Functionalized glass coating for PDMS microfluidic devices

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Soft Matter Keywords

Wettability, Microfluidics


Microfluidic devices can perform multiple laboratory functions on a single, compact, and fully integrated chip. However, fabrication of microfluidic devices is difficult, and current methods, such as glass-etching or soft-lithography in PDMS, are either expensive or yield devices with poor chemical robustness. We introduce a simple method that combines the simple fabrication of PDMS with superior robustness and control of glass. We coat PDMS channels with a functionalized glass layer. The glass coating greatly increases the chemical robustness of the PDMS devices. As a demonstration, we produce emulsions in coated channels using organic solvents. The glass coating also enables surface properties to be spatially controlled. As a demonstration of this control, we spatially pattern the wettability of coated PDMS channels and use the devices to produce double emulsions with fluorocarbon oil.

Soft Matters

The authors here demonstrate a method to to treat PDMS microfluidic devices with photoreactive glass coatings with the ability to spatially control wetability.

To make the chemically resistant glass coating the authors:

  • mix equal volumes of:
    • Tetraethoxysilane (TEOS) (Sigma)
    • Methyltriethoxysilane (MTES) (Sigma)
    • Hydrochloric acid aqueous pH 2
    • Ethanol (Sigma)
  • Flow mixture into PDMS device that has been recently bonded via plasma treating
  • Heat at 100C for 10s, flush with air then heat while continually flushing with air.

Photoreactive sol-gel coating

  • Mix photoiniator silane using:
    • Irgacure 2959 photoinitiator (Ciba)
    • Hydroquinone (Sigma)
    • Dibutyltin dilaurate (Sigma)
    • Dry chloroform (Sigma)
    • 3-(triethoxysily)propyl isocyanate (Sigma)
  • Use photoiniator to make sol-gel coating
    • Dissolve 0.5g of photoiniator-silane in 2mL of
    • Add 1mL Methyltriethoxysilane, 1mL Tetraethoxysilane, Trifluoroethanol and 0.5mL Heptadecafluoro-1,1,2,2- tetrahydrodecyl)triethoxysilane
    • Add 1mL pH 2 HCL and mix at 200C
  • Fill freshly bonded device (plasma) with sol-gel coating and wait for 2 min.
  • Place on 220C hotplate to vaporize solvent and deposit coating onto channel walls.

Spatially pattern hydrophillic areas

  • Mix hydrophillic monomer solution
    • Add 0.2mL of acrylic acid to 0.8mL of 5mM NaIO4, 1mL ethanol and 0.05g benzophenone in 0.5mL acetone.
  • Fill channels with monomer
  • Illuminate desired areas with diaphragm of Kohler illuminated microscope
  • Photopolymerize desired areas by exposing to UV light for 2-10 mins (time inversely proportional to channel size
  • Flush with water

From SEM images of treated and untreated PDMS, the sol-gel coating is roughly 5<math>\mu m</math>.

SEM image of native pdms and sol-gel coated PDMS.

The sol-gel coating makes the channels hydrophobic, which is useful for fabricating devices that make water in oil droplets while the hydrophillic monomer coating is useful for oil in water emulsion devices. Combined with the spatial patterning, the authors demonstrate the ability to fabricate monodisperse multiple emulsion droplets.