Ray Baughman Long before the discovery of carbon nanotubes, Baughman proposed the possibility of new and unusual forms of carbon.
Nanotubes in a Wine Rack A wine rack (above), a hinged vase from Sicily and a toy kangaroo -- just every day objects to you and me. But for Ray Baughman, sometimes the simplest items provoke visions of nanotechnology.
12:03 PM me: hello
r.h.baughman: Hello
me: thanks for taking the time to chat with me
12:04 PM r.h.baughman: Happy to do so!
me: Could you tell me where you're chatting from?
r.h.baughman: My office at UTD. me: Could you give us a visual? What's your office like? The view from your window?
12:06 PM r.h.baughman: My view includes a Texas-style blue sky and the neighboring Engineering building.
me: sounds lovely. So I understand that you're a physicist and that you're doing a lot of work with carbon nanotubes. Is that right?
12:08 PM r.h.baughman:
I've worked in so many different areas. I don't know what to call
myself! Some people call me a physicist and others call me either a
chemist or a material scientist.
12:10 PM me:
Your web site says that you are interested in materials that have
unusual mechanical properties. I also saw the words "artificial
muscles" on the site. Can you tell me a little about that?
r.h.baughman:
Since nanotechnology is the convergence of so many different fields,
research requires interdisciplinary capabilities. Carbon nanotubes
provides areas of research, but we have a number of others.
12:11 PM me: got it.
r.h.baughman: Most materials laterally contract when stretched, like a rubber band. We investigate materials that have the rare property of expanding laterally when stretched.In fact, we have found that it is possible to switch the behavior of carbon nanotube sheets between these extremes.
12:14 PM Also,
almost all materials shrink in all directions when uniformly
compressed. We've found rare materials that actually expand in either
one or two directions when uniformly compressed.
me: wow
12:15 PM r.h.baughman: These strange properties can find application as strain amplifiers for sensors and artificial muscles.
me: okay, let me just ask a coupe of questions there. r.h.baughman: Ok.
12:17 PM me:
I can picture a rubber band and I can visualize what happens to it when
I stretch it out. The band gets longer and thinner. But you're saying
that some materials, when stretched longer, gets wider?
12:20 PM r.h.baughman:
Yes. In fact, we have found that some materials expand laterally by 15
percent when stretched only one percent. Such materials amplify the
amount of stretch by a factor of 15, which means they are strain
amplifiers.
12:21 PM me:
I want to talk about what you might use these materials for, but
first....you mentioned earlier the idea of "switching" the properties.
You said "In fact, we have found that it is possible to switch the
behavior of carbon nanotube sheets between these extremes."
what do you mean by "switch?"
12:32 PM r.h.baughman:
As we report in a recent article in "Science", nanotube sheets made by
the ancient technology of paper-making can have either negative or
positive Poisson's ratios. A positive Poisson's ratio means that the
material laterally contracts when stretched. A negative Poisson's ratio
means that the material laterally expands when stretched.
We can cause an abrupt transition between these oppostive behaviors by mixing different relative amounts of single walled and multi-walled carbon nanotubes in a nanotube sheet. The explanation is simple and can be explained using a model that is based on a collapsible wine rack, like one in my office [see the photo]. If the struts of the wine rack are rigid and the only possible deformation is by change of angle between the wine rack struts, the Poisson's ratio is positive. If the hinges are frozen and the struts are non- bendable, and the struts are allowed to expand, the Poisson's ratio becomes negative. The single walled nanotubes have a positive Poisson's ratio because they are easier to bend than to stretch. The opposite is true for the multi-walled carbon nanotubes, so they have a negative Poisson's ratio. 12:34 PM me: So, what applications do these sheets have?
12:36 PM r.h.baughman:
No problem on the photo. In fact, I can provide both a picture of the
wine rack and a three-dimensional hinged vase that I found in a
restaurant in Sicily.
12:37 PM me: not to digress, but I wonder if you see nanotube everywhere
12:40 PM r.h.baughman:
We use the carbon nanotube sheets for diverse applications:
electrochemical cells for harvesting waste thermal energy, artificial
muscles, supercapacitors, super strong/tough composites, and many other
applications.
