What is rheology?

Inspired by NaBloPoMo and THE CENTRIFUGE NOT WORKING RIGHT THE FIRST TIME SO I HAVE TO STAY IN LAB FOR THREE MORE HOURS THAN I PLANNED (this was more relevant when I tried writing this a few weeks ago), I’ll be trying to post more often this month. Though heaven knows I’m not even going to pretend I’ll get a post a day when I have a conference (!) to prepare for.

I figure my first post could be a better attempt at better describing a major part of my research now – rheology and rheometers. The somewhat uncommon, unless you’re a doctor or med student who sees it pop up all the time in words like gonorrhea and diarrhea, Greek root “rheo” means “flow”, and so the simplest definition is that rheology is the study of flow. (And I just learned the Greek Titan Rhea’s name may also come from that root, so oh my God, rheology actually does relate to Rhea Perlman.) But what does that really mean? And if you’ve tripped out on fluid mechanics videos or photos before, maybe you’re wondering “what makes rheology different?”

RheaPerlmanAug2011.jpg

Oh my God, she is relevant to my field of study.

For our purposes, flow can mean any kind of material deformation, and we’re generally working with solids and liquids (or colloid mixtures involving those states, like foams and gels). Or if you want to get really fancy, you can say we’re working with (soft) condensed matter. Why not gas? We’ll get to that later. So what kind of flow behavior is there? There’s viscosity, which is what we commonly consider the “thickness” of a flowing liquid. Viscosity is how a fluid resists motion between component parts to some shearing force, but it doesn’t try to return the fluid back to its original state. You can see this in cases where viscosity dominates over the inertia of something moving in the fluid, such as at 1:00 and 2:15 in this video; the shape of the dye drops is essentially pinned at each point by how much the inner cylinder moves, but you don’t see the fluid move back until the narrator manually reverses the cylinder.

The other part of flow is elasticity. That might sound weird to think of a fluid as being elastic. While you really don’t see elasticity in pure fluids (unless maybe the force is ridiculously fast), you do see it a lot in mixtures. Oobleck, the ever popular mixture of cornstarch and water, becomes elastic as part of its shear-thickening behavior. (Which it turns out we still don’t have a great physical understanding of.)

 

You can think of viscosity as the “liquid-like” part of a substance’s behavior and elasticity as the “solid-like” part. Lots of mixtures (and even some pure substances) show both parts as “viscoelastic” materials. And this helps explain the confusion when you’re younger (or at least younger-me’s questions) of whether things like Jell-O, Oobleck, or raw dough are “really” solid or liquid. The answer is sort of “both”. More specifically, we can look at the “dynamic modulus” G at different rates of force. G has two components – G’ is the “storage modulus” and that’s the elastic/solid part, and G” is the “loss modulus” representing viscosity.

The dynamic moduli of Silly Putty at different rates of stress.

Whichever modulus is higher what mostly describes a material. So in the flow curve above, the Silly Putty is more like a liquid at low rates/frequencies of stress (which is why it spreads out when left on its own), but is more like a solid at high rates (which is why is bounces if you throw it fast enough). What’s really interesting is that the total number of either component doesn’t really matter, it’s just whichever one is higher. So even flimsy shaving cream behaves like a solid (seriously, it can support hair or other light objects without settling) at rest while house paint is a liquid, because even though paint tends to have a higher modulus, the shaving cream still has a higher storage modulus than its own loss modulus.

I want to publish this eventually, so I’ll get to why we do rheology and what makes it distinct in another post.

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Weirdly Specific Questions I Want Answers to in Meta-science, part 1

Using “meta-science” as a somewhat expansive term for history, philosophy, and sociology of science. And using my blog as a place to write about something besides the physical chemistry of carbon nanomaterials in various liquids.

