[♪ INTRO]
No matter where you are, you likely encounter surfactants every day.
They’re a class of chemicals that show up practically everywhere,
from soap to sofas.
They’re a diverse group of molecules that are super useful
for their grease-busting and foam-making properties.
But despite what you may think when you hear the word “chemical,”
nature was using these sudsy molecules long before
humans adopted them for handwashing.
And the properties that make surfactants so great for us
also make them indispensable for animals that use them.
When horses run, they work up a lathery sweat.
This soapy effect comes from a surfactant in horse sweat called latherin.
This may seem like an incredibly odd way to sweat,
but the soapy suds are probably just a side effect.
The real utility of latherin most likely comes from its ability to spread
watery sweat across the animal’s oily, water-resistant coat.
And this ability has to do with latherin’s chemical structure.
One end of the molecule is hydrophilic —
it easily associates with water, the main ingredient in sweat.
The other end is hydrophobic —
it readily associates with the oily surface of the horse’s coat.
Latherin helps the sweat spread out into an even layer.
This way it evaporates more easily, to do what sweat is meant to do: cool the horse.
This two-sided property — one side hydrophilic, the other hydrophobic —
is a distinguishing feature of all surfactants.
And it’s why the surfactants in dishwashing and laundry detergents work so well
to break up dirt and grease.
The molecules’ hydrophobic ends are attracted to fat and dirt,
which they quickly surround.
The hydrophilic ends dissolve in water so that whatever the other end sticks to
can be rinsed away.
And the same properties may help latherin protect horses from bacteria.
Latherin has a lot of structural similarities to other molecules that make it harder
for bacteria to stick to each other, and to warm, wet surfaces.
So even though a horse’s sweaty skin seems like an ideal place for
microorganisms to grow, latherin could help to keep them from taking hold.
Army worm caterpillars use surfactants defensively too —
but in a really weird and creative way.
These little caterpillars eat a range of plants.
To process their food,
they make a cocktail of digestive juices, which includes surfactants.
One of the army worm’s main predators is fire ants.
When an ant attacks, the caterpillar basically throws up on it.
As you might expect, the ant immediately stops to groom itself.
The ants can’t tell us why, but it’s probably not because they’re grossed out.
This defense mechanism relies on another property of surfactants —
their ability to break the surface tension of water.
Normally, a droplet of water will bead up, because the water molecules are more
attracted to each other than the surrounding air, or to an ant’s exoskeleton.
Water molecules also repel the hydrophobic ends of surfactant molecules.
So they get pushed to the surface of the droplet.
But that disrupts the connections between water molecules at the surface.
So while pure water would normally bead up on the ant’s waxy exoskeleton
and roll off, adding a surfactant makes the drop spread out and stick.
The ant’s head ends up coated in a slick of nasty liquid.
And once they’ve been hit, the ants are unlikely to go back for another taste.
Surfactants’ ability to break surface tension makes them useful to humans
as a wetting agent.
Wetting agents help a liquid spread out on a solid surface,
and they come in handy for products like paint and cosmetics.
Of course, surfactants are also great bubble builders —
like you see with soaps and detergents.
Surfactants coat and stabilize the inner and outer surfaces of bubbles.
With some vigorous mixing, bubbles build up faster than they break,
and you get a foam — a whole mess of tiny gas bubbles trapped in a liquid or solid.
Some species of frogs have become foam experts.
The túngara frog builds floating foam nests for its eggs
on temporary water sources, like mud puddles.
The nests protect the frog eggs from all sorts of dangers, like parasites,
predators, harsh light, and extreme temperatures.
The surfactant-filled material for making the nest comes from the female frog.
During mating, the male frog uses its legs to stir it into a foam,
just like you’d use running water to froth up a bubble bath.
But, as you know if you’ve ever taken a bubble bath, foams are unstable.
The bubbles don’t last.
In manufactured foams, like the ones in mattresses and furniture,
you can add other chemicals to stabilize the bubbles.
And that’s exactly what the frogs do.
The female frog’s secretions also include foam stabilizers.
The baby frogs are usually ready to leave after about 3 days —
but the nests can remain stable for another week or so!
The frog surfactant, called RSN-2, is a robust bubble builder with the same soapy,
dual-sided properties as human-made surfactants.
But it’s unusually gentle.
This is crucial for the frogs, because the nest needs to be friendly to sperm,
eggs, embryos, and young tadpoles.
See, synthetic surfactants are really good at disrupting cell membranes:
that thin layer that surrounds all living cells.
That’s a useful property for soaps.
But not great for baby frogs.
So scientists are working to learn more about gentle surfactants like RSN-2.
That information could be useful for all kinds of applications,
like making edible foams, protecting wounds,
or building matrixes for tissue regeneration.
In other words, while we humans are proud of our clever chemicals,
we often find that nature did it first — and sometimes even better.
Thanks for watching this episode of SciShow,
which was made possible thanks to our amazing community of patrons.
You guys are the best, and we really rely on your support
to continue making free smart videos.
If you’re interested in joining, check out patreon.com/scishow.
[♪ OUTRO]