How a liquid lens works (electrowetting)--- make money online

that's actually pretty cool Ivan tried

this before I haven't had this power

supply for too long so I'm not really

sure what it's capable hey everyone

in a previous video I showed a little

bit about a liquid lens so this is a

device that has some water and oil

trapped in a capsule and when you apply

power to the capsule it the water

droplet changes shape and changes the

focal length of the lens so in this

video I'm going to show you a little bit

more about the fundamental concepts that

are involved in a liquid lens and why

the thing actually works so here I've

set up a little test rig this is just a

piece of aluminum angle bracket or

aluminum square stock and I've coded the

top of it with teflon tape so this is

five thousandths of an inch thick and

it's actually adhesive I'm not sure how

they got the adhesive to stick to the

Teflon itself but this stuff you know it

works just sort of like scotch tape but

it's Teflon on the top and I covered the

whole top of the aluminum with the

Teflon and then I have this small

electrode sort of poking down into a

droplet of salt water it's just regular

table salt salt water I don't know what

the concentration is just sort of random

and the electrode is connected up to my

high voltage supply here so this is a

low current high voltage supply and when

I turn the voltage up the droplet

changes shape and what's interesting is

I can disconnect the electrode from the

supply and the droplet stays in the same

shape until I short the electrode out

and then when I plug it back in it

changes shape again when I take this out

it still stays in the same shape until I

short it so the little droplet of water

is actually acting like a small

capacitor as well as providing this this

liquid lens effect so let me show you

why this actually works okay so here's a

cutaway view of what we're looking at so

here's the aluminum base plate then

there's a thin layer of Teflon and then

there's a water droplet on top of the

Teflon so normally the surface of the

Teflon here is hydrophobic meaning that

the water molecules are not very

attracted chemically to the surface of

it so what happens is the water much

more preferentially clumps to

self then clumps to the Teflon surface

and we end up with this water beating up

so when you've seen the car ads with you

know the special car wax or whatever

they talk about water beating up and

there that's the reason for that is that

the water much more prefers to stick to

itself than the surface so things like

wax and oil and Teflon are hydrophobic

and cause the water to beat up so in

that state this is sort of a simplified

diagram what we talk about is the

contact angle which is the angle that's

made between the surface and the tangent

formed by the the droplet angle coming

in here so let's just say this is 120

degrees about or whatever and it's just

the angle here to the tangent line drawn

to the water droplet now if we apply a

power to this system what we can do is

put an electrode on the aluminum and put

an electrode in the water and I should

add that the water is conductive we

hadn't we need to add something to the

water to make it conductive salt some

electrolyte any electrolyte and if we

put some voltage on here

let's just just for reference I was

using about five kilovolts and the

reason that the voltage has to be kind

of high is because the thickness of the

teflon tape is fairly thick this is five

thousandth of an inch thick and for

commercially made liquid lenses this

might only be ten microns or even a

hundred microns or something like that

but much thinner than the tape that I'm

using and the thing that actually

effects how the water drop is going to

change size is the electric field

between it and the aluminum so making

this distance smaller or making the

voltage greater will achieve essentially

the same thing so when we put power on

it the water is actually attracted

there's an electrostatic attraction

between the water molecules and the

aluminum down here and the reason for

that is that h2o is a polar molecule and

when you put power or when you when you

put an electric field on the water these

water molecules will actually be

preferentially pulled down towards the

aluminum and also pulled

out towards the aluminum so if you're a

water molecule sitting right here you

feel a traction pulling down to the

aluminum when there is an electric field

applied here and eventually the water

droplet will take on this shape so here

the contact angle is let's say 70

degrees whatever that is and it changes

the shape of the whole droplet because

those water molecules are basically

being pushed down attracted downward

toward the aluminum so there's one more

addition that we can make to make this a

little bit more useful in the liquid

lens situation the problem with having

just a drop of water hanging out on the

surface is that if you tilt this thing

sideways I mean if you have a lens and

it's in a camera and you're moving the

camera around eventually gravity will

want to tug on this drop of water and

change the shape without you wanting to

change shape so what we can do is encase

the drop of water in oil and we're going

to use an oil that's exactly the same

density as water and the oil is

hydrophobic and also has a different

index of refraction in terms of optical

properties than the water so this

interface between the droplet of water

and the oil surrounding it will create a

lens and since the oil is the same

density as the water if we turn this

whole thing around in space gravity

won't preferentially pull that drop of

water out of shape so we have this this

top piece actually I shouldn't have

drawn this with a meniscus on here this

is actually sort of like a glass window

that seals this whole capsule off so

this is a flat piece of glass up here

and for a lens we obviously couldn't use

a thick piece of aluminum down here

either so for a real liquid lens this

bottom part would also be native glass

and our electrodes would have to be very

carefully designed in order to make the

droplet work it looks sort of like this

so here's a crude cutaway view of how a

liquid lens might be built so we have a

glass window on the bottom and a glass

window on the top one electrode goes

through into the water which is down

here and it's surrounded by oil and the

other electrode goes to a piece of the

metal

case that is behind a Teflon insulator

so by applying the power or the voltage

across these two electrodes the contact

angle at this point will change and we

have a similar situation with a contact

angle is what changes the size of the

droplet so here the contact angle will

be changed and then that changes the

shape of this meniscus so instead of

having a curvature like this we might be

able to make it flat or we might be able

to make it bow the other way so liquid

lenses can change from no power to

negative power to positive power so if

you don't believe me when I say that

water is attracted in an electrostatic

field check this out I've got the high

voltage supply is set to maybe eight or

nine kV and when I bring the electrode

close to the stream of water that's

coming out of the tap here you can see

that it's quite attracted me I crank it

up a little bit a little over 10 kV now

and I've got the other side of the power

supply a Tec attached to the water pipe

so the electrostatic field is going

between the column of water and the

electrode if you don't have access to a

high voltage supply you can also

generate high electrostatic fields with

the old comb on cloth trick so just by

physically rubbing this together we're

stripping electrons from one of these

materials and depositing them in the

other so if I charge up this comb and

then bring it near the column of water

you can see the electrostatic attraction

there and you can tell from the 15kv

setting on my supply I've probably got

more than 15 kilo volts on this comb

right now just just by how close this is

getting at how much it's causing the

water stream to deflect it's a pretty

cool demo I should also point out

there's no it doesn't the polarity

doesn't matter so if the comb is

positive and the water stream is

negative there will be exactly the same

effect achieved if the polarities were

reversed so the reason that there is

attraction and that it doesn't depend on

the polarity of the electrostatic field

applied is because each of the little

water

cules has a positive end and a negative

end and it doesn't really matter there's

no overall positive or negative charge

associated with the water molecules so

when I bring a charged object near the

water stream let's say the comb is

positive if I bring this positively

charged object towards the water stream

all the water molecules that are flowing

down in the water column will rotate

such that their negative end is toward

the comb in their positive end is

further away so if all the molecules in

here have their negative end toward the

comb and their positive end further away

just because the molecules themselves

are polarized then there will be a net

force generated because all of the

negative ends are toward the comb and

all the positive ends are away and

opposite charges attract so think of it

as if you were trying to attract a

compass needle and you brought a magnet

near the compass needle the needle would

rotate around so that the end of the

needle that's attracted to the magnet is

toward the magnet and the end isn't

attracted is further away so there will

be a net force a translational force

that actually tries to pull the needle

towards the magnet okay I hope that was

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