  • To what extent is sloppy/misleading terminology an attempt to cash in on buzzwords? Clearly, we know that motive exists – there aren’t two major papers trying to narrow down precise definitions of graphene-related terms for nothing. But as the papers also suggest, at what point is it a legitimate debate in the community about setting a definition? “Graphene” was a term that described a useful theoretical construct for decades before anyone ever thought* someone could make a real sheet of it, so maybe it isn’t unreasonable that people started using it to describe a variety of physical things related to the original idea.
    • This contains a sort of follow-up: What properties do people use in clarifying these definitions and how much does it vary by background? Personally, I would say I’m way closer to the ideal of “graphene” than lots of people working with more extensively chemically modified graphene derivatives and am fine with using it for almost anything that’s nearly all sp2 carbon with about 10 layers or less. But would a physicist who cares more about the electronic properties, and which vary a lot based on the number of layers even in the lower limit, consider that maddening?
  • Nanoscience is very interdisciplinary/transdisciplinary, but individual researchers can be quite grounded in just one field. How much work is being done where researchers are missing basic knowledge of another field their work is now straddling?
    • For instance, when reading up on polymer nanocomposites, it seems noted by lots of people with extensive polymer science backgrounds that there are many papers that don’t refer to basic aspects of polymer physics. My hunch is that a lot of this comes from the fact that many people in this field started working on the nanoparticles they want to incorporate into the composites and then moved into the composites. They may have backgrounds more in fields like solid-state physics, electrical engineering, or (inorganic/metallic/ceramic) materials science, where they would have been less likely to deal with polymer theory.
    • Similarly, it was noted in one paper I read that a lot of talk about solutions of nanoparticles probably would be more precise if the discussion was framed in terminology of colloids and dispersions.
51cb2b3noc-l-_sx346_bo1204203200_

Oh my gosh, I made fun of the subtitle for like two years, but it’s true

  • Is the ontological status of defects in nanoscience distinct from their treatment in bulk studies of materials? This is a bit related to the first question in that some definitions would preclude the existence of some defects in the referent material/structure.
    • On the other hand, does this stricter treatment make more sense in the few atom limit of many nanomaterials? Chemists can literally specify the type and location of every atom in successful products of well-studied cluster reactions, though these are even pushing the term “nano” (though in the sense they may be too small).
    • Is this a reflection of applications of defects at the different scales? (More philosophically worded, are defects treated differently because of their teleological nature?) At the bulk level, we work to engineer the nature of defects to help develop the properties we want. At the nanoscale, some structures can basically be ruined for certain applications by the mislocation of a single atom. Is this also a reflection of the current practical process of needing to scale up the ability to make nanomaterials? E.g. as more realistic approaches to large-scale nanotech fabrication are developed, will the practical treatment of defects in nanomaterials converge to that of how we treat defects in the bulk?

*Okay, more like anyone cared a lot about it, since there are papers going back to the 1960s where researchers describe what appear to be atomic monolayers of graphite.

So What is Materials Science (and Engineering)?

So this is my 100th post, and I felt like it should be kind of special. So I want to cover a question I get a lot, and one that’s important to me; what exactly is materials science? My early answer was that “it’s like if physics and chemistry had a really practical baby.” One of my favorite versions is a quote from this article on John Goodenough, one of the key figures in making rechargeable lithium ion batteries: “In hosting such researchers, Goodenough was part of the peculiar world of materials scientists, who at their best combine the intuition of physics with the meticulousness of chemistry and pragmatism of engineering”. Which is a much more elegant (and somewhat ego-boositng) way of wording my description. In one of my first classes in graduate school, my professor described materials science as “the study of defects and how to control them to obtain desirable properties”.

A more complete definition is some version of the one that shows up in most introductory lessons: materials science studies the relationship between the structure of a material, its properties, its performance, and the way it was treated. This is often represented as the “materials science tetrahedron”, shown below. Which turns out to be something people really love to use. (You also sometimes see characterization float in the middle, because it applies to all these aspects.)

A tetrahedron with blue points at the vertices. The top is labelled structe, the bottom three are properties, processing, and performance.

The materials science tetrahedron (with characterization floating in the middle).

