3/8/2007

Solvent for PDMS
Filed under: Chemistry,Engineering,General,PDMS,Technology — nobrainer @ 10:44 am

So, you’re looking for a PDMS solvent. I bet you’re having a difficult time, and mostly finding scholarly articles that you either can’t access or that don’t actually have what you’re looking for. Well I’m going to provide some summary data for a very useful paper published in 2003 by Jessamine Ng Lee, Cheolmin Park, and George M. Whitesides. In their paper, Solvent Compatibility of Poly(dimethylsiloxane)-Based Microfluidic Devices, (you may be able to access the abstract and full text versions here), they report on the efficacy of various solvents for cross-linked PDMS.

For 38 different potential solvents, they immersed their samples of cross-linked PDMS and measured the amount of swelling. Most solvents won’t dissolve PDMS. The best solvents and the measured swelling ratios are listed below, along with a few very common, but less efficacious solvents. (Below all that are the chemicals that can completely dissolve the PDMS.)


Solvent Swelling Ratio
diisopropylamine 2.13
triethylamine 1.58
pentane 1.44
xylenes 1.41
chloroform 1.39
ether 1.38
tetrahydrofuran 1.38
hexanes 1.35
trichloroethylene 1.34
n-heptane 1.34
   
toluene 1.31
benzene 1.28
acetone 1.06
ethyl alcohol (ethanol) 1.40

If you actually want to dissolve PDMS, the paper says that 3 different items will do it: dipropylamine, sulfuric acid (18.0 mol/L), and trifluoroacetic acid (13.4 mol/L). It also notes that it took 39 days for the dipropylamine to completely dissolve the PDMS. It is important to note that these processes may all take days or weeks to complete.

UPDATE [2010-03-07]: A copy of the paper I was referring to has been uploaded to Scribd.

3/7/2007

Thoughts on the effects of acetone in your fuel system
Filed under: Acetone & Gasoline,Energy,Engineering,PDMS,Technology — nobrainer @ 12:45 pm
Looking for info on solvents for PDMS? Click here

In the whole debate about whether or not acetone can improve your fuel mileage, there is some conversation about whether or not acetone will damage your fuel system, particularly seals, hoses, and gaskets. I think everyone who comments is really just speculating, and I am going to chime in on the basis that I have no idea whether or not damage is actually occurring. However, there are several, potentially mistaken although somewhat logical, hypotheses being floated around. Here I’m just addressing what those ideas are and why they aren’t necessarily reliable.

Here, off the top of my head, are the 4 things that I’ll focus on.
1.) I’ve used acetone for years and never had a problem.
2.) I put fuel system parts in a jug of pure acetone for an extended time (years?) and there has been no problem.
3.) Gasoline is a solvent. Acetone is a solvent. Gasoline doesn’t destroy a fuel system, ergo acetone won’t, either.
4.) Acetone comes in plastic bottles, ergo it doesn’t destroy polymers.

Let’s address these items:
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