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Polyfluorene-Wrapped Carbon Nanotubes Decorated with Photocleavable Side-Chains

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Alex Adronov discusses the cleavage on the polyfluorene-SWNT complex via UV-Vis-NIR absorption spectroscopy.

Image courtesy of interviewee. December 21, 2023

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This video video text discusses carbon nanotubes, which are nanoscale tubes made entirely of carbon. They have unique properties, including high strength, flexibility, and electrical conductivity, making them valuable for various applications. The speaker focuses on single-walled carbon nanotubes and their challenge of aggregation, likening them to sticky caramel. To enhance their solubility and usability, the nanotubes are coated with conjugated polymers that can improve dispersion but can also impede electrical conductivity due to insulating side chains.

To address this, the speaker describes recent research involving cleavable side chains. By using a trigger to remove these side chains, the nanotubes can come closer together, increasing conductivity. The study explores different methods for inducing this cleavage, including photochemical and thermal approaches. Although the thermal method proved effective with reasonable processing temperatures, it was slow. The most recent advancements involve using a chemically cleavable side chain that significantly increases conductivity within seconds, allowing for practical demonstrations where a circuit lights up upon treatment.

The overarching goal is to develop thin, transparent, and conductive films for flexible applications, such as displays and smart textiles that can harness solar energy. These advancements in carbon nanotube technology could lead to innovative products, including flexible displays and smart materials for diagnostics and energy harvesting.

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Here are some key quotes extracted from the video about carbon nanotubes and their applications:

1. **Introduction to Carbon Nanotubes:**
- "Carbon nanotubes are these really interesting materials."
- "They're nanoscale tubes... made up entirely of carbon."

2. **Properties of Carbon Nanotubes:**
- "These structures have lots of really interesting properties."
- "They have high strength... but they are quite flexible on the full length scale."
- "The unique property of carbon nanotubes is that they're conductive as well."

3. **Challenges in Working with Carbon Nanotubes:**
- "One of the challenges with carbon nanotubes is that they like to stick to one another."
- "They're very insoluble, and therefore we can't do very much with them."
- "Directly reacting with the carbon... diminishes their conductivity properties and also their strength properties."

4. **Functionalization and Solubility:**
- "We want to wrap them with something... a conjugated polymer."
- "This coating on the surface of that carbon nanotube will enhance the solubility."

5. **Methodology for Improving Conductivity:**
- "The problem is that those side chains that we introduced to impart solubility are also insulating."
- "By introducing a trigger, we can cleave those side chains... and allow the carbon nanotubes to come closer together."

6. **Advancements in Conductivity:**
- "We showed that if we heat a film of these wrapped carbon nanotubes... we see that the side chains do come off."
- "In one instance, we used a photochemical cleavable linker... but that was challenging because the carbon nanotubes are black."

7. **Current Research and Future Applications:**
- "We've recently submitted a paper... where we use a chemically cleavable side chain... the process happens within seconds."
- "We can generate these films that are highly conductive, very flexible."
- "Imagine if the screen was itself, the display that could be rolled up."
- "We are hoping that we'll get conductivities that are high enough that we can make a film very thin and transparent."

These quotes encapsulate the introduction, properties, challenges, methodologies, and future perspectives regarding carbon nanotubes in materials science and technology.

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X-TIMESTAMP-MAP:LOCAL=00:00:00.000,MPEGTS=900000

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Just as a, as a brief background, carbon nanotubes are,

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are these really interesting materials.

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They're nanoscale, tubes, as the name implies,

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they're made up, entirely of carbon.

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And, there's structures is really interesting.

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I actually have like a, a sort of 3D printed model of, of,

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you know, just an example of one of these things.

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And you can imagine this, this is a very short segment,

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but it, it becomes very, very long.

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Um, and, it's, as I said, entirely made up of carbon.

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That's sp two hybridized.

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So it's like benzene rings all fused together.

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Uh, and these, structures have lots

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of really interesting properties.

