Dielectrophoretic interaction of two particles in a uniform electric field

The local electric field distorsion induced by a dielectric particle leads to particle–particle interactions and assembly which is very interesting for their useful applications on microfluidic devices. Particles behavior becomes more complicated if several particles interact at the same time. This paper presents a comprehensive numerical analysis of the assembly and particle–particle interactions for two similar and dissimilar dielectric particles immersed in a dielectric fluid using the immersed interface method based on two-dimensional direct-current dielectrophoresis. The immersed interface method is a finite-difference (or finite element) based numerical method which its key advantage is implementing internal electrostatic boundary conditions over particles surfaces using a uniform mesh. This helps to better study the effect of electromagnetic fields on particles. When a single particle exposed to a uniform electric field, electric stresses are induced over its surface symmetrically. So the particle experiences no resultant DEP force. But if two particles are close enough to each other in an electric field, the electric stress distribution over each particle surface is not symmetric anymore. So there will be a resultant DEP interaction force between particles which makes them attract or repulse each other, depending on dielectric properties of buffer fluid and particles and their orientation with respect to electric field lines, as well. The effect of a nearby particle on electric stress distribution over the other particle is investigated in the present study to better explain the physics of particles DEP interaction. Also it is shown that by decreasing the distance between particles, the electric field gradient on particles becomes more intense. Numerical results show that in a dielectric medium, regardless of their initial position and orientation, two similar and dissimilar particles tend to form a parallel and perpendicular chain with respect to the applied electric field lines, respectively. Interaction and assembly of multiple particle chains in experiment observation can be explained by this numerical study.