Go With the Flow – A First Week Back in Lab

I’ve recently moved in, got my bearings, cleaned like crazy and come back to lab. For the Chemistry department, the week started off with a Safety Seminar and tour of the Integrated Science Center – including some modeling of lab coats, a rarely seen peak of the neutralization system, and fire safety training.

After that fairly easy start to the summer (aside from the whole nerve-wracking putting-out-fires-in-a-training-system-in-front-of-your-peers thing) it was back to lab work. I’ve been logging which procedures I work with each day in a personal notebook — this is proving to be very helpful to blogging.

This week I’d like to tell you all a little bit about CIV (Corrected Intrinsic Viscosity). Why this week? Well, it’s the beginning of the summer, research students are off to the races so to speak, and I always imagine the CIV procedure as a sort of little race. You’ll see.

Corrected Intrinsic Viscosity is an indirect method of measuring the weight of a polymer. Viscosity is defined by Wikipedia as “a measurement of its resistance to gradual deformation by shear stress or tensile stress.” I think that’s a bit wordy for a casual discussion. I prefer to think of viscosity as ‘flowiness’ – honey flows more slowly than water, so honey has a high viscosity than water, for example.

Viscosity is related to the molecular weight of a polymer solution — longer, heavier chains slow down the flow of the solution compared to pure solvent. This is observable but it is also measurable. To measure the CIV of an aged polymer sample, we prepare our sample of polymer and then run it, as in this step-by-step process.

Step 1: Chop a bit of polymer sample into small pieces — surface area is important! Tinier pieces are much better at dissolving.

Step 2: Dry the chopped up sample in the oven – we’re getting the water out and our sample entirely dry.

Whew, it’s hot in here!

 

Step 3: Mass our samples on the 4-digit scale, and record.

Step 4: Calculate, via a spectacular spreadsheet, the amount of solution we need to add for each mass of sample. Add the appropriate amount of solvent with care. Our solvent is m-cresol — it doesn’t smell great (understatement alert!), and it is corrosive but it does the job.

An unnecessarily artistic photo of clean CIV sample bottles

Adding the proper amount of m-cresol

 

Step 5: Load the Viscometers! You can run up to three at a time. The viscometers look like this:

 

 

The one on the far left is for an entirely different project so we aren’t concerned with it right now. These are Ubbelohde viscometers. The loaded solution is in the bottom ‘bubble’ – ours are a kind of pinkish/brownish color.

 

Step 6: Run the samples.

The solution is sucked up into the ‘top bubble’ using a little bulb. It then slowly flows back through the glassware to the bottom. This is the part that looks a little like a race — at least that’s how I like to imagine it.

Who’s going to win?

 

In this case, the sample on the far left is going to finish first. We time the how long it take for the meniscus to go from the top line above the bubble to the bottom line below it, using a stopwatch. It takes a lot of practice to run three at a time but its a lot more fun if you pretend the samples are having a bit of race. From here on, its all data keeping and math.

 

Until next week,

Natalie

 (P. S. All photos included are ones I took, but man of the keywords are hyperlinked to the Wikipedia page for that concept, in case anybody wants to look at more diagrams/structures/etc.)