What do you mean by "if you see nanotubes everywhere"?
12:42 PM me:
The fact that a wine rack and a hinged vase from Sicily reminds you of
the structure inherent to these materials....I mean, not many people
would make that connection. They would just see a vase. So do you see
analogies elsewhere?
1:03 PM r.h.baughman:
Sometimes the simplest articles provoke thought. For example, while
traveling in Australia I bought a toy for my son. The toy is a stuffed
kangaroo. The body portion is a big stretchy spring, and the head
rotates when the spring is stretched. This inspired our discovery of a
new type of artificial muscle that causes rotation. These new muscles
use carbon nanotube that are either left-handed or right-handed, just
like the helical spring.
In another area of our research, we know that the atoms in elemental metals are arrayed like a stack of cannonballs. Knowledge we developed for explaining negative Poisson's ratios for elemental metals lead to our prediction and observation of negative Poisson's ratios for sparce crystals, which have a density that is one thousand trillion times lower than water. In another extreme, we predict negative Poisson's ratios for ultra dense matter in white dwarfs and neutron star crystals, which are 100 billion times denser than water--both examples use this "cannonball packing of spheres" concept. 1:06 PM me: Very interesting. When did you first realize that nanotubes could be important and useful?
When in your career?
1:10 PM r.h.baughman:
Long before the discovery of carbon nanotubes, I worked on using theory
to propose the possibility of new and quite unusual forms of carbon.
The problem is the unsolved challenge of making these new forms of
carbon. When I realized that carbon nanotubes actually existed, my
research work began to focus on understanding and exploiting these
nanotubes.
1:13 PM me: What is one of the most exciting things you're working on now?
1:29 PM r.h.baughman:
One of the greatest challenges in the carbon nanotube area is in
discovering a route to carbon nanotubes of one type. Carbon nanotubes
are presently synthesized as a mixture of metallic and semiconducting
tubes having different radii. Without the ability to synthesize carbon
nanotubes having uniquely defined electronic properties, the
application of these nanotubes for nanoelectronics is problematic.
Fabrication of nanotube electronic devices presently requires sorting
through a pile of nanotubes, just like examining the individual straws
in a haystack.
We are developing a route to carbon nanotubes of one specific type, and therefore well-defined defined electronic properties. This route involves reaction of crystals to produce hydrocarbon nanotubes that are quite similar in structure to the targeted carbon nanotube. We have succeeded in this first step. The challenge now is to convert the hydrocarbon nanotubes to carbon nanotubes. I'm especially excited about another area of our research. This work, done in collaboration with Temptime Corporation, focuses on producing improved indicators that measure the accumulated effects of time and temperature on perishable products. The reaction that we use for these time/temperature indicators is the same reaction we exploit for making hydrocarbon nanotubes -- the solid-state polymerization of diacetylenes. I co-invented the concept of this type of indicator many years ago, and they are presently being used for Meals Ready to Eat (MREs) in Iraq and for ensuring the viability of vaccines distributed in remote parts of the world. PATH, a non-profit association that works with the World Health Organization (WHO), predicts that these indicators will save 140,000 lives in the next decade. More than two billion of these indicators have already been deployed for campaigns to eradicate diseases like polio. 1:32 PM me:
Are the indicators some kind of sticker? How does someone know by
looking at the indicator that the food or vaccine is no good?
1:40 PM r.h.baughman:
The indicators are stickers which are based on diacetylene powders,
which are printed like ink. As a function of the combined effects of
time and temperature, these powders turn color--thereby providing
visual indication of the extent of quality degradation of the product.
A movie briefly showing the use of our indicators to help fight the war
against polio is narrated by Brad Pitt and posted on the WHO's website.
1:42 PM me:
Very excellent. Well, I know we've been chatting a long time, so I
should let you go. But if people want to learn more about your work,
where's the best place to look?
1:43 PM r.h.baughman: More information about our work is available online, at: http://nanotech.utdallas.edu/
me: great, thanks so much for your time.
1:46 PM r.h.baughman: It's been fun to talk with you. |
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