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PDMS processing & devices

PDMS processing & devices. PDMS. PDMS. 1 st master. 3 rd substrate. active channel. control channel. PDMS. 2 nd master. PDMS. 2 nd master. Substrate: anything smooth and flat  silicon is the easy choice. Surface preparation: -bake  adsorbed water vapor out

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PDMS processing & devices

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  1. PDMS processing & devices

  2. PDMS PDMS 1st master 3rd substrate active channel control channel PDMS 2nd master

  3. PDMS 2nd master Substrate: anything smooth and flat  silicon is the easy choice Surface preparation: -bake  adsorbed water vapor out -clean: remove particles -adhesion promotion: HMDS

  4. Adhesion promotion HMDS More hydrophobic surface, Better adhesion with resist (which is organic polymer)

  5. Resist processing Resist dispensing Acceleration Final spinning 5000 rpm (a few milliliters) (resist expelled) (evaporation/partial drying)

  6. Resist processing Spin Bake (Align) Expose (Post exposure bake) Development Hard bake

  7. PDMS processing Pre-polymer and curing agent 10:1 ratio Mixing bubble free Casting Curing, e.g. 65oC, 2 h; or 40oC 10 h

  8. PDMS properties TgTdegr CTE Ther UV-transparency conduc 0C oCppm/oC W/K.m PMMA 100 200 70 0.2 opaque PC 150 230 65 0.2 >350 nm PDMS -130 400 300 0.15 >240 nm SU-8 240 340 100 0.2 >350 nm Polyimid400 620 3-50 0.2 opaque Parylene 150 290 35 0.1 >300 nm Teflon 130 330 100 0.1 opaque PDMS Young’s modulus 10 MPa very elastic, peels off easily

  9. Release Release criteria: -no retrograde angles -smooth surfaces -low surface energy -no interfacial reactions

  10. Masters • photolithography of SU-8 • photolithography and silicon etching • photolithography and metal electroplating • discharge machining • laser machining • mechanical milling • natural objects

  11. Masters (2) Why not silicon master ? Why not Teflon release layer ?

  12. PDMS 1st master Tg = glass transition temperature Above Tg polymer flows  hemispherical shape

  13. PDMS 3rd substrate Thin PDMS What is thin ? 10-50 µm Spin coating Applicable to viscous polymers Typical thickness: 1-100 µm Casting: 100 µm to mm’s

  14. PDMS 3rd substrate PDMS bonding Self-adhesive bonding ? Need strong bond for a valve application. Oxygen plasma activation Reactive OH-groups on surface  permanent bonding

  15. Valve closing

  16. Valve operation

  17. Flow switch

  18. Valve array Todd Thorsen, Sebastian J. Maerkl, Stephen R. Quake, Science 2002, Vol 298

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