Making DIY gecko tape - work in progress-----make money online

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Nathan Lefler

Guillaume Fransen

I Built It

Dustin M. Krueger

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Joel Brinton

Tyler Kragh

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Eivind Vigsnes

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today on Applied Science I'd like to

talk about my adventures in making gecko

tape if you haven't heard gecko tape is

sort of an alternative to the currently

available adhesive tapes

it actually works by a different

mechanism and it's not really a

commercial product yet but it's gotten a

lot of press in sort of popular science

articles and so it has a few attractive

qualities that make it better suited

than these commercial adhesive tapes so

first let's talk about how these

actually work each one of these tapes

has a layer of adhesive on it there's

actually a chemical on here and the

reason it's sticky is because it makes a

chemical bond with whatever you're

sticking it to and so the problem with

this is if you get it wet or if it gets

dirty the chemical becomes coated with

water or the dirt and then that the tape

is no longer sticky so if you're

constantly taking the tape off and

replacing it eventually the adhesive

will wear out and the tape is no good

anymore

the difference with gecko tape is that

this works by a mechanical method it's

actually using a different sort of

molecular bonding and so in this video

I'm going to talk about all the things

I've tried so far unfortunately it's not

working just yet but with your help

hopefully it will like the name implies

gecko tape is actually modeled after the

foot of a gecko and so part of the

reason that the geckos foot wouldn't

work with a conventional adhesive like

this is because it would quickly become

loaded with dirt and the gecko wouldn't

be able to stick and walk upside down

which is critical to its survival so the

gecko tape is sort of our answer or at

least our you know modeling of this sort

of natural phenomenon and the trick is

that the geckos foot has a whole bunch

of hairs on it and the hairs get into

very intimate contact with the foots

with the surface that the foot is

stepping on and it's these small

intermolecular bonding forces that

produce an attractive force between the

hair ends and the surface that it needs

to stick to

so most surfaces aren't perfectly flat

they're not atomically flat so if you

want to get something into very close

contact with it it needs to be very

conformable and even something soft like

this silicone rubber it's really not you

know you'd think well if the silicone

rubber has a flat surface here and we

put it down on something flat at the end

back but not really at the microscopic

level there's always going to be you

know hills and valleys and it's not

going to make really great contact so

nature's solution to this problem was to

have a structure that has very small

hairs and when you push that down onto a

surface sort of the end of each hair

will make really good contact with the

surface and then you know if you have

millions of these little hairs it's

basically almost as good as having a

solid flat piece into you know perfect

atomic contact so whereas the commercial

adhesive tapes use perhaps hydrogen

bonding or something like that where you

have this chemical adhesive layer that's

going between the tape and the surface

the gecko tape works by Van der Waals

forces which are present between all

molecules as far as I know but the trick

is that you have to get the two surfaces

really really close together like less

than you know one nanometer a few

nanometers or something it basically has

to be in contact and as I mentioned even

if you cast a perfectly flat piece of

tape and you put it on to a perfectly

flat object like this it's not even

close to good enough contact you really

need this conformable architecture so

the gecko has adapted sort of a two

layer system where it has pillars coming

off of its foot and then there's even

hairs that are a finer structure even

coming off of that and so between the

pillars and the hairs it can really

conform and have a huge amount of

surface to surface contact the actual

material itself of the hairs and the

thing that it's walking on is not

particularly important it's just the

fact that it's such in such close

contact is what makes this whole system

work so anyway so I'm really interested

in this and I searched the internet for

instructions on how to make gecko tape

or at least you know what the techniques

are being used in these research labs

and lo and behold I actually found

detailed dedicated instructions for how

to make your own gecko tape at home and

if you had part numbers for all the you

know stuff that you'd need and this is

sort of the key ingredient here so the

idea is that you make the Gecko tape by

casting the silicon rubber and it's

pretty easy you just mix it up kind of

like two-part epoxy but the the ratio is

much greater than one to one

and you pour this onto a mold and

hopefully the mold has you know holes in

it just like these these we want to form

pillars and so the mold has to have

holes in it so we're going to pour the

silicone on to that and then D mold it

and then you will have like you know

this forest of pillars coming off and

that's the structure we need to make

this whole thing work so it sounds

reasonable and the instructions are very

clever so they're going to use this

interesting membrane here too

to make our silicone cast and of course

I'll put links to all of this in the

description so definitely check that out

these are actually pretty cool this

deserves a little one minute side note

all by itself this is a track edged

membrane filter and so the idea as I

mentioned we want a whole bunch of

little holes in here so that when we

cast our silicone rubber it goes down

