In this paper, we investigate the mechanism of two dimensional DC dielectrophoresis (DEP) using a hybrid immersed interface-immersed boundary method where both electric and hydrodynamic forces are obtained with interface-resolved approach instead of point-particle method. Immersed interface method is employed to predict DC electric field in a fluid media with suspended particles while immersed boundary method is used to study particle transport in a fluid media. The Maxwell stress tensor approach is adopted to obtain dielectrophoretic force. This hybrid numerical scheme demonstrates the underlying physics of positive and negative dielectrophoresis, and explains their contribution in particle assembly with consideration of size, initial configurations and electrical properties of particles as well as fluid media. The results show that the positive DEP provides accelerating motion while negative DEP provides decelerating motion depending on the electrode configurations and initial particle positions. The results also show that the local nonuniformity in electric field induced by the suspended particles guides the particles to form stable chain. Both positive and negative DEP can contribute in the process of particle assembly formation based on the properties of particles and fluid media. This hybrid immersed interface-immersed boundary scheme could be an efficient numerical tool for understanding fundamental mechanism of dielectrophoresis as well as designing and optimization of DEP based microfluidic devices.

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