Applications of the boundary-element method for electrokinetics in microfluidics
House, Dustin L
The use of electric fields to control colloids has proven to be a promising form of actuation for microfluidic devices. However, limiting our ability to exert precise control over colloidal samples using this technique is a lack of understanding of the complex situations of closely-bounded flow and non-spherical particle interaction. Considering the size and shape of biological particles and the size restraints of the channels in which they are contained, these situations are typically unavoidable. For these situations, exact solutions are often unavailable and finite-element methods can be inaccurate and inefficient for the highly distorted electric fields in narrow gap regions. To investigate these electrokinetic scenarios, we develop a boundary-element method (BEM). By reducing the dimension of the computational domain and utilizing quadrature integration, this technique is more efficient and can be much more accurate than volume meshes used by finite-element approaches. After linearizing the governing equations, the BEM is able elucidate the complex interaction among particle, electric field and flow field that is otherwise neglected by other commonly used approximations. We believe the BEM can be an efficient tool for microchannel design and optimization. Thus, the goal of this research is to advance its application within electrokinetics in microfluidics. This is done by developing a 2D and 3D code to simulate particle motion in the presence of electrophoresis, electroosmosis and dielectrophoresis. Three specific problems are considered. First, we model an electrophoretic particle bounded by two parallel walls. In this study, we find that for a tightly-bound particle, the viscous drag is comparable to its electrophoretic effect. Next, we model a particle traveling through a bent pore subject to a dielectrophoretic force. Here, we conclude that the particle's size has an increasingly significant effect on its lateral migration, especially when positioned close to the wall. The third application concerns the dielectrophoretic interaction of two slender particles and formation of particle chains. The two particles are found to realign themselves and then come together, forming a chaining pattern consistent to previous experimental observation.