Wednesday, 2 March 2016

5phases1cup: Dry Ice in Pluronic Gel

Today a 0.1 mL vial of DNA that I ordered arrived in the lab. It was shipped in a box 100,000 times its size, full of dry ice to keep it cold. Not wanting to let the dry ice go to waste and make my CO2 emissions productive, I decided to drop it in a vial of pluronic gel that another postdoc in my lab prepared. Let's take a look at what happened, and then I'll explain.

A stabilized version can be found here.

Pluronic is an ABA tri-block co-polymer, meaning that it has three regions of repeating chemical units, and the outer two are the same. When it's above a critical temperature, it collapses into a micelle with the out part forming a protective ball around the inner part. These micelles form a network and behave like a gel, but if the temperature is lowered it reverts back to a liquid, sort of like an re-un-boilable egg.

This image cannibalized from a google image search for pluronic.

When I dropped the dry ice in the pluronic, it landed on top of the gel and quickly cooled the region immediately below it, turning it liquid. This wave of cold slowly propagated downward, liquifying the gel in the process. Gravity gradually brought the ice pellet towards the bottom as it cleared out its own passage downward.

The slow but inexorable pull of gravity brings the dry ice pellet down to the bottom of the vial as it clears its own path via a wave of liquefied gel. This is easier to see in the stabilized video.
The CO2 sublimated into bubbles which floated upwards, leaving a sticky pluronic foam at the top which gradually overflowed out of the vial. Eventually, the liquid around the dry ice got so cold that it started undergoing an actual liquid-solid phase transition, encasing the pellet in H2O ice (possibly with pluronic mixed in?), limiting the region from which the bubbles emerged.

That's what's up.

So during this process, we had gel, liquid, gas, and two kinds of ice. Science is cool!

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