Monday, February 01, 2010

Lab mysteries and other annoyances.

One aspect of experimental science that never shows up on TV procedurals (NCIS, CSI) is the "lab mystery" - the simple procedure that's supposed to be a piece of cake, but turns out to be unnecessarily and surprisingly complicated.  Here's an example.  There's a material that is supposed to be photopolymerizable; it starts out as a liquid monomer, and under UV exposure it's supposed to polymerize into a gel.  We have some, and we also have a UV lamp.  As a simple test, we exposed the monomer to the UV for tens of minutes - no response.  I'm sure we'll figure this out, but this sort of thing never happens to Abby or the guys from Mythbusters....  Feel free to leave other examples of lab mysteries in the comments.

update:  Mystery resolved.  In this case, the answer seems to be "more power".   A much (~ 20x) brighter UV lamp works quite well.  The paper we're working from didn't really mention intensities, so I think we can be forgiven.  

15 comments:

Adam said...

The offset in your X vs magnetic field plot.

Anonymous said...

I'm assuming the monomer was not in a solution vial during polymerization right?

Grad said...

The other big class of lab mysteries are things that used to work just fine but that have mysteriously stopped working.

rohan said...

blast it with tonnes of power (get 10 UV lamps)

الباحث العربي said...

once I fabricated wafer using usual method , after drawing my pattern using EBL and evaporating. we measured the resistance for the fabricated chips , and it was open . I fabricated six more chips all of them were open . after further investigation it turns out that the gold electrodes in my chip don't conduct electricity they were complete insulators.

Ψ*Ψ said...

wrong UV wavelength? solution in glass or pyrex vial?

Doug Natelson said...

Anon@10:31 and Ψ*Ψ - Heh. No, no intervening UV absorbers. Just a test few drops on a coverslip, illuminated from above. It may be a question of total UV power. I'll post a follow-up when we figure it out.

Mark Betnel said...

I assume you've seen this, but just in case:

http://xkcd.com/683/

Anonymous said...

It may be due to amorphous aggregation, depending on the type of polymerization involved (free radical polymerization has a maximum distance between monomer units, for example). Or it could be divine punishment for Rick Perry being the governor.

pterid said...

Oh my god yes. And they can be heartbreaking. I spent all night on a synchrotron beamline where time sells for $10,000/day, looking for a phase transition that just wasn't there, because the thermometer was miscalibrated by 50 degrees.

CarlBrannen said...

Harry Collins has written on this problem (i.e. lab knowledge that isn't quite in the textbook). I met him in his book on gravity waves, "Gravity's Shadow".

An example he gave was the earlier lasers. Apparently people couldn't reproduce results because there were parasitics that people didn't know were important. Things like "how long and thick the wires are" were important, but you couldn't learn it from the articles. Instead, the knowledge was passed on by people visiting the labs of successful laser makers.

Anonymous said...

/I'm sure we'll figure this out, but this sort of thing never happens to [...] the guys from Mythbusters.... /

Dead wrong. You just don't see it. The Mythbusters shoot hours of video that never get on the air - all the attempted replications, blind alleys, dumb mistakes just like we all do in the lab.

Uncle Al said...

Degas it (vacuum; argon or nitrogen purge) to get out oxygen. Avoid contamination with redox-active metal ions, sulfur species, phenols, amines. Know your sensitizer absorption maximum wavelength.

Plastic eyeglass lens hardcoats are UV-polymerized. The test rig is EM shielded two electrodeless mercury lamps (minimize IR emission) pumped by a kilowatt microwave power source in a countercurrent nitrogen-purged tunnel. Benzil ketal sensitizer for hard UV, camphor quinone for blue and blacklight. Severe eye and skin radiation hazard.

If your fingernail beds turn blue you have inhaled too much (meth)acrylate monomer. Go home for the day.

DanM said...

I want to be a mythbusters intern. How cool would that be? My dream sabbatical.

Revathi said...

I dont seem to be able to reproduce the IR spectra of carbon nanotubes that I take after pelletising with KBr. It is always too less nanotubes, too much pressure on the pellet and one never gets the same spectra.