Those terms may sound meaningless to you, so let’s break them down. In materials science, structure goes beyond that of chemistry: it’s not just what makeup of an atom or molecule that affects a material, but how the atoms/molecules are arranged together in a material has a huge effect on how it behaves. You’re probably familiar with one common example: carbon and its various allotropes. The hardness of diamond is partially attributed to its special crystal structure. Graphite is soft because it is easy to slide the different layers across each other. Another factor is the crystallinity of a material. Not all materials you see are monolithic pieces. Many are made of smaller crystals we call “grains”. The size and arrangement of these grains can be very important. For instance, the silicon in electronics is made in such a way to guarantee it will always be one single crystal because boundaries between grains would ruin its electronic properties. Turbine blades in jet engines and for wind turbines are single crystals, while steels used in structures are polycrystalline.

On the top is a diamond and a piece of graphite. On the bottom are their crystal structures.

Diamond and its crystal structure is on the left; graphite on the right.

Processing is what we do to a material before it ends up being used. This is more than just isolating the compounds you’ll use to make it. In fact, for some materials, processing actually involves adding impurities. Pure silicon wouldn’t be very effective in computers. Instead, silicon is “doped” with phosphorus or boron atoms and the different doping makes it possible to build various electronic components on the same piece. Processing can also determine the structure – temperature and composition can be manipulated to help control the size of grains in a material.

A ring is split into 10 different sections. Going counterclockwise from the top, each segment shows smaller crystals.

The same steel, with different size grains.

Properties and performance are closely related, and the distinction can be subtle (and honestly, it isn’t something we distinguish that much). One idea is that properties describe the essential behavior of a material, while performance reflects how that translates into its use, or the “properties under constraints“. This splits “materials science and engineering” into materials science for focusing on properties and materials engineering for focusing on performance. But that distinction can get blurred pretty quickly, especially if you look at different subfields. Someone who studies mechanical properties might say that corrosion is a performance issue since it limits how long a material could be used at its desired strength. Talk to my colleagues next door in the Center for Electrochemical Science and Engineering and they would almost all certainly consider corrosion to be a property of materials. Regardless, both of these depend on structure and processing. Blades in wind turbines and jet engines are single crystals because this reduces fatigue over time. Structural steels are polycrystals because this makes them stronger.

Now that I’ve thought about it more, I realize the different parts of the tetrahedron explain the different ways we define materials science and engineering. My “materials science as applied physics and chemistry” view reflects the scale of structures we talk about, from atoms that are typically chemistry’s domain to the crystal arrangement to the larger crystal as a whole, where I can talk about mechanics of atoms and grains. The description of Goodenough separates materials science from physics and chemistry through the performance-driven lens of pragmatism. My professor’s focus on defects comes from the processing part of the tetrahedron.

The tetrahedron also helps define the relationship of materials science and engineering to other fields. First, it helps limit what we call a “material”. Our notions of structure and processing are very different from the chemical engineers, and work best on solids. It also helps define limits to the field. Our structures aren’t primarily governed by quantum effects and we generally want defects, so we’re not redundant to solid-state physics. And when we talk about mechanics, we care a lot about the microstructure of the material, and rarely venture into the large continuum of mechanical and civil engineers.

At the same time, the tetrahedron also explains how interdisciplinary materials science is and can be. That makes sense because the tetrahedron developed to help unify materials science. A hundred years ago, “materials science” wouldn’t have meant anything to anyone. People studying metallurgy and ceramics were in their own mostly separate disciplines. The term semiconductor was only coined in a PhD dissertation in 1910, and polymers were still believed to be aggregates of molecules attracted to each other instead of the long chains we know them to be today. The development of crystallography and thermodynamics helped us tie all these together by helping us define structures, where they come from, and how we change them. (Polymers are still a bit weird in many materials science departments, but that’s a post for another day)

Each vertex is also a key branching off point to work with other disciplines. Our idea of structure isn’t redundant to chemistry and physics, but they build off each other. Atomic orbitals help explain why atoms end up in certain crystal structures. Defects end up being important in catalysts. Or we can look at structures that already exist in nature as an inspiration for own designs. One of my professors explained how he once did a project studying turtle shells from an atomic to macroscopic level, justifying it as a way to design stronger materials. Material properties put us in touch with anyone who wants to use our materials to go into their end products, from people designing jet engines to surgeons who want prosthetic implants, and have us talk to physicists and chemists to see how different properties emerge from structures.

