Thread by @realscientists

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Hello everyone, I'm your host @MySci_PK and today's science story is going to be about "Gecko inspired hybrid adhesive system" 🦎

Here we go! 😁

in case you missed it, 👇here is the thread where I explained how geckos manage to crawl on ANY surface and also defy the gravity while doing so. 🤪

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in a nutshell the geckos stick to the surfaces using millions of tiny hairs on their feet and the attachment and detachment works something like this 👇

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As humans, we want to copy everything we see.

Correction: everything COOL we see.

The geckos' superpower, if I may say so, definitely falls in the COOOOL category!

So off the humans went in the search of a material similar to gecko's foot.

I mean, at this point the focus must have been on NOT capturing geckos, giving them pedicures and then borrow their feet.

3 important factors while hunting for a material resembling gecko's foot:

1. has to be flexible
2. easy to handle
3. easy to clean (cause you know, no one wants to spend hours cleaning in the lab 🤪)

Ceramics - Not flexible
Metals - Difficult to clean
Most materials - Difficult to handle

The only category left is - POLYMERS! 😁

Humans looked for several options. I mean there are tons of polymers options out there.

They narrowed down to this one special polymer called Polydimethylsiloxane (PDMS).

The name sounds scary, I know. 😊

Here is the structure of PDMS.

Does this help? 😊

Okay, probably the name and the chemical structure scared you off.

Please come back, I have got a pretty picture of PDMS for ya! 😉

pic is a screenshot from Elveflow website.

PDMS is flexible, easy to handle and easy to clean.

Also resembles the gecko foot hair.

We got a match! 😁

Now let us proceed with making the hairy foot in the lab! 😉

Now if you remember, the gecko foot hair were really TINY.

Next challenege : to make TINY structures out of PDMS. 🧐

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Steps for making PDMS tiny hair

1. make a mold
2. pour semi-ready PDMS in the mold
3. let the PDMS become ready
4. remove from the mold

and TADDAAAA, PDMS hair are ready!

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Now I am well aware that the structures in the above picture 👆look less like TINY hair and more like pillars.

We decided to make microstructures instead of nanostructures. And now I will tell you why.

PS: don't take this 👇gif personally. 🤣

Remember when I told you I am going to be speaking about "gecko-inspired-hybrid adhesive system"? 😊

We didn't just make a gecko-foot, we went a step ahead and made it better! 🤠🤓

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We coated one side of each of these pillars with Gold.

The thermal expansion coefficients of PDMS is 20 times larger than gold.

This means that the gold-coated side will be stiffer compared to the bare-PDMS side.

This especially important when the temperature is increased from room temp. to 40°C.

At room temp, the pillars stand straight.

But as soon as the temperature starts increasing, the PDMS starts expanding.

During this time the gold coated side of the pillar is stiff in which case the expanding PDMS tried to overpower (read: bend) the pillar.

At room temperature when the pillars were straight, the tips fo the pillars had good contact with the surface.

BUT as soon as the temp rises, the pillar bends and the contact is lost - > adhesion lost. 🤓

So finally we have "thermally controlled gecko-inspired-hybrid adhesive system"

This was my work as a summer intern at the Leibniz Institute of New Materials, Saarbruecken, Germany.

The idea came from my supervisor's brain with me doing the groundwork! 🤠😉

I hope you all enjoyed and learned something new from the science story! 😍

If you have any questions, please, feel free to ask me here (until tomorrow) or on my private account (@MySci_PK). 😊

Thank you for sticking till the end! 😁

*The End*