2 buckets full of colored water?
2 willing subjects?
A slow mo camera?
Let’s do this.
But wait… why is only one of them getting soaked?
The chemistry behind this is pretty darn cool.
So cool in fact that we got the 2016 Chemistry Champions winner,
Dr. Mallory Hinks, to help us out in this video.
Raincoats, car windshields, waterproof phones.
雨衣 汽车挡风玻璃 防水电话
They all use a little chemistry to stay dry.
To show how this works,
we sprayed a Reactions team member with an industrial strength waterproof spray,
or what’s called a superhydrophobic coating.
“Hydrophobic”meaning water-fearing or water-hating
and”super”meaning ”a whole lot”
Ah, quick safety note guys: spray the shirt.
So what IS happening?
Well, it turns out, this spray works by borrowing a waterproof tip from nature.
Check out this leaf hopper’s wing.
Or this lotus leaf.
These surfaces repel water so well that a drop is just going
to sit on top of them as a ball that’s pretty close to a spherical shape.
See, if water drops on a flat surface like a table,
it flattens out into a mini puddle.
Scientists refer to a so-called “contact angle”.
This angle is usually somewhere between zero and 120 degrees.
By comparison, water droplets on the lotus leaf have a contact angle of more than 150 degrees.
And the water droplet on the leafhopper’s wing has a contact angle of around 170 degrees.
Getting as close to 180 as gravity will let you
would give you an almost perfect sphere,
meaning the surface doesn’t even get wet when a bead of water touches it.
So chemists have been trying to figure out
how the lotus leaf and leafhopper’s wings do it.
And they’ve made a lot of progress in trying to get those super hydrophobic
for the contact angles of over 150 degrees.
There are sprays that can waterproof shoes which are commercially available in some places,
and ones that can prevent your white shirt from getting stained from red wine.
There’s even stencil street art in Seattle that only appears when it rains.
Or should we say, only doesn’t appear when it suns?
I don’t know.
To see some superhydrophobicity in action, we fired up the slow mo camera
and dumped water on superhydrophobic magic sand.
Here it is at 1000 frames per second.
But really, what I know you’ve all been waiting for
— the chemistry of how this works.
It all comes down to interactions we call surface chemistry
and the shape of the surface at a very small scale.
Most of the legwork is done by the surface
— essentially at the itsy bitsy nanoscale all the way up to the microscale,
the surface is NOT flat.
It’s actually very bumpy and rough.
These rough bumps are covered in a hydrophobic layer that has no time for water to join in
— sort of how water and oil never seem to get along.
So essentially the water is sitting atop a very oily,waxy bed of nails,
and it’s pushed upwards, away from the surface where it sits like a ball.
Because it’s on top of the surface, it can easily just roll away.
This is great for lots of products, like rain jackets that use water repelling Gore-tex,
which is made from Teflon, or as we like to call it polytetrafluoroethylene.
Car windshields and windows are coated with polysiloxanes to the same effect
–rain just rolls off instead of blurring your view.
One of the most innovative uses may be coming to San Francisco soon.
The city is testing a paint to deter public urination.
The hydrophobic paint would create a rough texture …
so that anyone who tries to go wee on a wall,
would, in fact, end up wetting themselves.
Thanks for watching us splash water around in the name of science.
For more, check out this great graphic from our friends at C&EN
and Compound Interest in the description below.
Thanks to Seattle Rainworks, Ultra-Ever Dry, and Dr. Mallory Hinks.
Do you have any experiments you want us to try?
Leave them in the comments,and Hey!
Thanks for watching.