Interaction between Polymer Molecules and Fluid Dynamic Response at Varied Ph Scenarios in Induced Charge Electroosmosis

Abstract

Induced charge electroosmosis (ICEO) can assist lab-on-a-chip devices and macromolecular separation involving the interface, pH, and solution properties. To supplement the mechanistic insights into the ICEO phenomenon in complex electrochemical scenarios, we numerically simulate electrokinetic ion transport–fluid flow coupling regulated by solution pH and polymer macromolecular rheology around a polarized cylinder. The physics of the ICEO is analyzed in multiple insights, which involve the azimuthal velocity, flow type, energy distribution, interfacial ion transport, and electroelastic instability. The main findings are as follows: (1) Deviations in neutral pH conditions cause flow field asymmetry and alter the input energy distribution (PE) in the tight double layer. Polymers greatly modify the interfacial force features in ion-enriched regions, as identified by the first stress difference (N1). (2) The kinetic energy vs. viscosity ratio (β) represents the nonlinear enhancement curve Ek = 0.011*exp(-β/-0.64)-0.0138 due to the weakened effective viscosity Rvis (the ratio of the effective total viscosity to the initial viscosity). Besides, shear thinning notably lifts the charge density and salt concentration at cylinder surface, which boosts the PE. (3) Quadrupolar vortex modes impact the positive correlation between β and the ion current (Jtotal) at different pH levels, resulting in less ion current dependence in small β. A low enhancement efficiency occurs at 10-4 ≤ α (molecular anisotropy) ≤ 0.1, whereas a high efficiency exists at α > 0.1. Electroelastic instabilities are confirmed by the spatiotemporal evolution of the velocity fluctuation, with a broadband structural power-law decline in the power spectral density. These results allow microdevice mixing manipulation and disclose non-Newtonian barrier of electrokinetic dynamics.

Keywords: Induced charge electroosmosis, Electrokinetic ion transport, Polymer molecules, Viscoelastic fluids, Flow instability.