Development of a Hybrid Numerical Model for Dielectrophoretic Particle Assembly in Microfluidic Device

Mohammad Robiul Hossan

Dielectrophoresis, a nonlinear electrokinetic transport mechanism, becomes popular in many engineering and biomedical applications for manipulation, characterization and actuation of biomaterials, particles and biological cells. However, the underlying fundamental mechanism of dielectrophoresis has not been fully understood yet due to the complexity of transient micro/nanoscale physics. These phenomena become more complex with an increase in the number of interacting particles. The dynamics of dielectrophoresis has been studied using different approximate approach such as point dipole and Stokes drag approximation. However, these approximations produce erroneous results if particles are near to the electrode or another particle, the electric field is highly nonuniform, particle and device size are comparable; and approximate methods ignore particle dynamics and particle-particle interactions. To overcome the limitations of the existing methods and eliminate different approximations, a hybrid immersed interface-immersed boundary method has been developed for modeling and simulation of dielectrophoresis. An efficient algorithm is developed to obtain alternating electric potential distribution with suspended particles without dealing complex variables in computation for AC dielectrophoresis. The immersed interface method is employed to obtain electric field in a fluid media with suspended particles where immersed boundary method is used to study hydrodynamic interaction in particle transport. Dielectrophoretic (DEP) force distributions are obtained using Maxwell's stress tensor. After validation and grid refinement analysis, the superiority of the developed model has been demonstrated by comparing with point dipole approximation for calculating DEP forces. Then the method is used to elucidate physics behind dielectrophoresis, design and study of DEP particle trap and analyze DEP particle assembly and particle-particle interactions. Numerical results show that in a fluid media, similar and electrically dissimilar particles form distinct assembly under an external electric field. The results also show that with proper design of microdevice, the global electric field minima can be obtained to facilitate particle trapping by exploiting negative dielectrophoresis. Finally, this hybrid scheme is extended for modeling and simulation of bipolar ellipsoidal particles and studied bipolar particle dynamics, self and electric field guided orientation mechanism.

Development of a Hybrid Numerical Model for Dielectrophoretic Particle Assembly in Microfluidic Device

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