If you’ve read the preview, yes, there will be skydiving involved. Yes, there is science involved. No, there isn’t any science involving what happens when parachutes fail, and I’m not going to riff on that either. I’m not that crass.
A recent article published in the European Journal for Inorganic Chemistry highlights the research of an Austrian-Australian team of scientists where they wanted to control the size and shape of Metal-Organic Frameworks, or MOFs. Without going into a lot of detail (unless you really want to), MOFs are very porous materials; it’s pretty much a sponge cake at the molecular level. And like some sponge cake recipes out there, you can fill those pores with stuff (see the picture below, the yellow glob is ‘stuff’). Instead of maybe condensed milk, it’s individual gas molecules. However, these frameworks contain more space than stuff, so it’s got impressive surface area: according to the article, one gram of MOFs can cover an area up to 7000 square meters. It’s the size of a small suburban neighborhood, but only weighing as much as a couple of Tic Tacs. Deal with that.
Are they hard to make? Well, remember crystal growing kits? It’s like that, only much, much, MUCH harder because you’ve got to get the crystals to be the right size, the pores have to be the right shape and size, they’ve got to be stable in any temperature and probably not dissolve in water. It’s kind of like what one could do with silk filters, except you want the option to extract all the stuff that’s in the pores. But if you can get it to work (and there are plenty of studies that have; it’s rather popular research), there’s a lot of stuff you can do with it, from remote sensors and batteries to optics and environmental filters. And remember, it can cover a lot of area, so you may not even need that much of it around.
One of the issues that the researchers wanted to address was controlling the size of the size and shape of the particles without using additional chemicals. Sounds like a plan: less stuff that may pollute, not to mention less stuff to buy (you think your coffee run bills are bad after a month, buying chemicals can add up very quickly). They wanted to do this by exposing it to different amounts of gravity, which I’m referring as g (a measure of gravity relative to the Earth, set at 1 g) from now on. High-g is easy, just put it in a centrifuge like what they (and researchers before them) did:
It will squash the MOFs to the bottom of the tube, so you end up with densely-packed material with smaller pores. Instead of sponge cake, you get a muffin (I refuse to say MOF-fin, I’m not a dad, I’m not qualified to make dad jokes). But what if you want a fluffier MOF? What if you don’t want to make muffins, and you want angel food cake instead?
Well, angels fly, so why not take to the skies?
I don’t know if that’s how Richardson et al. decided their next method (that segue could have been less painful, yeesh), but I would’ve loved to have been at the meeting when someone had the brilliant idea to go skydiving. See, one experiences microgravity (feeling less than 1 g pulling you to the earth) when in free-fall. They tried dropping it; it works, but you can only do it for about 3 seconds max. Sure, the MOFs form, but what if you need more time for the crystals to grow? According to the paper (and this is the exact quote, I love this):
“Prolonged periods (10-15s) of low g were generated by skydiving out of an airplane (ca. 4000 m), with the use of a parachute to minimize the gravitational challenges after freefall.”
I love the phrase “with the parachute to minimize the gravitational challenges after freefall.” This is the paper-academic version of “we used parachutes so we don’t smash into the ground like tomatoes.” They could’ve just sent a drone that high and then dropped it, but it was important that the material already be mixed just before exposing it to high or low g. The reaction happens pretty quick (it was pretty far along even after just 3 seconds), and they wanted to get the crystals growing while it’s exposed different g conditions, not before. So, the team chartered a plane to simulate microgravity for an extended period of time because (also according to the paper) it’s a lot cheaper than, say, sending it to the International Space Station. So they went up, mixed the MOF samples, and jumped off the plane. Simple.
But apart from a thrill, did microgravity affect MOF growth at all? Turns out it did – it confirmed what had been done in the literature, which said that you can get larger pores through microgravity. However, no one’s ever exposed it to microgravity for that long, I don’t think. This means that this fluffy sponge cake of a MOF could capture larger particles like sulfur hexafluoride, a gas that can do some really funky stuff with your voice, but it’s also a greenhouse gas. Then again, it shouldn’t really be a surprise that gravity affects the growth of anything. For example, your muscles get pretty weak when you’ve been in low-gravity for a while. I’m not sure about the effects of high gravity on muscle growth, though.
Like a lot of studies on materials (I’ve had quite a few posts on those lately), of course it’s small scale. How they’re going to make it on an industrial scale is another thing. Then again, what is industrial scale for a material with that much surface area? How much of it do you really need? If you don’t need so much, and you can make it with less (possibly polluting and definitely expensive) materials, then engineering a way to make enough MOFs for use outside of research is possible. Maybe program drones to mix it while it’s up there? Mankind has the robotics know-how, plus we can print the parts we need. You’re welcome for the idea. It’s what we do here in sci.casual.
So what did we learn today?
- Gravity affects the growth of crystals.
- You can do some really nifty stuff with a tiny amount of MOFs.
- When writing for a paper for other academics, you can’t just write casually (even if it can be more straightforward).
- Bad science is a fate worse than death for most scientists, and that’s how we live. #scilife
- You can’t find all the good stuff only in the lab, just ask these people.
By the way, skydiving may make your MOFs fluffier, but it’s probably not enough to make your pastries fluffier, so do us a favor don’t try it. Just use eggs and an egg beater,OK?
Featured article: Richardson JJ, Liang K, Lisi F, Björnmalm M, Faria M, Guo J, Falcaro F. (2016) Controlling the Growth of Metal-Organic Frameworks Using Different Gravitational-Forces. Eur. J. Inorg. Chem. 10.1002/ejic.201600338
Featured image credit: U.S. Army (public domain)