Date of Award

Spring 1-1-2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical & Biochemical Engineering

First Advisor

Robert H. Davis

Second Advisor

Christopher N. Bowman

Third Advisor

Alexander Zinchenko

Fourth Advisor

Christine M. Hrenya

Fifth Advisor

Patrick D. Weidman

Abstract

Microfluidic devices have significant potential for use in the separation and isolation of particulates, based on their chemical or physical properties. Implementation of microfluidic devices in the separation of biological components has dramatic potential advantages; however, those advantages are accompanied by equally difficult challenges relating to fabrication, consistency, robustness, and reliability of the device. One technique used to achieve particulate separations employing a microfluidic device based on the size of the particles is pinched-flow fractionation (PFF). PFF provides a simple, efficient methodology for size-based particle separation using fluid mechanics principles.

We developed techniques for constructing microfluidic devices having high- aspect-ratio features, quality and fidelity. In this work, a modified, confocal- microscopy technique was developed to quantitatively determine feature quality. Microfluidic devices and independent, photolithographically-defined features were constructed using thiol-ene resins by means of a soft-lithography technique; contact liquid photolithographic polymerization (CLiPP). Resin cure times and initiator-to-inhibitor ratio were found to have a strong impact on feature quality. A correlation between aspect ratio and feature thickness for thiol-enes was established, as well. Combining the optimization technique with thiol-ene materials led to the formulation of a photopolymerizable resin capable of fabricating high quality, high-aspect-ratio microfluidic channels that were used to fabricate a PFF device.

The final aim of this dissertation was to utilize moving-frame boundary-Integral method (MFBIM) developed in this work to assist in the design of a microfluidic device with enhanced separation efficiency. Previous studies of PFF devices have shown that channel geometry, flow rate and particle size all affect particle trajectories, and hence, separation efficiency. To study the effects of channel geometry, particle size, and fluid flow on the PFF device’s separation performance, a microfluidic channel using the PFF geometry was fabricated. Simulations using the MFBIM were conducted to predict the effects of channel geometry, flow rates, and particle sizes on separation efficiency. The MFBIM simulations provided a method used to predict particle trajectories while varying the flow ratio, particle size and channel geometry. Data from the simulations were used to design a PFF device with optimal separation attributes by modifying the channel geometry and flow ratio.

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