Nobrainer’s Think Tank

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.

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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I’ve previously cast my thoughts on the acetone improves mileage concept. I still think it’s a myth, but like the good little scientist I am, I’m always up for being proven wrong. It turns out that the main propagator of the idea, Lou LaPointe (who also goes by C. L. LaPointe, and Louis LaPointe), updated his files sometime in 2006.

There is a lot of stuff to read, but not very much useful information; it’s rather long winded, ill organized, and full of entirely too much conspiracy theory. To avoid being long winded myself, there are 4 main points I want to hit on today.

1.) Have you read the finer details of his testing?
2.) Did you notice he says that it’s not just acetone that works as a mileage enhancing additive? Let’s look more at xylene, and some of the others.
3.) There’s a researcher at Clemson University who has confirmed positive results?
4.) If it’s a surface tension problem, let’s study that.

To some extent this is incomplete and ongoing research. This is the presentation of what I’ve found thus far.

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I’ve said it. You’ve said it. Our mothers have said it. Our fathers have said it. Our fathers’ brothers’ cousins’ nephews’ former roommates have said. And it’s stupid. There shouldn’t be a law.

Why? Because people who make laws say that. They believe it. Then they make a law. It’s usually a stupid law.

For example, mandating child car seats. They’re expensive, bulky, and not necessarily a major safety improvement. And they’re often misused. From an article in the St. Paul Pioneer Press:

The Minnesota Safety Council estimates more than 80 percent of child car seats used in Minnesota are not properly installed.

I was just about mention that Freakonomics talked about car seats and their worthlessness a bit. So I just went to their blog to search for any content they had about car seats. Well “search” turned into the 2nd visible post on their blog today. Consumer Reports recently found:

When we crash-tested infant car seats at the higher speeds vehicles routinely withstand, most failed disastrously. The car seats twisted violently or flew off their bases, in one case hurling a test dummy 30 feet across the lab.

CONGRATULATIONS! You just spent your money on a government mandated piece of shit! But remember, car seats are for “the greater good” and “for the children” and “for the future.”

But there was another article that caught my attention today. In part it was because a drunk crashed his truck and collapsed a whole bridge. But as I read it commented on his BAC.

A preliminary breath test at the crash site showed Campbell’s blood-alcohol content at .21, nearly three times the legal limit of .08. He blew .13 after completing field sobriety tests and a Datamaster test showed .147.

Hows that for accuracy and precision! Do the police use the average? The min? The max? The median? The mode? The average was .162 with a standard deviation of .042… or about 25% of the average. Hey, it’s close enough for government work!

And I almost forgot to rant about other stupid legislation, such as nutrition labels and movie, tv, and video game ratings. What has this information done? Made us fatter and focus on adult, R-rated, and most extreme video games. FUCK YEAH!

[Editor's note: In recent tests, I got only a moderate, 5%-8% (if that much), improvement due to acetone. Also, click the above Acetone & Gasoline link to see the most recent posts on the topic.]

Mythbusters finally tackled the issue and tested car performance with acetone mixed with gasoline. Was the mileage improvement touted by Louis Lapointe confirmed? Plausible? No. And no. Totally busted.

They didn’t test the full range of mixtures, but said they used about a 500:1 gasoline:acetone ratio. That’s about 2.56 fluid ounces per 10 gallons.

Just like the engineers at Kettering University, no improvement due to acetone was found. In fact, it looked as though mileage was decreased in all four of their scenarios (2 speeds times 2 cars) on the dyno.

I’m SHOCKED!

UPDATE: whoops! I thought tonight’s episode was new. I was wrong, according to Wikipedia it aired on May 10, 2006. And crazy ol’ LaPointe defends himself in his FAQ (seriously, read it and decide for yourself that the guy is nuts): (more…)

It turns out I’ve been taking the wrong approach to my school work. Indepedent work, what’s all that about?

I should be embracing the ethics of my peers. “54 percent of graduate engineering students admitted to cheating.”