Lecture 28: Organic Glasses - Polymers

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Let's get started. Settle down. The weekend has not quite started. Let's look at what happened on Wednesday. There are the scores. Class average about 67, standard deviation about 17, so that means it is a bell curve sitting right on the 50.

A lot of people improved. There were a lot of rags to riches stories, but there are still a fair number of people down here. And so my suggestion to you is that if you are down here and you want to -- Too much talking, people.

If you want to start your weekend soon, I will help you by inviting you to leave. You don't have to stay here if you don't want to, but if you do choose to stay, please sit in silence. This is 3.091.

If you are down here, get in and see us. Please talk to your recitation instructor, come on in and see me, and we will talk about strategies for studying, strategies for success. I want you to pass this class, but just doing the same thing over -- This is, I think, Einstein's definition of insanity, doing the same thing over and over again expecting a different outcome.

If what you have been doing up to now is not working, let's try something else. And we can help you. The model solutions are up and, if there are changes that need to be made, please get in to see me.

Why don't we agree not to do it until Monday. I would like you to first talk to your recitation instructor and make sure that there is something worth exploring. The final exam is on the 15th of December.

The final exam is going to essentially represent the equivalent of a double monthly test. You will have three hours. But I give about double the amount of work, so it should give you enough time to finish.

But the final exam will consist of a mix of what is covered since Test 3. It is like a Test 4 monthly. And also some material going all the way back to the beginning of the semester. It is both cumulative and focused, so it has breadth and depth.

And it is really good to pass the final. If people pass the final, it tilts things in favor of passing the class. If you crash and burn on the final, it raises a lot of questions as to whether you have been working all along, you gave up around Veteran's Day and so on.

I urge you to keep at it. And don't leave everything to the last minute. If you take a look at your final exam schedule, this is the third day of the final exam period. Some of you may have exams Monday and Tuesday.

If you think you are going to cram it all in on Tuesday night, it is not going to work. You are going to be very tired by the middle of that week. You need to have a plan. You have to work incrementally so that things sink in.

You cannot just do high-speed Fick's second law and expect it is all just going to go zooming in. It won't. It will look like first law. It will go in this side and out the other side. Keep at it.

Well, let's get on with the lesson. Today is going to be a chance to apply the organic chemistry that we learned on Monday. I said we learned enough organic chemistry to set the stage for polymers, so today we are going to talk about polymers.

Monday we will come back and finish up polymers, and then that will lead us into biochemistry. This is all part of applied organic chemistry. To date, what are the types of solids that we have seen in 3.091? We saw solids that are consisting of single atoms stacked.

Then we saw compounds stacked. Last day we started looking at chains. And we have even seen networks, some of them amorphous, some of them crystalline. Today what we are going to look at is a new form of solid where the building block is a long chain, long in quotation marks.

And this is a polymer. Polymers are pervasive in our society. We see them in everything from your CDs, the CD cases. You see them in trash bags. You see them in clothing, microfibers. Some of these new fibers have an incredible mix of properties in terms of comfort and security.

Auto parts. All over the map. And, when it comes to soft matter, we, as human beings are solid state devices. Mother Nature is a polymer chemist. It is all macromolecular chemistry. If we want to introduce polymers today, let's have an operating definition.

A polymer is a long chain molecule with a repeating chemical structure. And let me give you an example. I will give you one that builds on something we saw the other day. We have seen ethylene or ethene.

This is C2H4, and it has the chemical structure. What we can do is turn this into a long chain molecule with a repeating chemical structure in the following manner. We can react it with something that will catalyze the destruction of this double bond.

And once this double bond is broken we can flip it over to the other side of the carbon giving us the opportunity to continue to link. This is done with a radical, so we can denote the radical R. And I am going to put this, remember, the unpaired electron.

This is a radical with its unpaired electron which we term an initiator. And so this initiator, when it meets something with a double bond, reacts. The double bond is something that could be turned into two single bonds.

Let's go to maximize bonds. This one has no bond, broken. This one has a double bond. We could react the two and result in the following, and now this goes over to here. Now the initiator has attacked this double bond, built the bridge, and now the radical is at the end here.

