Creating The Perfect Ice Cube

8:20 minutes

Researchers created ice crystals with a near-perfect cubic arrangement of water molecules, in order to better understand how high-altitude ice clouds interact with sunlight and the atmosphere. In this X-ray diffraction image, the ice crystals have scattered X-rays to create concentric rings, which are a fingerprint of the molecular arrangement within the crystals. Image courtesy of The Ohio State University.

Did you know that not all ice is created equal? The stuff that solidifies in your freezer, as well as almost all natural forms of snow and ice on earth, is called hexagonal ice, so-named for the pattern the crystals form as they take shape. But there’s also cubic ice, a very rare form of ice that occurs naturally only in earth’s upper atmosphere. In the lab, cubic ice can only be made by quickly supercooling water to a very low temperature, essentially “tricking” the crystals into arranging themselves into a cubed pattern.

Barbara Wyslouzil, a professor of chemical and biomolecular engineering at Ohio State University, came as close as any scientist has come to creating perfectly cubed ice. She joins Ira to talk about the properties of cubic ice and why we study it. Then we introduce our latest Science Club: the Freeze Challenge!

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Segment Guests

Barbara Wyslouzil

Barbara Wyslouzil is a professor of chemical and biomolecular engineering at Ohio State University in Columbus, Ohio.

Segment Transcript

IRA FLATOW: And now for some science to help you stay cool as we head into the dog days of summer. Did you know that not all ice is created equal? Nope, that stuff that comes out of your freezer, it’s called hexagonal ice because it’s crystals form in a pattern shaped like a hexagon. Absolutely. It’s the same form that almost all natural snow and ice take on earth.

But there’s also something called cubic ice. No, it’s not the thing you pop into a glass before you pour your beverage. It’s not an Ice cube. Cubic ice is very special and can only be made by super cooling water to a very low temperature very quickly. It’s sort of tricking the crystals into arranging themselves into a cube pattern.

It’s not an easy thing to do, but my next guest has come as close as any scientist has to creating perfectly cubed ice. Joining me now is Barbara Wyslouzil. She is professor of chemical and biomolecular engineering at Ohio State University. Welcome to Science Friday.


IRA FLATOW: Well, when did we first learn that there was such a thing as cubic ice?

BARBARA WYSLOUZIL: Well, there were these phenomena noted in the atmosphere of halos that had a very special distance from the sun, so they couldn’t be explained by the presence of hexagonal ice. And so people did calculations to show that it’s possible, if the ice has a cubic crystal structure and the morphology, that the size of the crystal comes out reflecting that, or the shape of the crystal comes out reflecting that, then you could explain these halo phenomena.

IRA FLATOW: And, of course, once you discover it it exists, like any geeky scientist, you have to make one for yourself. You have to make that cubic ice.

BARBARA WYSLOUZIL: Yeah, you have to try. You have to try. And so what’s been interesting is that for a long time people figured out, or thought they were making cubic ice, and in the last, I would say 10 years, that whole idea of there being pure cubic ice was called into question. And so now what we talk about more is stacking disordered ice and try to characterize how much of that stacking disordered ice looks like cubic ice and how much does not.

IRA FLATOW: So you can’t make 100% cubic ice, but you can get how, how high?

BARBARA WYSLOUZIL: Well, we got up to close to 80%.


BARBARA WYSLOUZIL: And yes, and so that– there’s still some question whether you can make pure cubic ice, but certainly in the lab, I would say 80% is about as good as you can go, especially if you’re making it by freezing from supercooled liquid water.

IRA FLATOW: All right. Tell us the rest of the process. How do you make cubic ice?

BARBARA WYSLOUZIL: So the way we make cubic ice is that we have this device called a supersonic nozzle. And it– what we do is we take water vapor and nitrogen, so we basically take moist air and we flow it across this specially shaped nozzle and the gas expands and gets cold. And as it gets cold, the water vapor says, I don’t want to be a water vapor molecule anymore and it condenses to form very, very small liquid droplets. So those droplets are only about the millionth of the diameter– one of our droplets is about a million times smaller than the diameter of a rain droplet. And so since you have a really small droplet and you made it when it was really cold, then when it freezes, it’s freezing at a much colder temperature than you could make a normal droplet freeze.

