Electrokinetic Separation of Microplastics Using a Hybrid Dielectrophoresis-Bipolar Electrode Microchannel

The environmental persistence of microplastic particles has raised increasing concerns for both human health and ecological systems. Owing to their intrinsic electrical properties and broad size distribution, electrokinetic-based microfluidic separation techniques have attracted increasing attention. In this study, a hybrid dielectrophoresis-bipolar electrode (DEP-BPE) microchannel is proposed to enhance particle separation across multiple size scales. A multiphysics numerical model coupled with particle tracking is developed to investigate the coupled electrokinetic mechanisms governing particle transport, including dielectrophoretic (DEP) force, electrophoretic migration, and electroosmotic flow (EOF)-induced hydrodynamic drag. The results show that increasing the applied voltage amplifies electrokinetic forces and significantly improves removal efficiency. However, the separation performance exhibits a non-monotonic dependence on voltage, arising from the competition between lateral DEP displacement and axial transport driven by electrophoresis and EOF. An optimal voltage condition is identified, under which trajectory differentiation is maximized without over deflection. Electrode spacing is found to primarily regulate the spatial distribution of electrokinetic interactions, exerting a limited influence on overall separation strength but significantly affecting the location of particle deflection and trajectory evolution. These findings demonstrate that particle separation in the DEP-BPE microchannel is governed by the coupling between force magnitude and spatial distribution and highlight the effectiveness of integrating DEP-induced stratification with BPE-driven trajectory divergence. This work provides mechanistic insights and design guidelines for high-efficiency microfluidic separation of polydisperse microplastic particles.