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electrowetting-driven digital microfluidic devices

electrowetting-driven digital microfluidic devices. Frieder Mugele University of Twente Physics of Complex Fluids. Fahong Li, Adrian Staicu, Florent Malloggi, Rina Bakker, Jean-Christophe Baret. EW for droplet-based digital microfluidics. detachment / drop generation. droplet motion.

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electrowetting-driven digital microfluidic devices

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  1. electrowetting-drivendigital microfluidic devices Frieder Mugele University of Twente Physics of Complex Fluids Fahong Li, Adrian Staicu, Florent Malloggi, Rina Bakker, Jean-Christophe Baret

  2. EW for droplet-based digital microfluidics detachment / drop generation droplet motion drop merging mixing surface contamination

  3. outline • wetting & electrowetting – some basics • principles of drop actuation • basics of EW-modeling • application-related fundamental issues • mixing in microfluidics • surface protection • conclusions & wish list

  4. I: wetting & liquid microdroplets 50 µm capillary equation Young equation H. Gau et al. Science 1999

  5. electrowetting: the switch on the wettability low voltage: parabolic behavior electrowetting equation: high voltage: contact angle saturation advancing receding h conductive liquid insulator counter electrode U U

  6. II: origin of electrowetting + + + + + + + + + U Maxwell stress: ssleff modified capillary equation modified Young equation

  7. principles of drop actuation ~ how to make water run uphill with EW? U driving force:

  8. matrix chip 1mm matrix chip (10x10 electrode lines) ITO glass operating voltage: 70V @ 10kHz insulator: teflon AF

  9. characteristics drop volumes: 1nL … 1µL possilbe fluids: broad spectrum ( table)

  10. suitable liquids for EW D. Chatterjee et al., Lab on a Chip 2006

  11. characteristics drop volumes: 1nL … 1µL possilbe fluids: broad spectrum ( table) substrate materials: any insulator + hydrophobic top coating (typically: Teflon AF) actuation voltage: few tens of volts drop speed & switching speed: O(cm/s) & tens of Hz

  12. III: modelling EW-driven flow • fAC=10 kHz • fosc=17 Hz • glycerol + NaCl • solution in silicone oil 500 µm

  13. numerical calculations: volume of fluid experiment volume of fluid calculations fexp= 24 Hz fnum= 34 Hz µ=80mPa s attached state: q = 65° detached state: q = 155° principle: contact angle variation + hydrodynamic response caveat: contact line dynamics !

  14. IV a: EW-driven mixing in oscillating droplets salt water; fosc = 80 Hz; fAC= 10 kHz 500 µm flow visualization PIV measurements (J. Westerweel & Ralph Lindken TU Delft)  drop oscillations speed up mixing 100 times

  15. IV b: surface protection & oil entrapment V ≈ cm/s voltage time • µm thick oil layers are entrapped under moving drops • entrapped film undergo instability and break-up into droplets

  16. conclusions • electrowetting is driven by the gain in electrostatic energy upon reducing the contact angle and/or moving the drop • dynamics: local contact angle variation + hydrodynamic response • EW is very reliable, reproducible, and broadly applicable physical principles of EW are well understood EW review article • F. Mugele and J.-C. Baret • Electrowetting: from basics to applications • J. Phys. Condens. Matt. 17, R705-R774 (2005)

  17. issues to be fixed • droplet properties • desired drop volumes ( electrode size)? • liquid properties (conductivity, chemical composition, surfactants) • device characteristics • surface material requirements (Teflon AF) • AC – DC voltage • ambient medium: oil vs. air? • surface cleanliness / washing steps • reaction protocols • volume vs. surface-bound reactions • T-steps • detection techniques • optical measurements • integration of eletrical sensors (e.g. for conductivity)

  18. drop splitting CJ Kim et al.; UCLA numerical simulations using diffuse interface model (Cahn-Hilliard equation)

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