Well, ethylene is a gas. If this is sitting in a reactor, gas molecules are colliding with this, so now we can attack another ethylene and so on. You get the picture. Eventually this thing is thousands and thousands of atoms long.

Let's do one more. And now we will have the bond here, one, two, three, four, like so. And so now you see a repeat unit. Here is a repeat unit. And this repeat unit can go n times where n is very, very large.

N can be on the order of ten thousand or so giving us molecules that have atomic masses of a million grams per mole. These are huge. We call this n. I am using n now in a new way. N is called the polymerization index and it represents the number of repeats of the mer unit.

The mer is the repeat unit. And what is the length of this thing? Let's get a sense of this. Suppose we had something that was, say, ten thousand units long. Let's say n is ten thousand, that might give me something on the order of about a million grams per mole.

Let me do the calculation a different way. Suppose I had something that had an atomic mass of a hundred thousand grams per mole. This is the atomic mass of the polymer. And divide that by the atomic mass of ethylene.

Ethylene is 28 grams per mole. This is the mass of C2H4 and this is the mass of the polyethylene, one molecule. That would give us then a polymerization index of 3,571, about 3,600. And, if we estimate a carbon-carbon bond distance, about one and a half angstroms for carbon-carbon bond distance, that gives us something that is on the order of about a half a micron in length for one molecule.

And to give you a sense of what that really means, I want to show you a demo here. What I have is a pull chain that you use downstairs in grandma's house to turn on the lights. This is a whole bunch of these brass balls that are held together by metal.

Let's have each of these represent carbon. And this one is about three thousand units long, about 40 feet. There are about three thousand of these units here. Let's get a sense of how big this is.

This is one molecule. Imagine what happens when this, in the melt state, is flowing. What happens when the melt decreases in temperature and this attempts to solidify? What are the chances that this is going to come out in one of the 14 Bravais lattices? It is vanishingly small.

I feel like I just came back from New Orleans. I didn't even have to lift my shirt. Look at all this stuff I have. This is terrific. That is one molecule. And, if we imagine what happens, let's say that it is pretty clear that, let's call this macromolecule, solid macromolecules favor being amorphous.

Favor the amorphous state. This is a notion of pure crystallization. And we can imagine, for example, all of the rules that we learned for the inorganic glasses, the silicates apply to organic glasses.

Let's look at, say, volume versus temperature for something like polyethylene. I am just going to call this PE, polyethylene for short. We can imagine we are up here in the melt state, we cool down, we go through a normal melting point and then we reach a solidification at some glass transition temperature.

Let's say this is at a slow cooling rate, so this is Tg slow. And maybe on another occasion we cool at a fast rate, and so we will have a different glass transition temperature and it will be higher.

And let's say this over here is room temperature. What do I find? I have two different volumes. You have seen this before. If I have for constant mass equal masses. The one with the higher volume has the lower density.

This should be low-density. Let me just put the fast cooling rate. Fast cool. This is slow cool. This will be low-density polyethylene formed here and this will be high-density polyethylene simply by the different rates of cooling.

Constant mass means then that you have density is mass over volume, so the one with the higher volume gives us the lower mass. We can see how by different processing we have the ability to change between high-density and low-density polyethylene as a function of the cooling rate.

Now, other things can happen. If we go at a low rate of cooling, we can get even down here at very, very low cooling rates. We might even get some degree of crystallization. Could we switch over to the document camera feed, please? Let's see what happens when this thing attempts to crystallize.

Here we are. What can happen is if we cool at a slow enough rate, this cannot form a single crystal but what it can do is fold back on itself and, thereby, put these atoms into a regular arrangement.

This is now forming a zone of crystallinity. And why is it doing this? It is doing this to maximize Van der Waals bonding here. The tighter it packs, the greater the intensity of bond formation. We see this happening in the formation of such zones of crystallinity.

And when this happens we have a change in properties. Let's consider low-density polyethylene. Well, we know that this thing is going to be mechanically flexible. It is going to be flexible because what are the only bonds operative here? They are just weak Van der Waals bonds, mechanically flexible.

