In this work, we theoretically investigate the implications of streaming potential on the transport and size-based separation of charged solutes in nanoscale confinements. By employing a regular perturbation analysis, we demonstrate that the consideration of streaming potential establishes a new paradigm of size-based separation of charged solutes in nanochannels. Depending on the sizes of the particles being handled, we establish two distinctive separation regimes. For smaller particles with significantly large electrophoretic mobilities, electrophoretic transport mechanisms predominantly influence the solutal transport characteristics, whereas for larger particles the combined pressure-driven and back electroosmotic transport mechanisms essentially dictate the resultant separation characteristics. The extent of improvement in separation characteristics, on account of the consideration of streaming effect, largely depends on the consideration of particle-wall interactions. For cases without wall effects, the streaming potential may induce dramatic enhancements in the resolution of separation for small particles by exploiting optimal combinations of zeta potential values and relative thicknesses of the electrical double layers. However, with wall effect considerations, similar combinations of zeta potential and electrical double-layer thicknesses may give rise to dramatic improvements in the separation characteristics over a much wider range of particle sizes by interacting nontrivially with the streaming potential effects. Such confluences may be exploited in practice for designing efficient nanofluidic separation systems.
Adsorption Electrochemistry