Electroosmotic Dispersion of Uncharged Solutes through a Nanochannel

The present study investigates the modulation of electroosmotic flow (EOF) within a nanochannel and its impact on the dispersion of uncharged solutes. We examine configurations where the channel walls are either similarly or oppositely charged. To account for wall hydrophobicity, we employ a model where the hydrodynamic slip length is modulated by the surface charge density. By varying the background electrolyte concentration, we explore regimes ranging from significant electric double layer (EDL) overlap to negligible overlap. The EOF is further modified by incorporating ion steric effects. We utilize this modulated flow field to analyze the convective-dispersive transport of an uncharged solute, initially released as a pulse of finite bandwidth. The dispersion process is evaluated using three distinct frameworks: a comprehensive 2D convective-diffusion model, the 1D Gill and Sankarasubramanian (GS) dispersion model, and the Taylor–Aris (TA) dispersion model (valid in the long-time limit). We demonstrate the influence of pertinent parameters that regulate the EOF modulation as well as the dispersion process. Besides, a detailed analysis of the impact of Péclet number on the overall dispersion dynamics is made. Furthermore, a comparative analysis between the 1D and 2D dispersion models is conducted. The results of this work offer a robust framework for predicting and controlling solute dispersion in nanofluidic systems, particularly when surface effects and modulated flow fields are significant.