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So I'll just show a, a slightly different depiction

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that I have on a, on a side.

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So you can have these structures be, single walled

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or multi walled.

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And in my group, we mostly work

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with single walled carbon additives.

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And their properties are really interesting in

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that they have, high strength.

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So it is hard to break one of these structures

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because, there are many

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strong carbon carbon bonds

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folding the full structure together.

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Uh, but they are quite flexible on the full length scale.

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If you take just a small segment like the, the model

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that I have here, they, they could be very rigid,

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but when you think about them from the perspective of say,

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a long human hair, on a short length scale,

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it could be quite rigid.

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But on the full scale, it's, it's quite flexible

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and it can be knotted and, and things like that.

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It is very similar with carbon nanotubes,

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but the unique property of carbon nanotubes is

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that they're conducted as well.

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And so they can, serve

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as either semiconducting materials

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or metallic, carbon nanotubes

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that are made commercially are mixture of both types.

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And in my group, we're interested in,

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exploiting those conductivity properties

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and also trying to purify their semiconducting or metallic

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and, and make use of their, of their properties.

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One of the challenges with carbon ude is that they like

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to stick to one another.

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Uh, and I, I was thinking of an analogy

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and you can think about, you know, some,

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like a candy like caramel, caramels.

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Uh, if you think little bits of caramel

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and stick them all together, they all stick to one another.

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But to prevent that, we put a wrapper around them, right?

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And similarly with carbon tudes, they like to stick

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to one another, and these very large structures become very

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difficult to work with for a chemist.

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They're very insoluble, and

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therefore we can't do very much with them.

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And so what people have, tried to do is to,

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functionalize them in, do chemical reactions on the surface

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of the carbon nanotube that will introduce, tructure

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that hang off their surface,

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that will improve their solu, for example.

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But the problem with directly reacting with the carbon is

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that, by doing that we, ruin the perfect structure,

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the, the lattice of the carbon, atoms,

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and we diminish their conductivity properties

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and also their strength properties.

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And so rather than doing direct attachment, we do similar to

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what we do with candies, we wanna wrap them with something.

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And the thing that we wrap them

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with is a conjugated polymer.

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And here i, I, I show a depiction

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of conjugated polymers here,

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just the back, one of the polymers.

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And these are all like fused aromatic, rings

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or benzene rings that are linked together.

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And these structures will, interact with the surface

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of a carbon nanotube,

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and similar to the candy, they'll wrap the carbon nanotube.

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And so produce a coating on the surface of that,

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carbon nanotube that will enhance the solubility.

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And that solubility comes from the fact

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that conjugated polymers, have

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the aromatic backbone,

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but they also have side chains,

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that we introduce on these structures,

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that imparts solubility to these polymers

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because the polymers themselves are also not very soluble,

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but with these side chains, they become soluble.

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And so we're interested in exploiting these,

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carbon nanotubes that are wrapped with polymers,

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for a variety of applications.

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Okay. So we can now,

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introduce these polymers on the surface of the nanotubes.

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We can get that nano tube polymer complex

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to disperse in the solvent.

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It becomes much more soluble.

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And so then what we, want

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to do is say, make a film on a substrate

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or, use, put these carbon es down

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between electrodes

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and look at their conductivity properties.

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But there we, we have a problem,

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and that's really where the papers

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that we're talking about kind of, come into play.

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Uh, the problem is that those side chains that we introduced

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to impart solubility are also insulating.

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They are not conductive,

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and they prevent the carbon nanotubes from coming into close

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contact with one another.

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And you need close contact in order to impart so,

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conductivity to the, overall structure.

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So we make a film of these carbon nanotubes that are coated,

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that are wrapped, and we find

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that the conductivity is really poor, right?

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We, we don't get much conductivity in that film.

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And so we thought, well, we need those side chains

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to be present for solubility,

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but wouldn't it be great if we could just get rid

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of the side chains

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and allow the carbon anes to come to closer contact

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and remove all that insulating material around them.