This is what attracted me to materials science for graduate school. We can frame our thinking on each vertex , but it’s also expected that we shift. We can think about structures on a multitude of scales. Now I joke that being a bad physics major translates into being great at most of the physics I need to use now. The paradigm helps us approach all materials, not just the ones we personally study. Thinking with different applications in mind forces me to learn new things all the time. (When biomedical engineers sometimes try to claim they’re the “first” interdisciplinary field of engineering to come on the scene, I laugh thinking that they forget materials science has been around for decades. Heck, now I have 20 articles I want to read about the structure of pearl to help with my new research project.) It’s an incredibly exciting field to be in.

The Coolest Part of that Potentially New State of Matter

So we’ve discussed states of matter. And the reason they’re in the news. But the idea that this is a new state of matter isn’t particularly ground-breaking. If we’re counting electron states alone as new states of matter, then those are practically a dime a dozen. Solid-state physicists spend a lot of time creating materials with weird electron behaviors: under this defintion, lots of the newer superconductors are their own states of matter, as are topological insulators.

What is a big deal is the way this behaves as a superconductor. “Typical” superconductors include basically any metal. When you cool them to a few degrees above absolute zero, they lose all electrical resistance and become superconductive. These are described by BCS theory, a key part of which says that at low temperatures, the few remaining atomic vibrations of a metal will actually cause electrons to pair up and all drop to a low energy. In the 1970s, though, people discovered that some metal oxides could also become superconductive, and they did at temperatures above 30 K. Some go as high as 130 K, which, while still cold to us (room temperature is about 300 K), is warm enough to use liquid nitrogen instead of incredibly expensivve liquid helium for cooling. However, BCS theory doesn’t describe superconductivity in these materials, which also means we don’t really have a guide to develop ones with properties we want. The dream of a lot of superconductor researchers is that we could one day make a material that is superconducting at room temperature, and use that to make things like power transmission lines that don’t lose any energy.

This paper focused on an interesting material: a crystal of buckyballs (molcules of 60 carbon atoms arranged like a soccer ball) modified to have some rubidium and cesium atoms. Depending on the concentration of rubidium versus cesium in the crystal, it can behave like a regular metal or the new state of matter they call a “Jahn-Teller metal” because it is conductive but also has a distortion of the soccer ball shape from something called the Jahn-Teller effect. What’s particularly interesting is that these also correspond to different superconductive behaviors. At a concentration where the crystal is a regular metal at room temperatures, it becomes a typical superconductor at low temperatures. If the crystal is a Jahn-Teller metal, it behaves a lot like a high-temperature superconductor, albeit at low temperatures.

This is the first time scientists have ever seen a single material that can behave like both kinds of superconductor. This is exciting becasue this offers a unique testing ground to figure out what drives unconventional superconductors. By changing the composition, researchers change the behavior of electrons in the material, and can study their behavior, and see what makes them go through the phase transition to a superconductor.

What is a State of Matter?

This Vice article excitedly talking about the discovery of a new state of matter has been making the rounds a lot lately. (Or maybe it’s because I just started following Motherboard on Twitter after a friend pointed this article out) Which lead to two good questions: What is a state of matter? And how do we know we’ve found a new one? We’ll consider that second one another time.

In elementary school, we all learned that solid, liquid, and gas were different states of matter (and maybe if you’re science class was ahead of the curve, you talked about plasma). And recent scientific research has focused a lot on two other states of matter: the exotic Bose-Einstein condensate, which is looked at for many experiments to slow down light, and the quark-gluon plasma, which closely resembles the first few milliseconds of the universe after the Big Bang. What makes all of these different things states? Essentially a state of matter is the set behavior of the collection of particles that makes up your object of interest, and each state behaves so differently you can’t apply the description one to another. A crucial point here is that we can only consider multiple partcies to be states, and typically a large number of particles. If you somehow have only one molecule of water, it doesn’t really work to say whether it is solid, liquid, or gas because there’s no other water for it to interact with to develop collective properties.

So room temperature gold and ice are solids because they’re described by regular crystal lattices that repeat. Molten gold and water are no longer solids because they’re no longer described by a regular crystal structure but still have relatively strong forces between molecules. The key property of a Bose-Einstein condensate is that most of its constituent particles are in the lowest possible energy. You can tell when you switched states (a phase transition) because there was a discontinuous change in energy or a property related to energy. In everyday life, this shows up as the latent heat of melting and the latent heat of vaporization (or evaporation).

