1. PDMS processing & devices

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

3. 2 nd master PDMS 1.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. 65 o C, 2 h; or 40 o C 10 h

8. PDMS properties T g T degr CTETherUV-transparency conduc 0 C o Cppm/ o CW/K. m PMMA100200700.2opaque PC150230650.2>350 nm PDMS-1304003000.15>240 nm SU-82403401000.2>350 nm Polyimid4006203-500.2opaque Parylene150290350.1>300 nm Teflon1303301000.1opaque 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) 1.Why not silicon master ? 2.Why not Teflon release layer ?

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

13. PDMS 3 rd 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 3 rd 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

18. Flow switch

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