrokinetic quantities for a 1:1 ionic solution in a charged slit. The three-point-extension hypernetted-chain–mean-spherical equation is used to calculate the RPM density profiles. The results are compared to those obtained through the Poisson–Boltzmann equation for a point-ion model. Important quantitative and qualitative differences are found for ultrafine slits. These differences, as well as the general behavior of the electrokinetic quantities, are explained in terms of the structure of the electrical double layer inside the slit.