It is high band-gap material and it is amorphous. There are no grains, there are no grain boundaries so it is transparent because of the high band-gap and it is clear. We can see through it because there are no internal surfaces.

That is low-density polyethylene. High-density polyethylene, well, it has some zones of this. The high-density polyethylene has these near crystalline zones, and then it is broadly amorphous. The difference here is small.

The density here is about 0.92 grams per centimeter cubed, and this is about 0.96 grams per centimeter cubed. There is a little bit of tighter packing here. But what happens when we get into these zones of regularity, because there is a higher atom density, this turns out to have a higher reactivity with light.

Therefore, I am using n here not to mean index of polymerization. This is index of refraction. The index of refraction in the near crystalline zones is not equal to the index of refraction in the amorphous zones.

Now we have zones that are near crystalline in zones that are amorphous. And so we have the effect of internal interface. And, as a result, the high-density polyethylene is opaque. These zones here add rigidity.

There is a stiffness here. This one is rigid. What do we have? We have low-density polyethylene. This is what you see in use in food wrap. Whereas, this is what you see in the milk jugs, the milk jugs that are somewhat hardened and do not admit light.

They are both the same material, but what has happened is just a slight change in the strength of the material through a change in processing, a change in cooling rate. Let's look at how we can take this idea of tailoring properties and extend it more broadly and maybe put it on a firmer footing.

Let's look at the various items in our toolbox. We want to tailor the properties. The first thing we can do is control composition. Control of composition - that is purity. We can start with pure polymers and polymers that are made of combinations of different polymers.

Let's start with the pure polymer. The pure polymer, because it comes from a different heritage, have their own terminology. Pure polymers or polymers consisting of a single mer are called homopolymers.

They consist of a single mer, one mer type, and it is repeated. For example, polyethylene. Ethylene is the repeat unit. And that is all you see. Polyethylene from end to end. Then if we want to mix different mers, we get what is to a polymer what we would call an alloy in a metal system.

And this is called a copolymer. It has more than one type. Greater than one mer type. And so, for example, we could make a copolymer of, say, polyethylene with, say, polyvinylchloride. Polyethylene and polyvinylchloride.

And, this notation, this lower case c with the hyphens on either side indicate that we are talking about a copolymer of these two units. You know what the parent unit is of ethylene, I have shown you that.

And we saw last day that if we took ethylene, dropped a hydrogen, this became the vinyl radical. And then, if we put a chlorine here, this is vinyl chloride. It has a double bond here. We can use the same polymerization technique, propagate this by converting it to a single bond.

And now, instead of vinyl chloride, we will have the polymer polyvinylchloride. And, if we had both vinyl chloride in the reactor and ethylene in the reactor, we would be grabbing molecules of both types and attaching them.

So, as you move down the chain, you might have ethylene unit, vinyl chloride unit, ethylene unit and so on. And, if we could go to the computer feed, I can show some examples of different ways in which we can put these on the chain.

The first one, this is taken right from your reading, is called the random copolymer where A and B represent different mer units. A could be ethylene and B could be vinyl chloride. And here they are just random.

You get some unit of vinyl chloride and then several units and so on. And some people want this for particular mechanical properties, so let's document these different types. If we have random arrangement of the mer groups, random arrangement of mer types, we have what is called the random copolymer.

Let's just use this same example. This could be polyethylene lower case r-PVC. That tells you it is a random copolymer. The next one shows what they are calling a regular copolymer where you have alternating.

It is strict alternating arrangement of mer-type. It moves from one to the other in alternating sequence. And this is known as the alternating copolymer to distinguish it. You cannot call it regular because "r" is already taken for the random copolymer.

The third one is shown up here where we take and cluster the different mer types. Instead of having alternating one to the other, we take a run of one type of mer and then a run of another type of mer.

This is a clustered arrangement of mer types into what we call these clusters, are called blocks of the same type of mer. And such a material is called a block copolymer, which is shown up here where you see there are four units of A and then four units of B and then two units of A, four units of B.

This is a little bit unrealistic. Typically, commercial block copolymers are usually diblocks or triblocks. If it were a diblock of polyethylene, it would be one run of polyethylene and one run of polyvinylchloride and that is it.