into the holes and we end up with this

forest of pillars so the way that you

make this track itched membrane is you

start with a really thin sheet of

polycarbonate standard you know just

just like unbreakable safety glass or

whatever and you expose it to a

radiation source I believe it's probably

a beta source but I couldn't quite find

out for sure and the trick is the beta

particles are going really fast and

they'll actually go all the way through

the polycarbonate sheet because it's so

thin we're talking 10 or 20 micron or

something like that and then you put

this into an etchant and where the beta

particles have gone through this really

thin polycarbonate sheet it's actually

weakened the chemical structure of the

plastic a little bit and the etchant

will attack only the weakened areas so

as the beta particles go screaming

through these sheets then you put this

into the etchant bath you'll end up with

a hole edge in just the places where the

particle has gone through and the longer

that you leave it in the etchant bath

the wider the holes will become because

it sort of edges from the inside of the

hole out so it's a really easy way to

get a very uniform hole size so let's

take a look at one of the what if one of

these looks like under the scanning

electron microscope this is the millah

pore membrane that was mentioned in the

instructions for making gecko tape and

it has a 5 micron hole size and it's

pretty much identical on the top and the

bottom

I also bought GE Walkman brand filters

and these have a three micron hole size

but I can tell they're built or they're

made with a different process because

the one surface is very shiny and the

other surface is very rough

so clearly the etchants that they used

to make these filters was a little

different it actually attacked the

polycarbonate a bit more so you can kind

of tell which sizes which side of the

filter was exposed to the etchant anyway

so I thought that was pretty cool what

you do according to the instructions is

you take one of these filters with the

tiny holes in it and put it down onto

some double-stick tape and then you pour

the silicon you know you mix up a batch

of silicon this is actually tin cure

silicone RTV silicone from tap plastics

and amazingly enough the silicone will

actually flow down into those five

micron holes all the way to the bottom

even so through the thickness of this

membrane and then when it cures and you

peel this off you end up with the

structure we wanted to make this you

know simulated gecko foot and it all

works the way it's supposed to but the

structure that it creates doesn't

function as well as a gecko foot in fact

it functions less well than a solid slab

of silicon as I'll show you so just to

give you a rough idea of how good the

silicone is by itself even though I

spent a lot of time saying well you know

if you put something in contact like

this even though the contact area even

though it's flat is not very good

because there'll be you know microscopic

hills and valleys it's actually pretty

good so just to give you sort of an idea

of how sticky this thing is I just sort

of stuck it down like that with almost

no pressure applied I can pull this

heavy piece of plastic around if you can

see then okay so then this is the

silicone that I made by casting the

silicone in the membrane just like it

was said in the instructions and if we

put this on here I know that it's kind

of hard to see on the camera you really

need to get a tactile sense of this no

matter how much I baby this and no

matter how careful I am the friction

coefficient with the so-called gecko

tape is way way worse in fact this is

almost sort of an anti friction material

like this is really kind of it's worse

than then just flat I mean it's

basically worse than a lot of other

things so it doesn't work and then I

started searching around on the Internet

a bit more and found someone's thesis or

dissertation where they actually

mentioned these instructions and how it

couldn't possibly work for a lot of

reasons that we're going to get into so

you know I wanted to see it first so

let's take a look with the scanning

electron microscope again at what these

pillars look like okay you can see that

yeah the casting process did work and

you can also see that the direction of

the tracks that are etched through these

plastic is not you know they're not

perpendicular to the surface they're

actually kind of all different

directions

and that's because the radiation source

doesn't just shoot out you know beta

particles in one direction they're kind

of going all different directions so

that's one problem the other problem is

that the pillars have a really high

aspect ratio they're kind of like wet

noodles just you know falling down over

there because they're too long and so I

mentioned that the thickness of this

membrane is like 10 or 20 micron or

something like that

this is one of them right here you can

see that it's really really thin in fact

it's so thin that just the static

attraction makes it really kind of

difficult to handle it's it's is thin

stuff but it's still way too thick so

the relative thickness of this thing

compared to the 5 micron you know pillar

diameter is so high that the pillar just

folds over and we don't really want it

to fold over like that what we want is

the thing to be you know fairly stiff so

then we put this down on to the surface

the pillars kind of have enough rigidity

so that the ends of the pillars touch

the surface and make a good contact

there if they're all just flopping

around then you know the whole gecko

thing doesn't work so I did a little bit

more searching and found another group

that moves instead of doing straight

pillars like this they were doing angled

kind of wiper blades almost you know

again microscopic we're talking you know

a couple microns thick or a couple

microns long and maybe a pitch of 500