IRA FLATOW: This is Science Friday from PRI, Public Radio International. I’m Ira Flatow, talking with Barbara Wyslouzil. She is professor of chemical and biomolecular engineering at Ohio State, talking about making cubic ice. If I were to look at a piece of cubic ice, would I notice any difference in the way it looks from regular ice?

BARBARA WYSLOUZIL: It would depend. So our droplets, our ice crystals are way too small to look out by eye, and so we have to use a technique called wide angle x-ray scattering to probe the structure of the ice, and that’s really the definitive way of telling what the crystal structure is that you have. So there are some electron micrographs that other people took that show, if you condense water vapor onto a cold substance, that under some conditions, you can actually see little cubes, which suggests that the ice is largely cubic. But mostly we have to rely on indirect methods to tell us what the structure is that we’ve made.

IRA FLATOW: So I’m not about to go up and order a bourbon on the rocks and get any cubic ice real soon?

BARBARA WYSLOUZIL: No, it wouldn’t survive cubic ice is very transient and fragile. So if you bring cubic ice up in temperature, bam, it goes over to a hexagonal ice and you’ve just got your refrigerator ice again.

IRA FLATOW: I hate it when that happens, don’t you?



IRA FLATOW: So you know what we always ask scientists, and what the public always wants to know is, what is this good for?

BARBARA WYSLOUZIL: What is this good for? Well, we want to understand how clouds work and there’s lots of calculations that show that if cubic ice exists in the atmosphere, it’s going to exist in the very high clouds that are really cold. And then the way that those clouds interact and evolve can depend on the kind of structure of the ice that’s there. So it might make bigger crystals. It might make fewer crystals.

And then, the way that interacts with sunlight is going to be affected by the properties of the cloud. From a– I’m more of a fundamental scientist and so I’m just interested in understanding the properties of water. And so water is like one of the most important, or if not the most important molecule on this planet for life. And so people are trying to be able to understand and predict how water is going to behave. And they mostly understand it, but when you have to choose between something like cubic and hexagonal lice which are pretty close in behavior, then it really provides a good way to test our understanding of the behavior of water and then gives us more confidence that we can predict what water is going to do under different circumstances.

IRA FLATOW: Considering how cold it might be on some planets in our solar system out there and how little vapor pressure there might be, could we be finding more cubic ice on those planets?

BARBARA WYSLOUZIL: Yeah. So the other place where cubic ice might matter is on asteroids and in interplanetary kind of situations. And on, like, the moons of other planets.

IRA FLATOW: Fascinating. You know, we always think we know so much about water, but there’s still so much to know, isn’t there?

BARBARA WYSLOUZIL: Oh, absolutely.

IRA FLATOW: Barbara Wyslouzil is professor of chemical and biomolecular engineering at the Ohio State University. Thank you, doctor.

BARBARA WYSLOUZIL: Thank you so much, Ira.

IRA FLATOW: Good to have you with us today. You’re welcome. Craving if you want more icy science in this hot summer weather? Well then, you’re going to love our newest science club. It’s the Freeze Challenge. We want you to invent something frozen. Maybe it’s totally new kind of ice cream or a toy to entertain your dog. You could use ice to create a new mode of transit or engineer a hat that keeps you cool. Be as creative and as silly as you want. Go to sciencefriday.com/scienceclub for some projects to get you started, like super cooling frozen fruit pops. Mmm. Creating instant ice. Share your submissions on Twitter and Instagram and on our web site all month long with hashtag, Sifrisiclub.

That’s about all the time we have for this hour. Charles Bergquist is our director, senior producer, Christopher Intagliata. Our producers are Alexa Lim, Christie Taylor, Katie Hiler. Our show was engineered today by Neil Rouch and thanks also to Brian McCabe and the folks at NPR. If you’d like to write us, go to our website at sciencefriday.com, where we are tweeting and doing everything and, you know, social communities all week. Every day is Science Friday on the web. Have a great weekend. I’m Ira Flatow in New York.

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