You don't do this sort of thing but the artist got carried away and somebody didn't proofread. And the last thing you can do is the one on the bottom which is called the graft. The graft is sort of a type of block copolymer where what you have is graft of one mer type in the form of a side chain onto another mer type for the backbone.

You cluster them but you cluster them very deliberately in this manner, and that is shown in the bottom one. The backbone is all As and the side chain is all Bs. And here is one. Some of you are going to be doing some traveling so I have put up a very common one.

This is ABS, acrylonitrile-butadiene-styrene. You have seen butadiene. We say that last day, styrene. What this is, the backbone is all butadiene, and then the side chains are alternately acrylonitrile and styrene.

And this is what is used for hard sided luggage and also this. All these old telephones are made of this graft copolymer. And, by playing with the nature of these side chains, we can obviously make this so that it is somewhat flexible, or we could make it so that it is rather rigid.

Again, examples of architecture at the local level dictating properties. We have these examples of how we can tailor the properties. The second thing is the configurations of the side groups. Side group configuration.

These are all options that we have. And we exercise them in the synthesis, by playing with the synthesis conditions and also the catalysts that are present. And that is shown here. There are basically three ways you can put the side groups on.

The upper one shows the methyl group randomly going. Sometimes it is above, sometimes it is below, and there seems to be no pattern. This whole notion of side group configuration is referred to as tacticity.

It means the placement of the side groups. There are only three choices here. Either you put them all on the same side of the chain, that is the bottom one, isotactic, or you put them on alternate.

One sits on one side of the chain then it is on the other side of the chain. You alternate back and forth with regularity. That is syndiotactic. And then the third case is, come what may, there is no seeming plan, and that is the atactic.

Those are the three types that you need to be aware of, isotactic, syndiotactic and atactic. And you can figure those out. Iso obviously means they are all on the same side of the chain. Atactic is as amoral, apolitical, so this is random.

And then by elimination this must be alternating. And I think on the next one I did a little doodling for you. Just to bring home what is going on, the first one at the top is atactic polypropylene.

So you see there is propylene. And what has happened is this double bond has been broken and now it can propagate. And this methyl group in some cases is above and in some cases below the chain. Here is polystyrene.

This is vinyl benzene or phenylethene or styrene. And this double bond is broken and you have these phenyl groups hanging off the side. And this is just vinyl chloride which we saw over here. Again, seeing the synthesis.

Then the last thing we can look at is backbone architecture or chain architecture. Chain here referring to the main chain. And this falls under the general term of conformality. And we are going to revisit this when we talk about proteins.

It is very important in biological systems. And it is a direct result of this, which I showed you last day, that this bond is free to rotate. And, if it rotates in certain ways so that all the side groups line up perfectly, you end up with this so-called eclipsed version.

If you look at the chain on the very end you would see one dot that represents the backbone. Actually, it is zigzagging. You would see the edge of the zigzag. And then all of the pendant groups will be lined up in front of one another and you would see nothing except the very first one.

That is the eclipse and that is the most regular, straight line. And this is staggered where it rotates where it wishes. And I showed you this one where this is hardly something with the polymerization index of 3600.

But it starts giving you the sense of some are more nearly straight and some are very heavily coiled. Both of these are still called straight chains, but there are some things that we can look at. First we have the linear one, the linear chain molecule.

And so that is one. Furthermore, if you look here, there is some fine structure. You may even see that at some point along here there is even some attempt at crystallization. But, even so, the system moves in one direction from one end to another.

The alternative is branched chain. It is a different type of architecture. In that case, you actually have something that - This is not graft. This is actually the main component of the backbone continuing to grow but growing in a plurality of paths.

You can imagine that one of these is going to pack much better than the other. One is going to have a greater chance of forming such zones of crystallinity. Clearly, it is going to be the linear chain.

These branches stick out and they prevent tight packing. The branched chain is harder to crystallize. And, when it forms its amorphous structures, it has more free volume. And also you can think about the glass transition temperature, Tg, how is that going to work and so on.

By looking at the branching you end up with such structures. There is one other one, and that is shown here. That is to take several chains, whether they are linear or branched. I am just going to draw several straight chains here.