nanometer and I thought well that's

pretty cool maybe there's actually a

structure that I can find kind of

around in everyday life that sort of

mirrors this because they were using

photolithography to make their parts

which I'll talk about a little later and

I came up with the idea of casting the

silicone on to really really fine metal

files so I did a little bit of research

and found out that you can get these

swiss metal files that are quite a bit

finer than the the so called american

grades of files so typically a smooth

file is the smoothest thing you can get

commonly at least you know in this

country around here if you go to your

local hardware store in the US a smooth

file is considered the final the finest

thing you can get but if you go online

to a specialty store you can get this

Swiss file and I've never seen a file

this fine this thing is really really

fine

I think the pitch is around 20 or 30

thousand inch I'll put the exact numbers

in the description

but anyway I made a whole bunch of

different castings with different files

and different viscosities of silicone

you can kind of thin the silicone and

make it into a stiffer or more flexible

stuff and you know as you might expect

the results aren't that great but they

are unidirectional surprisingly so I did

find that with a specific file pitch I

kind of have to put a little bit of

weight on the tape too to make this work

but you can kind of see in one direction

it works about that well and then in the

other direction it's not even close to

as good and the reason is that the the

teeth are you know asymmetric and when

the teeth are getting pulled sort of in

their direction they kind of fold down

and create more contact with the surface

that they're bonding to if they're going

the wrong way

when you pull them this way they just

sort of buckle and flap around and they

don't create that great contact so if

you are interested in using gecko tape

is kind of a robotic foot or grabber or

something having a unidirectional

adhesive surface is actually very nice

because you can make like a wall climber

you know gravity is always trying to

pull you down so you can make the wall

climber you know you can make the foot

basically work just the way you want so

if you put a lot

wait on it you can get Goods diction and

then to lift the foot you actually push

it upwards and it will instantly detach

because it's you know a one a one

directional gripper so after this I

realized there's no way I could get a

metal file that was fine enough to get

you know close enough contact again

another problem with the metal file is

that the teeth are sharp on the top but

unfortunately we're making a casting and

we actually want the teeth to be really

sharp in the bottom because when we do

the casting and peel it off it's

actually the tips of the casting that

are going to be interacting with our

surface and that's going to be formed by

the bottom of the of the file so you

know that basically just the

manufacturing this isn't really made for

it even though it's a good idea it was

it's not really going to work out so

then I had another great idea what about

using a CD as the former so that's

pretty cool so we're talking this thing

has a pitch between the pits and lands

with you know a few micron or something

on that order but I didn't know how deep

they were so I was able to make a

silicone cast of a CD and it is this one

so I came home one day after letting my

silicone cast there and tried it out and

I was actually really excited a it works

really well in fact way way better than

the files way better than the you know

official gecko tape instructions and

then I you know of course tried it

compared to the actual just flat cast on

glass silicone and it's it's not even

quite as good as that so so clearly

there's still some more work to be done

here the biggest problem is that the

aspect ratio of these magic pillars is

not quite right it needs to be about

four to one so if the if the spacing

between the pillars or if the size of

the pillars is on the order of 500

nanometer that means the depth has to be

2 micron and in the CDs case if it's

like a few micron in diameter then we're

going to be like maybe 4 to 8 micron

deep or something like that and so far I

haven't found any kind of easily

accessible mold that has this correct

aspect ratio and a high density of the

pillars the other problem with the track

etched membrane is that these you know

wet noodles are just spread out way too

far if you want like dense packing to

make this thing work

so all of the research groups that are

doing this are pretty much using

photolithography which involves you know

casting a photosensitive layer and you

can control the thickness of the layer

by spinning it in a spin coater and if

you'd the faster you spin it the more

you know so difficult force we get it

makes the layer thinner so that we can

control the thickness that way and then

what you do is expose your you know

micron scale pattern with ultraviolet

light and etch it away so we can

basically make little holes of almost

any width and depth that we want with

this system the problem is that I don't

have any way to print micron scale stuff

so I've done photolithography before but

I've always used a laser printers

transparency and that's there's no way

to get down to microns with that so I

need like a lensing system but then the

lenses don't pass ultraviolet light and

you know there's a lot of problems

involved so I need your help to figure

out how to pull this off there's a few

interesting ideas that well I'm sure

will come up in the comments but

basically we need to create this you

know about 500 nanometer by 2 micron

pillar and have it really dense on a

surface and something that we can cast

like silicon and then I'm pretty sure

it's going to work and we'll actually

have deco tape okay

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