A Novel Fabrication Method To Integrate Super Hydrophobic Nano Structures Into Microfluidic Devices

1
A Novel Fabrication Method To Integrate Super
Hydrophobic Nano Structures Into Microfluidic
Devices

• Laura Zimmermann, Markus Guttmann, Andreas Guber,
  Volker Saile

2
Content

• Motivation
• Simulation results
• Fabrication process
• Experimental results
• Conclusions

3
Motivation

• Encapsulation of biological/ chemical substances
  requires generation of discrete droplets with
• periodic droplet break up
• droplets with constant volume
• Droplet based microfluidic systems with nano
  structured surface topography having super
  hydrophobic properties
• Fabrication process developed to create
  microfluidic devices with 3D nano structured
  channel walls.

4
Simulation results unmodified channel surfaces

• Comsol Multiphysics
• level set method
• boundary conditions
• liquid two phase system
• channel dimensions 100 µm
• contact angle of channel surface 74
• flow rate ratio 10080 µl/min
• droplet break up
• irregular
• with non uniform volume
• for channel surfaces with contact angles below
  90.

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Simulation resultssurface modified channels

• Comsol Multiphysics
• level set method
• boundary conditions
• liquid two phase system
• channel dimensions 100 µm
• contact angle of channel surface 120
• flow rate ratio 10080 µl/min
• droplet break up
• periodic
• with constant volume
• if surfaces of the channel walls have
  contact angles higher than 120.

6
Fabrication process for 3D nanostructured
microfluidic devices
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Electron beam lithography and electroforming

• structuring of resist (height 300nm) by
  electron beam lithography
• pattern consists of pillars in a hexagonal manner
  (Ø 200nm, pitch 400nm, height 300nm) on a
  surface area of 4 inches
• developping of resist
• sputtering of conductive layer for electroplating
• nickel electroforming (thickness 500µm)
• KOH etching of silicon substrate
• stripping of remaining resist

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Hot embossing

• nickel shim and thermoplastic polymer foil are
  placed in hot embossing machine
• evacuation of setup
• whole setup heated above glass transition
  temperature of thermoplastic polymer
• application of force
• cooling while force is kept constant
• demoulding

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Super hydrophobic polymer foils

• all thermoplastic polymers can be processed
• low cost fabrication of super hydrophobic
  polymers
• further processing possible
• polymer foils up to 4 inches can be embossed

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Thermoforming

• nano structured polymer foil and thermoforming
  mask with microfluidic channel system are placed
  in thermoforming machine
• setup heated 10-20C below glass transition
  temperature
• gas pressure applied
• nano structured foil stretched into microfluidic
  channel system mask
• cooling started while gas pressure is kept
  constant
• gas pressure decreased when demoulding
  temperature is reached

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ExperimentsSetup

• assembly
• two polymer foils welded
• connected to PTFE tubings
• experimental setup
• syringe pump
• camera
• microscope
• PC
• droplet analysing software

12
Unmodified microfluidic device

• experiments verify simulation results
• droplet break up is
• irregular
• with non uniform volume.

50
13
Surface modified microfluidic devices

• experiments verify simulation results
• droplet break up is
• regular
• with uniform volume.

10
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Conclusions

• microfluidic devices based on polymers
• fabrication process for nano structured shim
  inserts and polymer devices
• fabrication of spherical channel walls with 3D
  nano structured surface
• super hydrophobic surface properties all over the
  channel surface
• flexible design of microfluidic systems
• low cost fabrication of microfluidic devices
• droplet generation is periodic and with constant
  volumes
• application
• encapsulation of single cells
• encapsulation of chemical substances

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• Thank you very much for your attention!
• Acknowledgment
• P. Jakobs
• A. Bacher
• H. Hellriegel
• J. Barth
• M. Worgull