Electro-diffusio-osmosis in an anisotropic channel

Abstract

Solute dispersion i.e., the combined result of convection and diffusion, within the electroosmotic flow, holds immense promise for diverse applications spanning lab-on-a-chip devices, biomedical engineering, and hydrocarbon production. Beyond mere diffusion, the concentration gradient of an external solute can significantly influence fluid flow. In the present study, the fluid flow driven by the osmotic pressure gradient induced simultaneously by the concentration gradient (diffusioosmosis) and the externally applied electric potential (electroosmosis) in an anisotropic porous microchannel is theoretically analyzed. The classic Taylor’s dispersion model governs the solute dynamics where the initial Gaussian distribution of the solute induces the diffusioosmotic pressure gradient. The momentum balance and advection–diffusion equations are coupled with the diffusioosmotic slip boundary conditions. The multi-time scale approach is used to obtain the closed-form solution of the flow dynamics, which further are utilized to study the behavior of the first-order corrections of the flow dynamics with various vital parameters. Initially, the flow is driven by the electric potential gradient, which contributes to the solute’s transport via convection. The mechanism at any non-zero time is similar, but the additional convection the solute experiences is due to the flow of solvent owing to the solute concentration gradient. This recurring complex phenomenon is thoroughly examined and illustrated graphically. The competing nature of electroosmotic convection against diffusioosmosis is observed, resulting in particle trapping, which can be helpful for applications including particle mixing and separation. The first-order solute concentration for the combined electro-diffusio-osmotic flow surpasses that observed in either pure electroosmotic or pure diffusioosmotic scenarios. The electroosmotic and diffusioosmotic driving forces can be precisely modulated through system parameters, offering a controllable platform for particle transport, which could be a promising avenue for advanced drug delivery systems and optimized microfluidic environments where precise control over particle trajectories is critical.