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