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And so the idea here is one that's shown in,

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in this slide where what we

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have is a carbon nanotube that's wrapped with these,

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polymers that have izing side chains on them.

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But what we want to do is introduce a cleavable linker here,

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okay, for the side chains.

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And so by introducing a trigger,

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we can cleave those side chains, leave the linker

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and release the side chains to allow them to come off of

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that polymer and, and be released.

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And so we have done this now with several different,

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approaches to those cleavable linkers.

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So in one instance,

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we used a photochemical cleavable linker.

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So we shine light and we cleve the linkage.

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We cleve a bond, and that allows the side cheek to come off.

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But what we found was that that was a bit challenging

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because if we want to do that

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cleavage in a film in a solid state, well,

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the carbon nanotubes are black,

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so they don't allow light penetration.

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If we make that thick film to, to,

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maximize conductivity, we can't get the light

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through the film in order to cleve all the side chains.

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We can do it in solution.

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And we demonstrated that,

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in solvent under the new conditions, we can shine light

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and remove those side chains.

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But in a solid state, it doesn't work very well.

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And so then we also thought about using a thermally

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cleavable linker, and that works quite well

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because all we have to do there is heat the, film up

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to some temperature.

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And we had a linker

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that was cleavable at about 170 degrees Celsius.

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That sounds like it's, it's pretty hot,

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but that's not too bad in terms of processing conditions

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for say, electronics.

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Um, and so we showed that if we eat a film

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of these wrapped carbon nanotubes

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that have the cleavable side chains, over time

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we see that the side chains do come off.

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So the, the linkage breaks, the side chains,

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come out and we see a conductivity increase.

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But what was interesting was that with

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that thermally cleavable system,

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it was a little bit disappointing in

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that it took a long time for the conductivity

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to start to increase.

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Um, after we, while we were heating,

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it took about seven hours for us to start

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to see an increase in conductivity,

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and it plateau at about 17

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or 18 hours of eating at 170 degrees.

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So we were happy in that we kind of proved the concept,

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in that study.

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But the overall, process was very slow.

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And we think that that's because

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although the linkages holding the side chains,

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on the polymer cleave quickly,

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the side chains themselves are not very volatile.

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So it takes them time to come, come out of the film

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and evaporate off.

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And then after that evaporation, the carbon nude need

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to reorient or reorganize to, form the linkages

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or new linkages to allow conductivity to increase.

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So that all took many hours.

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Uh, but the, the process of work,

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the other limitation in the initial study was

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that the overall conductivity was quite low.

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And so we, we've been working more recently on,

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trying to improve both the rate of this cleavage,

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and increase in conductivity

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and also the absolute value of

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that conductivity to, to go up.

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And so we've recently submitted a paper, I, I don't,

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I can't talk in too much detail about this paper

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because it's not published yet,

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but we recently submitted a paper

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where we use a chemically fieldable side chain,

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where we introduced a certain, molecular trigger

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that cleaves a side chain,

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and the process happens within seconds.

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So side chains come off very quickly,

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and the conductivity

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that we're observing is about forwarders

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of magnitude higher than the original, studies.

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So now we're able to, actually make a little circuit

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with a, with a light connected to a battery that's connected

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to one of our carbon ude films.

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And before we dip it into our solution of,

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of the trigger molecule, it's completely non-conductive.

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So the light doesn't turn on, but

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after we dip it into our trigger molecule, all

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of a sudden the light comes on.

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So we can, generate these films

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that are highly conductive, very flexible,

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and we're still working on improving

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the overall conductivity as much as we can.

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When we make a film of carbon nanotubes, if we, you know,

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expose it to solvent, we don't want that film once it's made

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to come off, right?

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So we want to have something

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that is easily processable at first.

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We can make a film,

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we can potentially pattern it on a surface

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between electrodes

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or in whatever, arrangement that we want,

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but then when we add the trigger, we want

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that film to be locked in.

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We don't want it to be removable, very easily.

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So by removing those side chains, we,

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we achieve the increase in conductivity

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and also the stability of that film.

