Electrophoresis of Colloidal Particles Coated with Charged Hydrogel: Nonlinear Electrokinetic Effects and Thermal...

Electrophoresis is a fundamental electrokinetic process used to study the motion of charged particles under an applied electric field, with applications in colloidal science, biomedical diagnostics, and environmental systems. Classical electrophoretic theories, such as the Smoluchowski and Hückel models, assume rigid particles with thin double layers and uniform surface charge, which are inadequate for soft colloidal systems like hydrogel-coated or polyelectrolyte-layer (PEL) particles. In such systems, ion penetration, porous structures, and nonlinear electrokinetic interactions significantly influence particle mobility. This study develops a nonlinear electrokinetic framework for hydrogel-coated colloidal particles by incorporating double-layer polarization, ion steric effects, ion partitioning, and Joule heating-induced thermal coupling. The governing Navier-Stokes, Nernst-Planck, Poisson, and energy equations are solved using a combined analytical perturbation approach and a finite volume-based computational fluid dynamics method. Quantitative results show that mobility increases from 1.02 × 10^-8 to 7.60 × 10^-8 m²/(V s) as zeta potential rises from 10 to 100 mV, while nonlinear polarization reduces mobility by 24-27% compared to classical predictions. Steric effects cause up to 40% reduction, and PEL structural variations produce mobility differences of up to 55%. Thermal coupling raises mobility from 4.2 to 7.1 × 10^-8 m²/(V s) between 298 and 338 K, a 69% increase. Model predictions agree with experimental data within 4% error, demonstrating improved accuracy for soft colloidal systems.