Solute Dispersion in Soft Nanochannel under Streaming Potential-Mediated Pressure-Driven Flow

Article Type

Research Article

Publication Title

Industrial and Engineering Chemistry Research

Abstract

The present study investigates the dispersion of uncharged solutes in a soft nanochannel, an engineered device, with a particular emphasis on the influence of streaming potential under pressure-driven flow. A soft-step model is employed to account for the nonuniform distribution of monomers and the accompanying volume charge within the polyelectrolyte layer (PEL). The rigid channel walls are assumed to be hydrophobic and charged. Notably, ion-steric effects become significant for moderate to high charge conditions. Besides, the dielectric permittivity of the PEL is generally lower than that of the electrolyte solution, and hence, the ion partitioning effect becomes relevant. Based on these coupled electrostatic and hydrodynamic factors, we first analyzed the generation of streaming potential and the associated electrokinetic phenomena. The subsequent impact of streaming potential induced flow on the solute dispersion is then examined. Three models are adopted for this purpose: a general two-dimensional (2D) model for concentration distribution and a one-dimensional (1D) Gill model and a late-time Taylor–Aris (TA) model for area-averaged concentration. Dispersion is characterized by spatiotemporal concentration distributions, as well as the effective dispersion coefficient. A finite-difference based numerical method is used to solve the governing equations, and the results are validated against available experimental data as well as theoretical predictions under weak charge limits. To quantify the role of streaming potential-mediated axial flow, the findings are systematically compared to those for purely pressure-driven flow. We observe that the hydrodynamic dispersion depends strongly on the electrokinetic effects that directly regulate the generation of the streaming field. We have observed that the enhanced streaming potential field attenuates the overall fluid flow strength due to an increased opposing electroosmotic flow (EOF), resulting in less band dispersion. An increase in the PEL thickness enhances the flow resistance across the PEL, which also leads to a reduced fluid flow and hence reduces the convective dispersion of the solute band. The impact of the ion partition effect operational at the PEL-to-electrolyte interface, as well as the softness parameter of the PEL, is further illustrated. An enhanced flow strength is achieved while reducing the Debye–Hückel parameter due to less impact of streaming field-mediated opposing EOF, which further leads to an enhanced dispersion coefficient. Besides, the rise in hydrodynamic slippage can lead to a larger impact of the streaming field, which in turn leads to less dispersion of the solute band. Impact of the Péclet number on the dispersion process is further illustrated. This extensive study will thus be useful in practice to design robust nanofluidic separation systems.

First Page

23736

Last Page

23757

DOI

10.1021/acs.iecr.5c03990

Publication Date

12-10-2025

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