Concentration-polarization electroosmosis: Full numerical simulation and comparison with the thin double layer model

We present a comprehensive numerical study of concentration-polarization electroosmosis (CPEO) around a charged spherical particle subjected to an alternating current electric field. The analysis is based on the full solution of the coupled Poisson–Nernst–Planck and Stokes equations, allowing us to assess the validity of commonly used theoretical approximations. In particular, we compare the full numerical results with the macroscale electrokinetic model of Schnitzer and Yariv (SY), which relies on the thin electrical double layer (EDL) assumption and is widely used to describe nonlinear electrokinetic phenomena. Our simulations are first validated against classical results for electrophoretic mobility, showing excellent agreement. We then investigate CPEO flows over a wide range of parameters, including electric field strength, frequency, zeta potential, and EDL thickness. For thin EDLs and sufficiently large zeta potentials, the SY model provides accurate predictions of both the flow structure and magnitude. However, significant deviations arise as the zeta potential decreases or as the EDL thickness increases. In the regime of thick EDLs, we observe qualitative changes in the flow, including a reversal of the quadrupolar pattern. Finally, we compare our numerical predictions with available experimental data, finding overall good agreement but also highlighting discrepancies at high electric field strengths, where the experimentally observed saturation of the flow is not captured by current models.