DIANNA COWERN: This episode is sponsored by audible.
Welcome to the science.
Have you seen this experiment before,
with the milk and the food coloring?
And then you put some dish soap on the end of a Q-tip,
and you dip it in the middle of the liquid
to get this awesome experiment.
This is the kind of experiment that never gets old.
But if you're like me, and you fidget a lot
and you keep playing with it, you'll
notice that if you flick the Q-tip
across the surface of the water, you get these little beads that
roll across.
They're like little bowling balls
that roll across-- oh, my god.
That's so pretty.
I have to take a picture.
Thanks to some phantom high speed footage from
"BeyondSlowMotion"-- awesome channel,
definitely check it out, link is in the description--
you can see that these beads form as strings of milk break
up into individual droplets and then bounce on the surface.
It's so mesmerizing.
But what are they?
I drove myself crazy, googling every different combination
of soap and milk and food coloring and liquid.
And I could not figure out what they are.
So I did what I always do when I need to know something.
And I asked my physics friend, Dan Walsh,
who immediately said--
Antibubbles.
I thought he was joking.
You think I'm joking.
Turns out he was close.
Anitbubbles are even cooler than this.
DIANNA COWERN: Dan, are you ready for this?
I was born ready.
Oh!
DIANNA COWERN: Ah, yeah!
That's amazing!
I am here with Ashley who's my intern,
and Dan who is my friend.
And he's just really enthusiastic about physics.
Also s PhD student in physics.
That's another reason why I'm so interested.
Yeah.
Also a student of physics.
So much physics here!
So antibubble is the exotic sounding name
given to these little spheres that we've made underwater.
Because they're kind of like the opposite of a regular bubble.
A regular bubble is a thin film of a liquid, enclosing a gas
and then typically floating in a gas, like air.
Whereas an antibubble is a thin film of gas,
enclosing a sphere of liquid and then typically fully submerged
in a liquid.
ASHLEY: Do you want to try this one?
Oh, yeah.
Just try and bunch of different parameters.
DIANNA COWERN: So you've got to put water
in both of these containers, then add soap, mix it all in.
And then you squeeze water from this container
onto the surface of this one.
Oh, that was a good one.
ASHLEY: You got some good ones.
DIANNA COWERN: Those are awesome.
The water drags some air along with it,
which closes off into a shell.
DAN: It takes some time to get used to it.
DIANNA COWERN: It is like a sweet spot angle.
You have to find a sweet spot.
But it's easy to see the structure of the antibubbles
when we added food coloring into the squeeze bottle.
Because then when they pop, you can
see that colored liquid come out, typically making
the shape of a vortex ring.
ASHLEY: Oh!
DAN: Did you see how there was a little regular bubble that
came up?
DIANNA COWERN: By using high speed cameras,
physicists have observed that the air
at the bottom of the antibubble floats to the top,
popping the air film.
You've now got a little air droplet
that floats to the surface, which is just
the opposite of a popped bubble, where the liquid film falls
because of gravity.
Thank you guys!
Sure, thank you.
High fives.
[LAUGHTER]
So despite sounding like some exotic form of matter,
antibubbles are actually just as common as regular bubbles.
You make them when you wash your hands with soapy water.
But they pop much more easily than regular bubbles.
Why?
Wait, so why do regular bubbles pop?
So you form a regular bubble by decreasing
the surface tension of water.
And when you decrease the surface tension,
bubbles can live a lot longer.
There's actually a really interesting molecular reason
why bubbles keep their nice spherical shape.
It works like this.
Each soap molecule has a hydrophilic,
that is a water-attracting head, and a hydrophobic-- or a water
repelling-- tail.
When you make a soap bubble, the soap molecules
line up so that hydrophobic heads
are in contact with the water.
They have a slight electric charge,
which means that the soap molecules on one
surface of the film repel the soap
molecules on the other surfaces, which
helps keep the film from collapsing in on itself.
That is, until the film evaporates.
Now an antibubble, on the other hand,
is also made of soapy water.
But there are a few key differences.
Everything's all flipped around.
So in the antibubble air film, the hydrophobic tails
are now facing each other in the film.
And the hydrophilic heads are facing away in the liquid.
Soapy water is actually a good electrical conductor,
which means that electric charges can flow easily
through it.
So those slightly charged hydrophilic heads
attract oppositely charged molecules in the water,
basically neutralizing the charge of the surface
of the antibubble air film.
Those electric repulsive forces that
basically help the bubble keep its shape
don't exist in antibubbles.
And so they pop much more easily than their regular bubble
cousins.
No!
So as you can see, they're kind of hard to make.
Like, we struggled with a lot of the steps.
Don't put too much food coloring.
Yeah.
DAN: I would suggest practicing without food coloring first.
Because otherwise you're going to make all the fluid read.
DIANNA COWERN: Yeah.
The other trick is that if you add some corn
syrup into this bottle, you'll increase
the density of this liquid-- because corn syrup is more
dense than water-- so that you can
get your antibubbles to sink.
Or even get a little bit of the corn syrup
in here, mixed in the bottom, so that you've
got a gradient of density from more dense to less dense.
Then when you squeeze this liquid into the cup,
you could get them to float right in the middle, kind
of like a neutral buoyancy in that level
of the liquid density.
It takes a lot of patience.
They're so cool!
I love science.
So if you were to make an antibubble in space, where
there is no buoyant forces caused by gravity,
you could make the antibubble last a lot longer.
Destin over at "Smarter Every Day"
is making a video with more about this.
So as soon as that's up, I'll put
the link in the description.
Even after all this explanation, there's
still a lot we don't really understand about antibubbles.
So stay tuned for the research on this
and potential applications.
But in the meantime, I did find out you
can make antibubbles in beer.
So cheers to anti-suds.
Happy physics sudsing.
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