PDMS processing & devices

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

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

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

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

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

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

PDMS properties T g T degr CTETherUV-transparency conduc 0 C o Cppm/ o CW/K. m PMMA opaque PC >350 nm PDMS >240 nm SU >350 nm Polyimid opaque Parylene >300 nm Teflon opaque PDMS Young’s modulus 10 MPa  very elastic, peels off easily

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

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

Masters (2) 1.Why not silicon master ? 2.Why not Teflon release layer ?

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

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

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

Valve closing

Valve operation

Flow switch

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