Nathan,
Pasted below is the protocol for this in gas phase from an older email
from this list about the topic. Note that you don't need a plasma
cleaner as it look like your email implies, a cheap vacuum desiccator
with a roughing pump will work fine to do this in gas phase.
However, if you really want to use a liquid phase, FDTS is soluble in
most alcohols. Dissolve the liquid FDTS in methanol, and you can get
it to work (though I don't have a protocol for that handy). After
contacting, rinse off the unbound FDTS with another shot of pure
alcohol (whatever one you're using) and bake as below. Keep in mind
that you should store anything with an exposed silane in nitrogen or
argon when not in use.
Also, note that the purpose of the FDTS is not bonding to the PDMS.
PDMS will adhere (and bond under the right conditions) to an exposed
oxide. The FTDS blocks the oxide with a long fluorocarbon chain (the
silane bonds to the oxide, and the FC chain sticks up from the
surface).
- Kevin
---------- Forwarded message ----------
From: Kevin Paul Nichols
Date: Sat, Mar 27, 2010 at 11:22 AM
Subject: Re: [mems-talk] Best way to spin PDMS for making sheets?
To: General MEMS discussion
Nathan,
To get PDMS to come off, you don't need a very well controlled
hydrophobic layer. Just use perfluorodecyltrichlorosilane (FDTS)
applied in a vacuum desiccator, and then baked at ~110. You can find
FDTS suppliers here: http://www.chemexper.com/
1) Place your Si wafers (with no PDMS on them, this is just so you end
up with a long fluorinated molecule sticking up from the surface so
the PDMS will peel off easily later) in a vacuum desiccator connected
to house vacuum (do a google image search for vacuum desiccator to see
what these look like). 2) Place 10-20 uL of FDTS in a small container
(the top of an eppendorf tube works well) in the bottom of the chamber
(location doesn't matter much). 3) Pull house vacuum, and leave them
for ~2 hours (exact time will be more or less depending on the vacuum
strength and container size). 4) Bake the wafers at 110 for ~2 hours.
There are lots of methods out there to get higher contact angles, but
that will be good enough.
If you have a goniometer, measure the static contact angle and check
that it's at least 90 with DI water. If you don't have a goniometer
handy, just pipette (or somehow dispense) a few microliters of DI
water on the surface, and make sure that it forms tight balls that
roll around easily.
Also, keep in mind that most people use PDMS precisely because you
don't need to ablate, etch, or otherwise chemically attack it. You can
just use "soft lithography" which uses a stamp to mold the PDMS as it
cures. Si molds are common, but glass and metal (even CNC machined
brass molds are good enough for some microfluidic applications). There
are hundreds of papers out there describing it, if you're interested.
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