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One of the things that I'm, I keep thinking about is trying

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to make these films so

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that they're really thin and transparent.

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So we're not there yet.

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We, in order to get the conductivities that we need

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for a light bulb to, to turn on, we,

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need a fairly thick film, and it's not very transparent.

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But as we improve our process

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and improve the, composition

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of metallic carbon nanotubes, we're working on,

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on selectively, dispersing metallic carbon tudes

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with their polymers, we are hoping

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that we'll get conductivities that are high enough

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that we can make a film very thin and transparent,

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And then we can place it on a flexible

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substrate, for example.

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And so that opens up all kinds of display applications

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where the display is truly flexible,

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where you could roll it out.

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So, you know, I like to talk to students about, the fact

12:08.285 --> 12:10.525
that when we, when we give presentations,

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we have a projector that projects onto a screen

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that you pull down from the wall.

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Well, imagine if the screen was itself, the display

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that could be rolled up,

12:19.865 --> 12:21.285
and you don't need the projector,

12:21.305 --> 12:24.285
you would just pull down the screen, connect

12:24.285 --> 12:26.925
to it wirelessly, it would light up, would be missive,

12:27.105 --> 12:28.565
and then when you're done, you just roll

12:28.565 --> 12:29.605
it up and put it away.

12:29.825 --> 12:30.885
So that, that kind

12:30.885 --> 12:32.845
of application would be, would be pretty neat.

12:32.845 --> 12:35.165
But there are all kinds of interesting applications

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for transparent, conductive, flexible materials.

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You can think about coding textiles

12:41.005 --> 12:45.245
and having, electrified sort of textiles where

12:45.795 --> 12:48.525
they, they could act, say, photovoltaics

12:48.545 --> 12:51.845
and charge your phone as you're walking around outside just

12:51.845 --> 12:53.525
by light hitting your, your garment.

12:54.025 --> 12:57.365
Um, or all sorts of sensor applications

12:57.625 --> 12:59.005
for diagnostic medicine.

12:59.465 --> 13:02.885
All these things require, well, in,

13:02.905 --> 13:07.845
in some cases they require flexible, conductors

13:08.355 --> 13:11.325
that respond to deformation, let's say.

13:11.505 --> 13:15.005
So we, we we're working on, these thin films

13:15.075 --> 13:18.445
that are on sort of rubbery substrates, whereas

13:19.385 --> 13:21.005
the substrate stretches

13:21.145 --> 13:24.485
or bends, you get a difference in conductivity

13:24.545 --> 13:27.005
and you can detect that, that sort

13:27.005 --> 13:28.365
of force being applied on.

00:00 - Just as a, as a brief background, carbon nanotubes are, are these really interesting materials. They're nanoscale, tubes, as the name implies, they're made up, entirely of carbon. And, there's structures is really interesting. I actually have like a, a sort of 3D printed model of, of,

00:19 - you know, just an example of one of these things. And you can imagine this, this is a very short segment, but it, it becomes very, very long. and, it's, as I said, entirely made up of carbon. That's sp two hybridized. So it's like benzene rings all fused together. and these, structures have lots of really interesting properties. So I'll just show a, a slightly different depiction that I have on a, on a side.

00:48 - So you can have these structures be, single walled or multi walled. And in my group, we mostly work with single walled carbon additives. And their properties are really interesting in that they have, high strength. So it is hard to break one of these structures because, there are many strong carbon carbon bonds folding the full structure together.

