Help on HMDS - promotes or prevents PDMS adhesion?

Sebastian J. Osterfeld sjo at
Mon Oct 30 19:30:04 PST 2006

Dear Labmembers,

I read conflicting information on what effect HMDS has on PDMS adhesion 
(to glass). Generally, HMDS displaces hydroxyl groups on a surface with 
methyl groups, which makes a hydrophilic oxide surfaces, which would 
otherwise have water adsorbed, more hydrophobic and more polymer-like, 
thereby improving adhesion of organic films like photoresist. But say 
instead of resist, I want to cure PDMS on glass, and have it stick well 
- how should I best prepare the wafer?

Some people seem to suggest that HMDS application will remove moisture, 
present methyl groups, and thus promote adhesion of freshly cured PDMS, 
just like for photoresist. Probably more people, however, use HMDS over 
a mold as a release agent so that PDMS can be peeled off better.

Can someone give a definitive answer, or maybe some tips especially how 
I can ensure good adhesion of PDMS, which is cured right on top of a 
glass wafer? My first guess would be that probably a good dry bake 
without HMDS is best.

With best regards,

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