Tamara Floyd-Smith

Compressed-air flow control system

We present the construction and operation of a compressed-air driven flow system that can be used for a variety of microfluidic applications that require rapid dynamic response and precise control of multiple inlet streams. With the use of inexpensive and readily available parts, we describe how to assemble this versatile control system and further explore its utility in continuous- and pulsed-flow microfluidic procedures for the synthesis and analysis of microparticles.

Feasibility Assessment of the Integration of Microfluidics and NEPCM for Cooling Microelectronics Systems

The growing demand for microelectronic systems to be smaller and faster has increased the energy released by these devices in the form of heat. Microelectronic systems such as laptop computers and hand held devices are not exempted from these demands. The primary traditional technologies currently used to remove heat generated in these devices are fins and fans. In this study, traditional methods were compared to more novel methods like cooling using forced convection in microfluidic channels and stagnant nanoparticle enhanced phase change materials (NEPCM). For this study, the difference between the surface temperature of a simulated microelectronic system without any cooling and with a particular cooling method was compared for several cooling scenarios. Higher ΔT values indicate more effective cooling. The average ΔT values for fans, fins, NEPCM and microchannels with water were 2°C, 5°C, 3°C and 4°C respectively. These results suggest that, separately, microchannel cooling and NEPCM are promising methods for managing heat in microelectronic systems.Even more interesting than NEPCM or microchannel cooling alone is the potential cooling that can be achieved by combining the two methods to achieve multimode cooling first by the phase change of the NEPCM and then by circulating the nanofluid (melted NEPCM) through microchannels. A feasibility assessment, however, reveals that the combination of the two methods is not equal to the sum of the parts due to the viscosity and associated pumping power requirements for the melted phase change material. Nonetheless, the combination of the method still holds promise as a competitive alternative to existing thermal management solutions.Copyright

RHEOLOGICAL CHARACTERIZATION OF NON-NEWTONIAN FLUIDS WITH A NOVEL VISCOMETER

A hydrostatic head viscometer and its novel viscosity equation were developed to determine flow characteristics of Newtonian and non-Newtonian fluids. The objective of this research is to test capabilities of the hydrostatic head viscometer and its novel non-Newtonian viscosity equation by characterizing rheological behaviors of well-known polyethylene oxide aqueous solutions as non-Newtonian fluids with 60 wt.% sucrose aqueous solution as a reference/calibration fluid. Non-Newtonian characteristics of 0.3–0.7 wt.% polyethylene oxide aqueous solutions were extensively investigated with the hydrostatic head viscometer and its non-Newtonian viscosity equation over a 294–306 K temperature range, a 0.14–40 Reynolds number range, and a 55–784 s−1 shear rate range at atmospheric pressure. Dynamic viscosity values of 60 wt.% sucrose aqueous solution were determined with the calibrated hydrostatic head viscometer and its Newtonian viscosity equation over a 3–5 Reynolds number range at 299.15 K and atmospheric pressure and compared with the literature dynamic viscosity value.

Stop flow lithography synthesis and characterization of structured microparticles

In this study, the synthesis of nonspherical composite particles of poly(ethylene glycol) diacrylate (PEG-DA)/SiO2 and PEGDA/ Al2O3 with single or multiple vias and the corresponding inorganic particles of SiO2 and Al2O3 synthesized using the Stop Flow Lithography (SFL)method is reported. Precursor suspensions of PEG-DA, 2-hydroxy-2-methylpropiophenone, and SiO2 or Al2O3 nanoparticles were prepared. The precursor suspension flows through a microfluidic device mounted on an upright microscope and is polymerized in an automated process. A patterned photomask with transparent geometric features masks UV light to synthesize the particles. Composite particles with vias were synthesized and corresponding inorganic SiO2 and Al2O3 particles were obtained through polymer burn-off and sintering of the composites. The synthesis of porous inorganic particles of SiO2 and Al2O3 with vias and overall dimensions in the range of ∼35-90 µm was achieved. BET specific surface area measurements for single via inorganic particles were 56-69m2/g for SiO2 particles and 73-81m2/g for Al2O3 particles. Surface areas as high as 114m2/g were measured formultivia cubic SiO2 particles. The findings suggest that, with optimization, the particles should have applications in areas where high surface area is important such as catalysis and sieving.

Microfluidics for Controlled Production of Thin Films and Particles

Tailored materials with nano to micron dimensions are becoming increasingly important for niche applications in optics, personnel protection and biomedicine. Microfluidics is a robust platform for producing these tailored materials because of the spatial control that can be realized in microfluidic systems due to laminar flow profiles and small dimensions. For this work, a pre-polymer solution, consisting of water, polyethylene glycol diacrylate (PEGDA) and a photo-initiator, flows through a microfluidic channel. For the general scheme, the pre-polymer is exposed to UV light in the microfluidic channel to crosslink the polymer. Depending on the application, the model pre-polymer, PEGDA, may need to be substituted with a different photo-polymerizable pre-polymer to address issues such as chemical compatibility and moisture stability prior to commercialization. Nonetheless, proof-of-concept is demonstrated using PEGDA with results that are transferrable to other photo-polymerizable pre-polymers.For this work, two distinct applications will be presented. In one application, the pre-polymer has a graded profile of nanoparticles. The nanoparticles modify the refractive index of the heterogeneous material and allow light to be directed through the material according to Snell’s Law. When the pre-polymer solution is polymerized, a thin film with a controlled refractive index profile is produced with potential for waveguiding applications. In a second application, the light is masked during UV exposure to produce particles instead of thin films. The particles can be of any two-dimensional extruded shape. If the pre-polymer solution is loaded with ceramic nanoparticles and sintered, ceramic particles that retain the shape of the original composite particle are produced. To date, numerous particle cross sections of polymeric particles and limited ceramic particles have been demonstrated with applications in liquid body armor, abrasives and drug delivery.Copyright