Actuation of Pico-Liter Drops by Stick-Slip Motion
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Actuation of Pico-Liter Drops by Stick-Slip Motion
Devon PowellDr. Peter Bennett, MentorASU Physics Department
Arizona Space Grant 2010 Statewide Symposium
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Background• Microfluidic devices for processing discrete volumes require
manipulation of liquid drops on a surface.• Applications:
– Molecular biology– DNA analysis– Proteomics– Clinical pathology
• Some existing methods:– Electrowetting– Dielectrophoresis– Ratcheting on asymmetric
surfaceshttp://cores.montana.edu/uploads/images/misc/Fxnl%20Genomics%20Core%20Facility/microfluidics.jpg
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Objective
• Translate nano- to pico-liter droplets– Stick-slip– Asymmetric (i.e., sawtooth)
vibration • Operating Principles:
– Difference between static and kinetic “friction”
– Contact angle hysteresis– Droplet resonance
• Flexibility due to real-time control
Slow, droplet sticks
Fast, droplet slips
Net displacement
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Achievements To Date• Apparatus
Construction• Surface Treatments• Initial contact angle
measurements– Contact angle
hysteresis• Verified resonant
behavior in large water droplets– Daniel et al.
Me Working - Picture Here
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Apparatus
• Viewing chamber– Magnetic mount,
mechanical in future• Piezo system• Camera, LCD strobe• New scope
modification– CCD camera– Long distance objective
Lab Photo
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Lab Photo
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Surfaces/Sessile Contact Angle
• HF-dipped silicon– Good hydrophobicity– Poor persistence
• Treated glass– OTS– ~106°
• Future:– Silanized silicon– Mercury on glass
Lab Photo
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Contact Angle Hysteresis
• Poor CAH data– α = 37-62°– Assume uniform contact
line– Need better surface
condition• Dynamic measurement– Substrate tracking
Lab Photo
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Resonance• Mass-spring analogy– Inertia m– Restorative force kx
• For droplets,
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Resonance
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Thank You