And it is possible to link chains by joining them with some covalent bridges. This is a covalent bridge, this is a covalent bridge, and it actually links one chain to another. And imagine the mechanical properties of this material.

Otherwise, there would be weak Van der Waals bonds. And, if we apply a shear stress, we can cause the material to plastically deform. But these are strong covalent bonds. What will happen is I can move this material, shear it up to a point, but then I would encounter the resistance of these bonds.

And, as soon as I let go of the applied force, it springs back. By cross-linking, this is a cross-linked architecture, I impart some elasticity. And this is, in fact, the structure of rubber. And we call such polymers elastomers because they will spring back to shape.

And what would have to happen here in order to allow for the cross-links? We have to be able to form covalent bonds. If we are going to form covalent bonds, we have to break some bonds that are present in the backbone.

If I have bonds such as this in the backbone, and then I come up with this R group that wants to somehow attach, it is pretty clear that if I break one of these bonds in order to make the attachment, I cut the chain.

It is axiomatic then, if I am going to form cross-links, I need to find a position along the backbone that has a double bond. Thereby, I can break the double bond, convert it to a single bond, link up with the cross-linking bridge and keep the integrity of the backbone while forming a new bond to an adjacent chain.

This is the condition for which we form elastomers and this is the basis for rubber. And I think this next cartoon shows that - here is polyisoprene. And you can see there is a double bond in the backbone.

And by presenting sulfur, sulfur is capable, as is oxygen, of forming bridges. We saw in the silicates, in the borates how the oxygen forms covalent bonds on either side, thereby linking silicate units.

Well, sulfur is below oxygen. If we believe Mendeleev, it should have similar properties. And so sulfur is forming bridging structures breaking these double bonds and now linking the one orange backbone with the adjacent orange backbone.

Sulfur enables cross-linking. And this, in fact, is discovered here in Boston. It was Nathaniel Hawthorne **Nathaniel Hayward** who was working in Roxbury and was trying to stabilize rubber. Natural rubber is very sticky, and so he found that by adding sulfur he could cause the rubber to lose its stickiness and thereby develop a synthetic rubber that had superior properties.

And then it was Charles Goodyear who came to Boston, saw this, took the invention and licensed it. It was Goodyear who accidently spilled some of this cross-linked rubber onto a hot stove. And the thermal treatment gave a far superior rubber which gave birth to vulcanization.

And then from there it is all history of automobile tires and whatnot. This is advantageous from a property standpoint. But it is very disadvantageous from the standpoint of recycling. How could one possibly recycle this material? Let's compare these two.

Let's compare the case of polyethylene. Polyethylene consists of many chains and they will interpenetrate and entangle. What are the bonds between these chains? The bonds between these chains are Van der Waals.

This is a Van der Waals solid. These are Van der Waals bonds. And we know Van der Waals bonds are operative at low temperatures but not operative at high temperatures. If we take polyethylene and heat it, these bonds will weaken and this will turn liquid.

And we can reprocess this. By going to high temperature it can reprocess because we are only breaking these weak Van der Waals bonds. Now, if we take this cross-linked polyisoprene, I will show it in this manner, how are we going to reprocess this? If we begin to heat this, we are going to have to go to an extremely high temperature because we have to break covalent bonds.

If we go to a temperature high enough to break these bonds, if we go to a temperature high enough to break the backbone, we go to thermal destruction of the entire material. So such materials cannot be reprocessed by heating.

These are called thermoset. And thermoset are very difficult to process, difficult to recycle. You might say, well, you don't have to just do it by thermally reprocessing. Why don't you use some kind of a chemistry? Go in there with chemistry that will attack these bonds.

These are strong covalent bonds. What kind of a solvent is going to be strong enough to snip those bonds? It is going to be a very aggressive solvent. And what are the health effects of the use of that solvent? Do you want to bet the company on the use of that and find out later that you have class action lawsuits using such chemicals? This is the issue when you drive down the highway and see these mountains of spent automobile tires, how to recycle them.

This is the issue. Whereas, over here, you heat this up and you can redo it. Such materials are called thermoplastic. They can be reprocessed or rendered plastic by a temperature rise. They are environmentally much, much easier to process.

