Diffusivity effects on charged species separation in nanochannels

Recent work has investigated the dispersion and separation of charged molecules in nanochannels. One conclusion has been that the combination of transverse velocity and electric field gradients can provide a mechanism for separation of different-valence ionic species. Building on this, we present a continuum transport model for finite-sized particles in a nanofluidic system and analyze the model both theoretically, with Taylor-Aris dispersion theory, and computationally, with direct numerical simulation. We assume a finite-sized electric double layer, a dilute solution, and an axially applied DC electric field. We show that, under these conditions, finite-sized particles may exhibit qualitatively different separation behavior than predicted by small ion theory.