The latent heat of melting is what makes ice so good at keeping drinks cold. It’s not just the fact that ice is colder than the liquid; the discontinuous “jump” of energy required to actually melt 32°F  ice into 32°F water also absorbs a lot of heat. You can see this jump in the heating curve below. You also see this when you boil water. Just heating water to 212 degrees Fahrenheit doesn’t cause it all to boil away; your kettle/stove also has to provide enough heat to overcome the heat of vaporization. And that heating is discontinuous because it doesn’t raise the temperature until the phase transition is complete. You can try this for yourself in the kitchen with a candy thermometer: ice will always measure 32 F, even if  you threw it in the oven, and boiling water will always measure 212 F.

A graph with the horizontal axis labelled "Q (heat added}" and the veritcal axis labelled "temperature (in Celsius)". It shows three sloped segments, that are labelled, going from the left, ice, heating of water, and heating of water vapor. The sloped line for "ice" and "heating of water" are connected by a flat line representing heat used to melt ice to water. The "heating of water" and "heating of water vapor" sloped lines are connected by a flat line labelled "heat used to vaporize water to water vapor".

The heating curve of water. The horizontal axis represents how much heat has been added to a sample of water. The vertical axis shows the temperature. The flat lines are where heat is going into the latent heat of the phase transition instead of raising the temperature of the sample.

There’s also something neat about another common material related to phase transitions. The transition between a liquid and a glass state does not have a latent heat. This is the one thing that makes me really sympathetic to the “glasses are just supercooled liquids” views. Interestingly, this also means that there’s really no such thing as a single melting temperature for a given glass, because the heating/cooling rate becomes very important.

But then the latter bit of the article confused me, because to me it points out that “state of matter” seems kind of arbitrary compared to “phase”, which we talk about all the time in materials science (and as you can see, we say both go through “phase” transitions). A phase is some object with consistent properties throughout it, and a material with the same composition can be in different phases but still in the same state. For instance, there actually is a phase of ice called ice IX, and the arrangement of the water molecules in it is different from that in conventional ice, but we would definitely still consider both to be solids. Switching between these phases, even though they’re in the same state, also requires some kind of energy change.

Or if you heat a permanent magnet above its critical temperature and caused it to lose its magnetization, that’s the second kind of phase transition. That is, while the heat and magnetization may have changed continuously, the ease of magnetizing it (which is the second derivative of the energy with respect to strength of the magnetic field) had a jump at that point. Your material is still in a solid state and the atoms are still in the same positions, but it changed its magnetic state from permanent to paramagnetic. So part of me is wondering whether we can consider that underlying electron behavior to be a definition of a state of matter or a phase. The article makes it sound we’re fine saying they’re basically the same thing. This Wikipedia description of “fermionic condensates” as a means to describe superconductivity also supports this idea.

Going by this description then means we’re surrounded by way more states of matter than the usual four we consider. With solids alone, you interact with magnetic metals, conductors (metals or the semiconductors in your electronics), insulating solids, insulating glasses, and magnetic glasses (amorphous metals are used in most of those theft-prevention tags you see) on a regular basis, which all have different electron behaviors. It might seem slightly unsatisfying for something that sounds as fundamental as “states of matter” to end up having so many different categories, but it just reflects an increasing understanding of the natural world.

Carbon is Dead. Long Live Carbon?

Last month, the National Nanotechnology Initiative released a report on the state of commercial development of carbon nanotubes. And that state is mostly negative. (Which pains me, because I still love them.) If you’re not familiar with carbon nanotubes, you might know of their close relative, graphene, which has been in the news much more since the Nobel Prize awarded in 2010 for its discovery. Graphene is essentially a single layer of the carbon atoms found in graphite. A carbon nanotube can be thought of as rolling up a sheet of graphene into a cylinder.

CNT as rolled-up graphene.jpg

Visualizing a single-walled (SW) carbon nanotube (CNT) as the result of rolling up a sheet of graphene.