Afew more things here with the polyethylene. This shows what I was just doing on the document camera. This is the partially crystallized polyethylene and this is what it looks like in these zones.

You do not have all of the chains lining up, but if you look at the atoms on end you will see there is the C2H4 unit. And the C2H4 units are lined up. And, sure enough, what is the basis unit here? It looks orthorhombic, as you would expect.

The molecule that has the aspect ratio of 2:1 you expect is going to come out in one of the Bravais lattices that also has some anisotropy associated with it. And here is some x-ray diffraction data.

This is the diffraction of a fully crystalline polymer. If we took a short length polyethylene and cooled it very slowly or took it out of a solvent, we would end up with something that is totally crystalline.

And we see we have discrete peaks. Here it is the same material amorphous. And, if it is a little bit painful to look at this because it is reminiscent of a question on the recent test, this is what the data show.

By looking at this mixed spectrum, you can get a measure of the extent of crystallization, by looking at the relative intensity of the peaks versus this broad single peak which is associated with the first nearest neighbors, because in ethylene we know that carbon has hydrogens as its nearest neighbors and so on.

This works just as well as the free volume as a measure of the degree of crystallization. So, we see this. The last thing I want to touch upon is the polymer synthesis, just to put that into a formal setting.

I have already shown you addition polymerization, which involves the use of a radical or catalyst-assisted. And it is characterized by three stages where I showed you the initiation in which we generate the radical.

Then there is the growth of the polymer until we get to the length of chain that we want. Then, finally, the extinguishing of the reaction called termination. What is really going on here is in the initiation stage we create the radical.

Here the growth is simply the polymerization. Polymerize, or if you like attachment. And then over here is to quench the radical. And those are the stages that are involved. All we are really looking at here is monomer attachment.

And, in this case, the composition of the polymer is equal to the composition of the mer unit. The composition of the polymer is simply identical to the composition of the mer unit. We simply use the radical to catalyze, and that is the only effect.

But there is one other way to form, and this is called a condensation polymerization. And it works a little bit differently. It involves more than one mer type. I am going to show this as mer type number one, which has associated with it a terminal hydrogen.

And mer number two that has associated with it a terminal hydroxyl. And condensation polymerization works to attach the hydroxyl to the terminal hydrogen to form a covalent bond between the residual R1 and R2 and expels water vapor.

These reactions are conducted at temperatures above 100 degrees C. This is expelled. And ultimately is captured as a condensate. Oddly enough, condensation polymerization, which involves the stepwise building of the polymer by reaction between two different mer types and expulsion of water vapor condensate is named not for what it is but for the byproduct that is not part of it.

This is the prototypical reaction. Clearly here you keep losing water. In this case, the composition differs and the final mass of polymer is not equal to the composition of the mer groups. And the mass is less than the sum of the masses of all of the mer groups because we keep losing water.

I think here we have some examples of the various materials. This, again, is taken from your reading. Here is a suite of addition polymers, many of these you encounter in everyday life. I have been talking about polyethylene.

If we replace the hydrogens with fluorines, we get PTFE which you know by the trade name Teflon. Polypropylene. Polystyrene which you have seen in these clamshells. Not so much today in coffee cups for their insulating capability.

Polyacrylonitrile is a fabric Orlon. PVC is that white tubing that you see used in plumbing facilities. Polymethylmethacrylate, many of you are wearing eyeglasses that are made of this material. This is Plexiglas or Lucite.

And so on. And down here even some of the rubbers. On the other hand, here are the condensation polymers. And notably are the nylons, which are made by condensation polymerization. And I have put a little bit of fine structure on here.

You can look at this on the website. The bond that will link the R1 to R2 is called the amide bond. This is the amide bond. And so nylons are known generically as polyamides. And, furthermore, there is on end that has the carboxylic acid end, and then the other end which has the amino end.

And, as you go down, you see Kevlar is here, which you know is used as a substitute for steel belting in tires, also used as the fiber in bulletproof vests. Some fabrics here, Dacron and Mylar, various polyesters.

