Self-Healing Material

This is a self-healing polymer. It's not sticky but it does stick to itself!

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[SteveMould]

"Two by two, hands of blue"

[ruebancastro]

'I can't put metal back together.' then cuts metal and tries to put it back together. Scientific method at work. I love you Steve, make it tangible for us all.

[loganh]

"Cold welding" totally blew my mind, and learning about it made it much easier to understand how a similar effect is possible here on earth. Awesome video!

[Giraffemini]

Asking the question "Why DONT things heal or stick back" is such a great explainatory tool here! I wish some of my teachers had that way of explaining stuff back in the day.

[Silly]

This material repairs itself better than I can repair my life

[Isolanporzellator]

A part of our group happens to be working on exactly such polymers, so I am somewhat familiar with the topic. There are 3 main ways to get self-healing polymers (sorted from least likely to most likely to explain this polymer):

1) Simply using a highly elastic resin, which causes stress to deform the material rather than break actual bonds. Over time and sometimes with a bit of heating the original shape is restored. An example of this being used is the "scratch shield", which is a highly elastic clearcoat used by Nissan to give their car finish the ability to heal moderate scratches by itself. Clearly your material has bonds fully broken upon tearing, so this is not the technique that's being used here.


3) Reversible bond breaking and formation (Also called "Intrinsic self-healing"). Polymers of this type have specific functional groups that can connect and disconnect with corresponding groups in a reversible manner. After a tear, rejoining the ends causes loose chains to reconnect to each other, healing the polymer. Closed chains can also be opened and then rejoined to form new links.
There are numerous ways to achieve this, some examples include:
3a) Reversible formation of covalent bonds, for example via reactions (DOI: 10.1126/science.1065879). Some chemical bonds can be reversibly broken and reformed. After joining the ends together, chains in both ends can break apart and recombine with chains from the other end, reestablishing covalent links. Usually, energetic triggers like heating or UV-light are required to facilitate the mending process. You did not use any such triggers, so this is probably not what you have.
3b) Reversible supramolecular bonding. I am quite certain that this is what makes your polymer mendable at room temperature. There are several interactions that can cause polymer chains to stick to each other without any covalent bonding (ionic attraction, coordinative bonds, hydrogen bonds and π-stacking interactions). These can sometimes also be broken and reestablished at room temperature.
You can imagine these supramolecular polymer networks to be like ball and stick magnet toys for children. Your sticks are short polymer chains with negative endgroups (ionic groups or chelating Lewis bases) and your balls are positive metal ions. The combination of both can form large networks of interconnected or entangled chains. The sticks can be flexible, but are not broken apart easily. However, the forces connecting balls and sticks are much weaker and so these connections can be rearranged with a relatively low activation energy, causing the material to stick to itself easily even after being fully disconnected for a long time.

An interesting example of an elastic polymer that sticks to itself but not other stuff is Parafilm, which is just a mixture of polyethylene and wax. It can't truly "self-heal", but it goes to show that even much simpler polymeric systems can show some of these properties.


I just wasted an hour of my time to write this... oh well.

[SunderMun]

At Uni I did a project on self-healing materials, taking inspiration from Mussels. We were trying to replicate the self-healing properties by making an organometallic aerogel. Was really interesting but the scope ended up becoming multiple PhD thesises (no idea how it ended, if it has yet)

[rebecacedeno]

I think the mechanism that puts the pieces back together is supramolecular interactions. The polimer chains are functionalized, at their ends there is an additional bonding, like a puzzle piece. So when you put them back together the puzzle pieces at the end of the polymer chains meet the other puzzle piece.

[teo_lp]

I may have experienced a self-glueing sticker once. This vid left me thinking if it was something similar. It was in an airport, a self-service baggage drop-off station automatically printed the long paper strip that you attach as a tag to your bag, with its identifying information. I remember the tag had one printed paper side, and another plasticky side that surprisingly didn't stick to your hands but glued firmly to itself when you bent it around the handle of your bag and made it touch itself. I remember being baffled that it didn't feel like the familiar adhesive side of a sticker at all. It didn't stick to the handle of your bag either which made it really convenient to detach later without leaving residue. Has ayone else ever come across this?

[miriamrosemary]

Thanks for explaining why things that are broken apart and not sticky don't self-heal/weld! I never knew that!
And also that polymer seems really cool and probably has tons of applications :)

[collinandersen]

You don’t know how long I’ve been wondering why metals don’t self heal. I asked this to one of my metallurgy professors and he acted like I had asked a stupid question and blew me off. Thanks for finally scratching this irritating itch!

[liandoaethend]

This teaches better than the chemistry class in my school

[isadorah]

I used to always ask myself as a kid why cut things can't be put back together. Then I graduated at Chemistry but never realized how obvious it is LOL
Prob because I work with water so no time to think about materials anymore. Thank you for pointing it out!
This self-healing polymer is indeed very interesting

[dwo]

It is so awesome that you anticipated the question of what would happen in a vacuum when discussing cutting a metal.
It was the first thing that popped into my mind and I'm so thankful I didn't have to ask or look it up.
Thanks!

[randomstuffloool]

Props for the cameraman for going monucle size and recording the split

[Rappid_]

i have no clue what this man is saying but also understand it all in perfect detail

[petergoestohollywood]

“Cold welding” doesn’t actually have to happen in the vacuum of space. From experience I know that if you polish two quartz glass plates very flat and smooth and then stick them together, they will permanently bond as well. It’s pretty awesome!

[JohnBaleshiski]

Love your humor of putting up a Patrick Stewart (fixed) shrine. You are fantastic. Thanks for regularly making us smarter.

[GogiRegion]

I know this is another example of a sticky thing, but another self adhering polymer that people see in everyday life is gluten. To simplify it a bit, gluten proteins have long amino acid chains that can link together both end to end to make the chains longer (the primary purpose of kneading dough), as well as side chains with thiols that when hydrated can bond to each other so the chains connect. When both of those interconnect a lot, it creates sheets of connected parallel protein chains.

[canadiankazz]

Where were you when I was failing high school chemistry?! You explained things much better than my teacher ever did.