If you want to use carbon nanotubes, there are a lot of properties you need to consider. Nearly 25 years after their discovery, we’re still working on controlling a lot of these properties, which are closely tied to how we make the nanobues.

Carbon nanotubes have six major characteristics to consider when you want to use them:

  • How many “walls” does a nanotube have? We often talk about the single-walled nanotubes you see in the picture above, because their properties are the most impressive. However, it is much easier to make large quantities of nanotubes with multiple walls than single walls.
  • Size. For nanotubes, several things come in play here.
    • The diameter of the nanotubes is often related to chirality, another important aspect of nanotubes, and can affect both mechanical and electrical properties.
    • The length is also very important, especially if you want to incorporate the nanotubes into other materials or if you want to directly use nanotubes as a structural material themselves. For instance, if you want to add nanotubes to another material to make it more conductive, you want them to be long enough to routinely touch each other and carry charge through the entire material. Or if you want that oft-discussed nanotube space elevator, you need really long nanotubes, because stringing a bunch of short nanotubes together results in a weak material.
    • And the aspect ratio of length to width is important for materials when you use them in structures.
  • Chirality, which can basically be thought of as the curviness of how you roll up the graphene to get a nanotube (see the image below). If you think of rolling up a sheet of paper, you can roll it leaving the ends matched up, or you can roll it an angle. Chirality is incredibly important in determing the way electricity behaves in nanotubes, and whether a nanotube behaves like a metal or like a semiconductor (like the silicon in your computer chips). It also turns out that the chirality of nanotubes is related to how they grow when you make them.
  • Defects. Any material is always going to have some deviation from an “ideal” structure. In the case of the carbon nanotubes, it can be missing or have extra carbon atoms that replace a few of the hexagons of the structure with pentagons or heptagons. Or impurity atoms like oxygen may end up incorporated into the nanotube. Defects aren’t necessarily bad for all applications. For instance if you want to stick a nanotube in a plastic, defects can actually help it incorporate better. But electronics typically need nanotubes of the highest purity.

A plane of hexagons is shown in the top left. Overlaid on the plan are arrows representing vectors. On the top right is a nanotube labeled (10, 0) zig-zag. On the bottom left is a larger (10, 10) armchair nanotube. On the bottom right is a larger (10, 7) chiral nanotube. Some of the different ways a nanotube can be rolled up. The numbers in parentheses are the “chiral vector” of the nanotube and determine its diameter and electronic properties.

Currently, the methods we have to make large amounts of CNTs result in a mix of ones with different chiralities, if not also different sizes. (We have gotten much better at controlling diameter over the last several years.) For mechanical applications, the former isn’t much of a problem. But if you have a bunch of CNTs of different conductivities, it’s hard to use them consistently for electronics.

But maybe carbon nanotubes were always doomed once we discovered graphene. Working from the idea of a CNT as a rolled-up graphene sheet, you may realize that means there are  way more factors that can be varied in a CNT than a single flat flake of graphene. When working with graphene, there are just three main factors to consider:

  • Number of layers. This is similar to the number of walls of a nanotube. Scientists and engineers are generally most excited about single-layer graphene (which is technically the “true” graphene). The electronic properties change dramatically with the number of layers, and somewhere between 10 and 100 layers, you’re not that different from graphite. Again, the methods that produce the most graphene produce multi-layer graphene. But all the graphene made in a single batch will generally have consistent electronic properties.
  • Size. This is typically just one parameter, since most methods to make graphene result in roughly circular, square, or other equally shaped patches. Also, graphene’s properties are less affected by size than CNTs.
  • Defects. This tends to be pretty similar to what we see in CNTs, though in graphene there’s a major question of whether you can use an oxidized form or need the pure graphene for your application, because many production methods make the former first.

Single-layer graphene also has the added quirk of its electrical properties being greatly affected by whatever lies beneath it. However, that may be less of an issue for commercial applications, since whatever substrate is chosen for a given application will consistently affect all graphene on it. In a world where can now make graphene in blenders or just fire up any carbon source ranging from Girl Scout cookies to dead bugs and let it deposit on a metal surface, it can be hard for nanotubes to sustain their appeal when growing them requires additional steps of catalyst production and placement.