The polycarbonates. This rigid phenyl group here is what gives the polycarbonates their high strength. This is Lexan which is used in jet engine windshields and is also used in sports goggles to give you the resistance against impact and so on.

These are made by this process, and we are going to see this process again when we talk about protein synthesis because Mother Nature works by condensation polymerization. There are many similarities between the nylons and the proteins that make up our bodies.

What I would like to do in the last five minutes is talk about an example of the use of block copolymers in energy. And some research that has been going on here at MIT for about ten years now looking at new materials to make superior batteries, batteries for the wireless age.

And these are the kinds of batteries that exist today in terms of the amount of energy they store per charge. And you see lead acid, which is abundant and cheap, is actually quite low in terms of how much energy it stores.

And what is in your cell phone and your laptop is the lithium ion battery which is 150 watt hours per kilogram by this metric. And, in fact, it was the advent of the nickel metal hydride battery that enabled the laptop computer.

All of the components were in place in the 1980s, but sodium sulfur is a molten salt batter. It operates at 300 degrees C so that was not very popular for laptop use. The only thing that was available was down here NiCd.

And people were not going to release laptops that had a runtime of about one hour. But with the advent of nickel metal hydride it all of a sudden became sensible to put out such devices. And now we have a lithium ion.

And, ironically, as the capacity of the battery has risen, the appliances that go on the laptop have risen. And so the runtime does not change because each next generation has a more intense power hog of a CPU.

You want a DVD, you want a fancy screen and so on. All of that is consuming energy. But if you knew how to power it down and run it minimally, you would find that you could get run times of six, seven hours.

The approach that we used here was to use block copolymers. And we used block copolymers such that we wanted to get a solid. You see, people think of batteries as these cylindrical devices that are very heavy, but we had a different image.

We thought that this should be the battery. The battery should remind us of something like this, and this is called dreaming. This is a potato chip bag. You think it is just nothing by a lowly potato chip bag.

Open it up sometime. What do you find? You see it is a multilayer laminate of polymer and metal, because the potato chip is precious. You have to protect it against spoilage. It can spoil by becoming soggy from humidity or it can become rancid from oxidation.

You need the polymer to protect it from one and the metal to protect it from the other. But this tells me that you can make a multilayer thin film laminate very cheaply. If this polymer could be made into a lithium ion conductor, we would have a solid state battery.

Instead of aluminum, we would put lithium. Instead of this polymer, we would put something that could conduct lithium ions. And then we would put the cathode on here. Now we have something that is solid state.

It is very light. And it has a property that no other battery has. You can reshape it. You can wear it. You can put it in the body of a car. You could change the watch band to change the battery.

If you can think conceptually, you can do different things. That is how it began. And with my colleague Professor Anne Mayes who started a program to look at a class of materials, block copolymers that were chosen in such a way to give lithium ion conduction at room temperature.

Solids are very poor ionic conductors. Most solids that you know that conduct ions only operate at high temperatures. The oxygen sensor in your car does not work for about the first 15 minutes. When the car is cold, the oxygen sensor is getting garbage for a signal.

It has to heat up. But we don't want a battery that runs at 300 degrees C. At least I don't. There are selection rules here that went into play. And, ultimately, we built something that looked like this, that has a methacrylate backbone and different side groups that could solvate lithium ions, and we made the materials and ultimately made first generation batteries that are thin film, mechanically flexible.

And the choice of electrode materials provided its lithium-based chemistry and so on allow us to go forward. And it was by using the principles shown here on these boards that we were able to engineer a polymer that could have the mechanical properties of something like Saran wrap but have the electrical properties of sulfuric acid in your lead acid battery.

That was the paradox, how to engineer those seemingly irreconcilable properties. Right there, control of local structure. And I have all this stuff up here that we don't have time to go through, but let me show you where you can go when you get something that is really nice.

Look at this. This is flexible solar cell. This is silicon on a polymer substrate, so it is collecting photons and converting them into electrons. And then you take something like this and put it on the back of a flexible solar cell.

And then you put on the front of this the LEDs. You put this up in the roof, you collect the photons, and then afterwards you get the photons back. Now that is change. Learn your chemistry. Have a nice weekend.

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