To all,

Here is a summary of the answers I received concerning PDMS.  A big
THANK YOU to all those who helped!!!   Marvin

MY ORIGINAL POSTING:

Dear MEMS experts,
I am interested in using PDMS films for microfluidics, deposited onto
glass or sputtered SiO2.  My questions are:

1- PDMS is said to bond well to different materials, and to itself, so
that bonding can be conducted at very low temperatures. Is this true?
2- does the glass or SiO2 surface need treatment prior to PDMS
spin-coating to enhance adhesion?   If so, please describe a procedure.
3- how to change the wetting characteristics of the films?
4- how thick a single film of PDMS can be deposited practically without
cracking?
5- how to handle and dispose of this material?  is PDMS toxic?

Thank you.  Marvin Zai
OMRON CORPORATION, Research and Development Headquarters, Tsukuba-city,
Japan

--------------------------------------

Date: Fri, 26 Mar 1999 08:21:45 +0100
From: LINDER Vincent 

Hello,

My name is Vincent Linder, PhD student working in collaboration with
several partner in Neuchatel and around (Switzerland). I'm actually
using Pdms, but I'm not experienced in film deposition of Pdms on
surfaces. Anyway, there are some hints that might help you:

Pdms binds to glass, silicium, plasitics, ... but the binding is
reversible.  Hence when Pdms is polymerized, you can peel it off the
surface (provided that the film is thick enough and the surface doesn't
have high aspect ratio structures). Pdms binding requires that both
surfaces are clean (dust free), no high tenperature are required.
Wetting properties are actually difficult to change, seems that plasma
treatement can produce hydrophilic surfaces, but these surfaces
undergoes reconstitution within hours or weeks. Pdms is not toxic (human
implent are made of some kind of Pdms), but must be handled with care to
avoid contamination of the monomers in lab.

Best regards,  Vincent Linder

=============================
Subject:  RE: Deposition of PDMS films
Date: Mon, 29 Mar 1999 09:12:24 +1000
From: "Wilson, Alan" 

Answers in text below

> 1- PDMS is said to bond well to different materials, and to itself, so
>    that bonding can be conducted at very low temperatures. Is this true?
Yes.  Adheres well at room temperature. A cured PDMS film aheres very
nicely
to clean SiO2.

> 2- does the glass or SiO2 surface need treatment prior to PDMS spin-coating
>   to enhance adhesion?  If so, please describe a procedure.
I recall that brief exposure in an oxygen plasma enhanced adhesion for
cured
PDMS films. Since it is a siloxane anything that promotes a clean oxide
surface will enhance adhesion.

> 3- how to change the wetting characteristics of the films?
No direct knowledge on this. PMDS is rather viscous. It flows better at
higher temperature but of course cures faster.

> 4- how thick a single film of PDMS can be deposited practically without
cracking?
I have made gaskets up to 20mm thick and 20mm high essentially by
pouring
the PDMS into a level mold and then letting gravity do the rest.

> 5- how to handle and dispose of this material?  is PDMS toxic?
Ask the manufacturer but I do not recall any particularly stringent
handling procedures.

=======================================

Subject: RE: Deposition of PDMS films
Date: Fri, 26 Mar 1999 09:06:49 -0500
From: David Duffy 

**Marvin
**Answers below

1- PDMS is said to bond well to different materials, and to itself, so
   that bonding can be conducted at very low temperatures. Is this true?

**PDMS adheres very well to any surface containing silanol groups,
including glass and Si, by plasma oxidizing both surfaces prior to
bringing them into contact. Details in Duffy et al. Analytical Chemistry
1998, 70 (23), pp 4974-4984.

2- does the glass or SiO2 surface need treatment prior to PDMS
spin-coating to enhance adhesion?  If so, please describe a procedure.
**again plasma oxidation migt help

3- how to change the wetting characteristics of the films?
**Details of changing surface chemistry are given in the Anal Chem paper

4- how thick a single film of PDMS can be deposited practically without
cracking?
**Details of spin coating are given in Jackman, Duffy, Cherniavskaya and
Whitesides in an article due to be published soon by Langmuir (March
30th I think)

5- how to handle and dispose of this material?  is PDMS toxic?
**Its very safe if a little messy.

**Hope this helps  **david,