Date of Award

8-2016

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Mechanical Engineering

Committee Member

Dr. Xiangchun Xuan, Committee Chair

Committee Member

Dr. Lonny Thompson

Committee Member

Dr. Rodrigo Martinez-Duarte

Abstract

Electrokinetically-driven deterministic lateral displacement (e-DLD) is a recently proposed technique for continuous, two-dimensional fractionation of particle suspensions in microfluidic platforms. It utilizes the negative dielectrophoretic force that is induced by the DC electric field gradients formed around an array of regularly spaced posts. While e-DLD devices have been demonstrated to be able to separate particles by size, a fundamental understanding of the separation process and the factors that affect the separation is still lacking. This thesis is aimed to answer these questions using a computational study of electrokinetic particle transport and separation in e-DLD devices. We first numerically prove a continuous, two-dimensional separation of 5 μm, 10 μm and 15 μm-diameter rigid circular particles in an e-DLD device. These particles can be viewed as good mimics of red blood cells, white blood cells and tumor cells, respectively, in blood. A number of features are observed in the kinetics of particles, including directional locking and sharp transitions between migration angles upon variations in the direction of the force, which are advantageous for high-resolution two-dimensional separation.We then discuss several factors that affect the separation of particles in the proposed e-DLD device, such as electric field, forcing angle, post gap ratio, post shape and particle shape. We find that the electric field influences the particle separation by affecting the electric field gradient. The larger electric field, the larger electric field gradient will be. We also investigate the orientation of the driving field with respect to the array of posts and find that, at specific forcing-angles, particles of different sizes migrate in different directions, enabling continuous, two-dimensional separation in electrokinetic flow. Moreover, we study the effect of the post gap ratio on particle separation. The smaller the ratio, the larger the electric field gradient will be around the posts, so particles will more easily get deflected away from the posts due to the enhanced negative dielectrophoretic force. In addition, we find that the shape of posts plays an important role in particle separation. Using equilateral triangular posts, we are able to separate smaller particles as compared to the traditional circular posts under the same conditions. We also look into the effect of particle shape on separation in e-DLD. It is found that an elliptic particle behaves like a smaller sized circular particle due to its preferred orientation in electric field. Therefore, we can easily achieve the separation of circular and elliptic particles with an equal surface area. In the end, we compare e-DLD with the traditional pressure-driven DLD. With the same geometry, e-DLD device is capable of separating much smaller particles. Alternatively, pressure-driven DLD requires a smaller gap size and/or a smaller forcing angle to implement the same particle separation which will make the manufacture harder. Using e-DLD device will considerably ease the DLD device fabrication and shorten the length of the post array.

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