[CCoE Notice] Thesis Defense: Investigation of Dielectrophoresis-Directed Fluidic Assembly

[Thayer, Natalie H]

INVESTIGATION OF DIELECTROPHORESIS-DIRECTED FLUIDIC ASSEMBLY

Guoliang He

July 23rd 2015
ME Large Conference Room
10:00 AM

Committee Chair:      Dr. Dong Liu
Committee Members:
Dr. Tsorgn-Whay Pan
Dr. Matthew Franchek
Dr. Anastassios Mavrokefalos
Dr. Cunjiang Yu


Dielectrophoretic fluidic self-assembly of nanoscale building blocks, such as nanoparticles and nanowires, by various external means is a promising alternative to the current microfabrication techniques to manufacture functional microdevices.  While individual particle can be manipulated with reasonable precision, it remains a grand challenge to scale up the assembly process to reproducibly assemble a large number of particles. This is partially due to the lack of a quantitative understanding of the complex fluid-particle dynamics when numerous nanostructures are interacting both electrically and hydrodynamically.  In this work, both experiment and numerical study were conducted to explore the electrokinetic effect during the assembly of multiple nanostructures, especially spherical particles, driven by dielectrophoresis (DEP) in microfluidic channels.

The direct numerical simulations are conducted as a combination of Maxwell Stress Tensor and Distributed Lagrange Multiplier / Fictitious Domain methods for particles self-assembly in an external electric field.  The DEP forces and torques exerted on the particles are computed using the Maxwell stress tensor (MST) approach.  Unlike the commonly used effective dipole approach and the multipolar moment approach, MST is able to yield rigor solutions of the DEP force/torque even when the particles are in the vicinity of the electrodes.  The particle-fluid interactions are modeled using the distributed Lagrange-multiplier based fictitious-domain (DLM/FD) method.  The motion of the individual particle and the subsequent aggregation of adjacent particles are studied in details.  Analytical solutions, if available, are used to validate of the numerical model and as a guideline for experiments.  Experiments are conducted for colloidal particles on microfabricated devices.  The motion of the particles is observed under a microscope with UV light focusing on the colloidal region. It is recorded by a camera connected to a computer.  The positions of the particles are tracked and analyzed by Matlab based on experiment images, from which the initial positions are used in numerical simulation for comparison.  The numerical simulation shows good agreement with the experiment in terms of patterns and trajectories.

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