01:11 - but they are quite flexible on the full length scale. If you take just a small segment like the, the model that I have here, they, they could be very rigid, but when you think about them from the perspective of say, a long human hair, on a short length scale, it could be quite rigid. But on the full scale, it's, it's quite flexible and it can be knotted and, and things like that. It is very similar with carbon nanotubes, but the unique property of carbon nanotubes is

01:37 - that they're conducted as well. And so they can, serve as either semiconducting materials or metallic, carbon nanotubes that are made commercially are mixture of both types. And in my group, we're interested in, exploiting those conductivity properties and also trying to purify their semiconducting or metallic and, and make use of their, of their properties. One of the challenges with carbon ude is that they like

02:06 - to stick to one another. and I, I was thinking of an analogy and you can think about, you know, some, like a candy like caramel, caramels. if you think little bits of caramel and stick them all together, they all stick to one another. But to prevent that, we put a wrapper around them, right? And similarly with carbon tudes, they like to stick to one another, and these very large structures become very difficult to work with for a chemist.

02:32 - They're very insoluble, and therefore we can't do very much with them. And so what people have, tried to do is to, functionalize them in, do chemical reactions on the surface of the carbon nanotube that will introduce, tructure that hang off their surface, that will improve their solu, for example. But the problem with directly reacting with the carbon is that, by doing that we, ruin the perfect structure, the, the lattice of the carbon, atoms,

03:06 - and we diminish their conductivity properties and also their strength properties. And so rather than doing direct attachment, we do similar to what we do with candies, we wanna wrap them with something. And the thing that we wrap them with is a conjugated polymer. And here i, I, I show a depiction of conjugated polymers here, just the back, one of the polymers. And these are all like fused aromatic, rings

03:33 - or benzene rings that are linked together. And these structures will, interact with the surface of a carbon nanotube, and similar to the candy, they'll wrap the carbon nanotube. And so produce a coating on the surface of that, carbon nanotube that will enhance the solubility. And that solubility comes from the fact that conjugated polymers, have the aromatic backbone, but they also have side chains,

04:05 - that we introduce on these structures, that imparts solubility to these polymers because the polymers themselves are also not very soluble, but with these side chains, they become soluble. And so we're interested in exploiting these, carbon nanotubes that are wrapped with polymers, for a variety of applications. Okay. So we can now, introduce these polymers on the surface of the nanotubes. We can get that nano tube polymer complex

04:41 - to disperse in the solvent. It becomes much more soluble. And so then what we, want to do is say, make a film on a substrate or, use, put these carbon es down between electrodes and look at their conductivity properties. But there we, we have a problem, and that's really where the papers that we're talking about kind of, come into play.

05:09 - the problem is that those side chains that we introduced to impart solubility are also insulating. They are not conductive, and they prevent the carbon nanotubes from coming into close contact with one another. And you need close contact in order to impart so, conductivity to the, overall structure. So we make a film of these carbon nanotubes that are coated, that are wrapped, and we find that the conductivity is really poor, right?

05:33 - We, we don't get much conductivity in that film. And so we thought, well, we need those side chains to be present for solubility, but wouldn't it be great if we could just get rid of the side chains and allow the carbon anes to come to closer contact and remove all that insulating material around them. And so the idea here is one that's shown in, in this slide where what we have is a carbon nanotube that's wrapped with these,

06:04 - polymers that have izing side chains on them. But what we want to do is introduce a cleavable linker here, okay, for the side chains. And so by introducing a trigger, we can cleave those side chains, leave the linker and release the side chains to allow them to come off of that polymer and, and be released. And so we have done this now with several different, approaches to those cleavable linkers. So in one instance,

06:38 - we used a photochemical cleavable linker. So we shine light and we cleve the linkage. We cleve a bond, and that allows the side cheek to come off. But what we found was that that was a bit challenging because if we want to do that cleavage in a film in a solid state, well, the carbon nanotubes are black, so they don't allow light penetration. If we make that thick film to, to, maximize conductivity, we can't get the light

07:07 - through the film in order to cleve all the side chains. We can do it in solution. And we demonstrated that, in solvent under the new conditions, we can shine light and remove those side chains. But in a solid state, it doesn't work very well. And so then we also thought about using a thermally cleavable linker, and that works quite well because all we have to do there is heat the, film up to some temperature.

