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Comparison of monodisperse droplet generation in flow-focusing devices with hydrophilic and hydrophobic surfaces

Lab on a Chip

Roberts, Christine C.; Rao, Rekha R.; Loewenberg, Michael; Brooks, Carlton F.; Galambos, Paul; Grillet, Anne M.; Nemer, Martin N.

A thin flow-focusing microfluidic channel is evaluated for generating monodisperse liquid droplets. The microfluidic device is used in its native state, which is hydrophilic, or treated with OTS to make it hydrophobic. Having both hydrophilic and hydrophobic surfaces allows for creation of both oil-in-water and water-in-oil emulsions, facilitating a large parameter study of viscosity ratios (droplet fluid/continuous fluid) ranging from 0.05 to 96 and flow rate ratios (droplet fluid/continuous fluid) ranging from 0.01 to 2 in one geometry. The hydrophilic chip provides a partially-wetting surface (contact angle less than 90°) for the inner fluid. This surface, combined with the unusually thin channel height, promotes a flow regime where the inner fluid wets the top and bottom of the channel in the orifice and a stable jet is formed. Through confocal microscopy, this fluid stabilization is shown to be highly influenced by the contact angle of the liquids in the channel. Non-wetting jets undergo breakup and produce drops when the jet is comparable to or smaller than the channel thickness. In contrast, partially-wetting jets undergo breakup only when they are much smaller than the channel thickness. Drop sizes are found to scale with a modified capillary number based on the total flow rate regardless of wetting behavior. © The Royal Society of Chemistry.

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TYPE Journal Article YEAR 2012
ScopusOSTI

Packaging a liquid metal ESD with micro-scale mercury droplet

Galambos, Paul

Micro-Gas-Analyzers have many applications in detecting chemical compounds present in the air. MEMS valves are used to perform sampling of gasses, as they enable control of fluid flow at the micro level. Current generation electrostatically actuated MEMS valves were tested to determine their ability to hold off a given gauge pressure with an applied voltage. Current valve designs were able to hold off 98 psi with only 82 V applied to the valves. The valves were determined to be 1.83 times more efficient than older valve designs, due to increasing the electrostatic area of the valve and trapping oxide between polysilicon layers. Newer valve designs were also proposed and modeled using ANSYS multiphysics, which should be able to hold off 100 psi with only 29 V needed. This performance would be 2.82 times more efficient than current designs, or 5.17 times more efficient than older valve designs. This will be accomplished by further increasing the valve radius and decreasing the gap between the valve boss and electrode.

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TYPE SAND Report YEAR 2012
OSTIDOI

Packaging a liquid metal ESD with micro-scale Mercury droplet

Galambos, Paul

A liquid metal ESD is being developed to provide electrical switching at different acceleration levels. The metal will act as both proof mass and electric contact. Mercury is chosen to comply with operation parameters. There are many challenges surrounding the deposition and containment of micro scale mercury droplets. Novel methods of micro liquid transfer are developed to deliver controllable amounts of mercury to the appropriate channels in volumes under 1 uL. Issues of hermetic sealing and avoidance of mercury contamination are also addressed.

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TYPE SAND Report YEAR 2011
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Low leak rate MEMS valves for micro-gas-analyzer flow control

TRANSDUCERS 2009 - 15th International Conference on Solid-State Sensors, Actuators and Microsystems

Galambos, Paul; Lantz, J.W.; James, Conrad D.; McClain, Jaime L.; Baker, M.; Anderson, R.; Simonson, Robert J.

We present MEMS polysilicon microvalves for flow control of a rapid analytical microsystem (Micro-Gas-Analyzer, MGA). All valve components (boss, seat, springs, electrodes, and stops) are surface micromachined in the SUMMiT™ microfabrication process. The valves have been characterized at high flow rate when open (60 ml/min air), low leak rate when closed (<0.0025 ml/min Hydrogen, H2), and tunable closing pressures (1 to 35 psig). Active electrostatic valves have been shown to hold closed (voltage on) against a high pressure (>40 psig) for sample loading, open for gas chromatograph (GC) loading (voltage off), and reclose against low pressure 2-5 psig. ©2009 IEEE.

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TYPE Conference YEAR 2009
ScopusOSTI
Results 1–25 of 52
Results 1–25 of 52