Ms. Connie E. Drewbrook Profile

Connie E. Drewbrook

at Simon Fraser Univ

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Publications (2)

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Proceedings Article | 16 February 2011 Paper

Large scale micropatterning of multi-walled carbon nanotube/polydimethylsiloxane nanocomposite polymer on highly flexible 12x24 inch substrates

A. Khosla, D. Hilbich, C. Drewbrook, D. Chung, B. Gray

Proceedings Volume 7926, 79260L (2011) https://doi.org/10.1117/12.876738

KEYWORDS: Nanocomposites, Polymers, Polymethylmethacrylate, Laser systems engineering, Carbon dioxide lasers, Electrodes, Microfabrication, Carbon, Carbon nanotubes, Ultrasonics

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We present the large scale micro-pattering of an electrically conducting multiwalled carbon nanotube (MWCNT) polydimethylsiloxane (PDMS) nanocomposite polymer prepared by high frequency (42 kHz) ultrasonic agitation of MWCNTs in the PDMS polymer matrix. Large scale micropatterning of the MWCNT-PDMS nanocomposite is achieved via soft lithography employing a 12" × 24" poly-methyl methacrylate (PMMA, commercially known as Plexiglass) micromold. The process has a 20µm minimum feature size. The PMMA micromold is fabricated by laser ablating 5-mm thick, 12" × 24" sheets using the Universal Laser System's VersaLASER© laser cutter system which employs a CO₂ laser. We have characterized and compared the resistivity of 1cm × 0.5cm × 0.5cm MWCNT-PDMS structures with varying weight percentage (wt-%) of MWCNT (1-10% wt%) in the PDMS matrix with a result that the percolation threshold is achieved at 2 wt-%. Furthermore, we have demonstrated the ability to fabricate large numbers of microelectrodes with a length of 3.0 cm, width of 500µm, and height of 400µm. The resistivity of these electrodes was found to be equal to 9.93Ωm with a deviation of approximately 10%, indicating uniformity across large areas of the substrate. We have also demonstrated a large scale 12" × 24 hybrid microfabrication process for combining micromolded MWCNT-PDMS nanocomposite microstructures with nonconductive PDMS polymer.

Proceedings Article | 15 February 2011 Paper

Fabrication and testing of thermally responsive hydrogel-based actuators using polymer heater elements for flexible microvalves

Ang Li, Ajit Khosla, Connie Drewbrook, Bonnie Gray

Proceedings Volume 7929, 79290G (2011) https://doi.org/10.1117/12.873197

KEYWORDS: Actuators, Polymers, Microfluidics, Polymeric actuators, Nanocomposites, Microactuators, Tungsten, Nanoparticles, Silicon, Polymerization

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We present the design, fabrication and characterization of a mechanically flexible diaphragm-based microvalve actuator employing a reservoir of the thermally responsive hydrogel PNIPAAm and a conductive nanocomposite polymer (C-NCP) heater element. The microvalve actuator can be fabricated employing traditional soft lithography processes for fabrication of all components, including the tungsten-based C-NCP heater element, the hydrogel reservoir, and the deflecting polymer membrane. Shrinking of the hydrogel under the application of heat supplied by the flexible heater, or the removal of this thermal energy by turning off the heater, forces the diaphragm to move. The silicone diaphragm actuator is compatible with a normally-closed polymer microvalve design where-by the fluidic channel can be opened and closed via the hydrogel diaphragm actuator, in which the hydrogel is normally swollen and heating opens the valve via membrane deflection. Our prototype hydrogel actuator diaphragms are between 100-200 micrometers in diameter, and experimentally deflect approximately 100 micrometers under heating to 32 degrees ºC or above, which is sufficient to theoretically open a microvalve to allow flow to pass through a 100 micrometer deep channel. We characterize the flexible tungsten C-NCP heaters for voltage versus temperature and show that the flexible heaters can reach the hydrogel transition temperature of 32 degrees °C at approximately 13-15 V. We further characterize the hydrogel response to heat, and diaphragm deflection using both hot plate and flexible C-NCP heater elements. While our results show diaphragm deflection adequate for microvalves at a reasonable voltage, the speed of deflection is currently very slow and would result in slow microvalve response speed (30 seconds to open the valve, and 120 seconds to reclose it).

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