07:35 - And we had a linker that was cleavable at about 170 degrees Celsius. That sounds like it's, it's pretty hot, but that's not too bad in terms of processing conditions for say, electronics. and so we showed that if we eat a film of these wrapped carbon nanotubes that have the cleavable side chains, over time we see that the side chains do come off. So the, the linkage breaks, the side chains,

08:07 - come out and we see a conductivity increase. But what was interesting was that with that thermally cleavable system, it was a little bit disappointing in that it took a long time for the conductivity to start to increase. after we, while we were heating, it took about seven hours for us to start to see an increase in conductivity, and it plateau at about 17

08:30 - or 18 hours of eating at 170 degrees. So we were happy in that we kind of proved the concept, in that study. But the overall, process was very slow. And we think that that's because although the linkages holding the side chains, on the polymer cleave quickly, the side chains themselves are not very volatile. So it takes them time to come, come out of the film and evaporate off.

08:57 - And then after that evaporation, the carbon nude need to reorient or reorganize to, form the linkages or new linkages to allow conductivity to increase. So that all took many hours. but the, the process of work, the other limitation in the initial study was that the overall conductivity was quite low. And so we, we've been working more recently on, trying to improve both the rate of this cleavage, and increase in conductivity

09:31 - and also the absolute value of that conductivity to, to go up. And so we've recently submitted a paper, I, I don't, I can't talk in too much detail about this paper because it's not published yet, but we recently submitted a paper where we use a chemically fieldable side chain, where we introduced a certain, molecular trigger that cleaves a side chain, and the process happens within seconds.

09:57 - So side chains come off very quickly, and the conductivity that we're observing is about forwarders of magnitude higher than the original, studies. So now we're able to, actually make a little circuit with a, with a light connected to a battery that's connected to one of our carbon ude films. And before we dip it into our solution of, of the trigger molecule, it's completely non-conductive. So the light doesn't turn on, but

10:24 - after we dip it into our trigger molecule, all of a sudden the light comes on. So we can, generate these films that are highly conductive, very flexible, and we're still working on improving the overall conductivity as much as we can. When we make a film of carbon nanotubes, if we, you know, expose it to solvent, we don't want that film once it's made to come off, right? So we want to have something

10:52 - that is easily processable at first. We can make a film, we can potentially pattern it on a surface between electrodes or in whatever, arrangement that we want, but then when we add the trigger, we want that film to be locked in. We don't want it to be removable, very easily. So by removing those side chains, we, we achieve the increase in conductivity

11:13 - and also the stability of that film. One of the things that I'm, I keep thinking about is trying to make these films so that they're really thin and transparent. So we're not there yet. We, in order to get the conductivities that we need for a light bulb to, to turn on, we, need a fairly thick film, and it's not very transparent. But as we improve our process and improve the, composition

11:38 - of metallic carbon nanotubes, we're working on, on selectively, dispersing metallic carbon tudes with their polymers, we are hoping that we'll get conductivities that are high enough that we can make a film very thin and transparent, And then we can place it on a flexible substrate, for example. And so that opens up all kinds of display applications where the display is truly flexible, where you could roll it out.

12:04 - So, you know, I like to talk to students about, the fact that when we, when we give presentations, we have a projector that projects onto a screen that you pull down from the wall. Well, imagine if the screen was itself, the display that could be rolled up, and you don't need the projector, you would just pull down the screen, connect to it wirelessly, it would light up, would be missive, and then when you're done, you just roll

12:28 - it up and put it away. So that, that kind of application would be, would be pretty neat. But there are all kinds of interesting applications for transparent, conductive, flexible materials. You can think about coding textiles and having, electrified sort of textiles where they, they could act, say, photovoltaics and charge your phone as you're walking around outside just by light hitting your, your garment.

12:54 - or all sorts of sensor applications for diagnostic medicine. All these things require, well, in, in some cases they require flexible, conductors that respond to deformation, let's say. So we, we we're working on, these thin films that are on sort of rubbery substrates, whereas the substrate stretches or bends, you get a difference in conductivity and you can detect that, that sort

13:27 - of force being applied on.

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