But perhaps we’re just leaving a devil we know for a more hyped devil we don’t. Near the end of last year, The New Yorker had a great article on the promises we’re making for graphene, the ones we made for nanotubes, and about technical change in general, which points out that we’re still years away from widespread adoption of either material for any purpose. In the meantime, we’re probably going to keep discovering other interesting nanomaterials, and just like people couldn’t believe we got graphene from sticky tape, we’ll probably be surprised by whatever comes next.

A Nobel for Nanotubes?

A popular pastime on the science blogosphere is doing Nobel predictions; educated guesses on who you think may win a Nobel prize in the various science categories (physics, chemistry, and physiology or medicine). I don’t feel like I know enough to really do detailed predictions, but I did make one. Okay, more of a dream than a prediction. But I feel justified because Slate also seemed to vouch for it. What was it? I think a Nobel Prize in Physics should be awarded for the discovery and study of carbon nanotubes.

One potential issue with awarding a prize for carbon nanotube work could be priority. Nobel prizes can only be split between three people. While Iijima is generally recognized as the first to discover carbon nanotubes, it actually seems that they have really been discovered multiple times (in fact, Iijima appears to have imaged a carbon nanotube in his thesis nearly 15 years before what is typically considered his “discovery”). It’s just that Iijima’s announcement happened to be at a time and place where the concept of a nanometer-sized cylinder of carbon atoms could both be well understood and greatly appreciated as a major focus of study. The paper linked to points out that many of the earlier studies that probably found nanotubes were mainly motivated by PREVENTING  their growth because they were linked to defects and failures in other processes. The committee could limit this by awarding the prize for the discovery of single-walled nanotubes, which brings the field of potential awardees down to Iijima and one of his colleagues and a competing group at IBM in California. This would also work because a great deal of the hype of carbon nanotubes is focused on single-walled tubes because they generally have superior properties than their multi-walled siblings and theory focuses on them.

No matter what, I would say Mildred Dresselhaus should be included in any potential nanotube prize because she has been one of the most important contributors to the theoretical understanding of carbon nanotubes since the beginning. She’s also done a lot of theoretical work on graphene, but the prize for graphene was more experimental because while theorists have been describing graphene since at least the 80s (Dresselhaus even has a special section in that same issue), no one had anything pure to work with until Geim and Novoselov started their experiments.

In 1996, another form of carbon was also recognized with the Nobel Prize in Chemistry. Rick Smalley, Robert Curl, and Harold Kroto won the prize for their discovery of buckminsterfullerene (or “buckyballs”) in 1985 and further work they did with other fullerenes and being able to the prove these did have ball-like structures. So while the prize for graphene recognized unique experimental work that could finally test theory, this prize was for an experimental result no one was expecting.   Pure carbon has been known to exist as a pure element in two forms, diamond and graphite, for a long time and no one was expecting to find another stable form. Fullerenes opened people’s minds to nanostructures and served as a practical base for the start of much nanotechnology research, which was very much in vogue after Drexler’s discussions in the 80s.

Six diagrams are shown, in two rows of three. Top left shows atoms arranged in hexagonal sheets, which are then layered on top of each other. This is graphite.

Six phases of carbon. Graphite and diamond are the two common phases we encounter in normal conditions.

So why do I think nanotubes should get the prize? One could argue it just seems transitional between buckyballs and graphene, so it would be redundant. While a lot of work using nano-enhanced materials does now focus on graphene, a great deal of this is based on previous experiments using carbon nanotubes, so the transition was scientifically important. And nanotubes still have some unique properties. The shape of a nanotube immediately brings lot of interesting applications to mind that wouldn’t come up for flat graphene or the spherical buckyballs: nano-wires, nano “test tubes”, nano pipes, nanomotors, nano-scaffolds, and more.  (Also, when describing nanotubes, it’s incredibly easy to be able to say it’s like nanometer-sized carbon fiber, but I realize that ease of generating one sentence descriptions is typically not a criterion for Nobel consideration.) The combination of these factors make nanotubes incredibly important in the history of nanotechnology and helped it transition into the critical field it is today.