David A. Baah, Ph.D. (2013)
Dissertation Topic: Microfluidic Synthesis of Non-Spherical Microparticles
Major Professor: Dr. Tamara Floyd-Smith, Professor of Chemical Engineering
MS: Chemistry, Tuskegee University
BS: Chemistry, Kwame Nkrumah University of Science and Technology, Ghana
Employment: Research Associate, Tuskegee University
The synthesis of non-spherical micron and nano-sized particles and their composites has been spurred by their application in select areas of optics, wear resistance, personnel protection, chemical mechanical polishing and biomedicine. Although the synthesis of highly monodisperse non-spherical particles with tunable functionalities has been a great challenge, microfluidics technology offers a unique opportunity towards the synthesis of these particles.
In this study, the synthesis of two-dimensionally extruded polymeric, polymer-nanoparticle composite, and ceramic non-spherical particles using Stop Flow Lithography (SFL) is described. Precursor suspensions of poly(ethylene glycol) diacrylate, 2-hydroxy-2-methylpropiophenone and SiO2 or Al2O3 are prepared. The precursor suspension flows through a microfluidic device mounted on an upright microscope and is polymerized in an automated process. A photomask patterned with transparent geometric features, that define the cross-sectional shapes of the particles, masks UV light to synthesize the particles. The particle axial dimension was controlled using three different channel depth devices (60-80, 100-150, and 220-250 µm), and the cross sectional area was controlled using a 10X or 20X magnification objective lens. A library of polymeric and composite particles with varying shape and size was synthesized. The corresponding inorganic SiO2 and Al2O3 particles were obtained through polymer burn-off and sintering of the composites.
This work is significant for several reasons. First, an automated SFL method was demonstrated in collaboration with the SFL pioneers. Next, the solvent-free, bulk collection of high fidelity polymeric particles was demonstrated, and the limits of the SFL method were explored. Lastly, for the first time, the SFL-assisted synthesis of Al2O3 microparticles was demonstrated thereby extending the applications of microfluidics particle synthesis to the area of abrasives.