Kind: captions
Language: en
this is aerogel the world's lightest
that is least dense solid this piece has
a mass
of just 1.22 grams
that is only a few times the mass of the
same
volume of air which kind of makes sense
because it is
99.8 percent air in fact some air gels
are so light
that if you removed all the air from
them they would be
less dense than air i have long been
fascinated by aerogel so i actually flew
out to aerogel technologies in boston to
find out
why was aerogel invented how is it made
why is it such a good thermal insulator
and what is it used for
okay we are going to try an experiment
to demonstrate the insulating power of
aerogel so over here we have
uh two setups one with a glass petri
dish
and the other one with aerogel on top
both are made of silica
but with very different physical
structures we're gonna see how long it
takes to melt these chocolate bunnies
with a bunsen burner now to have a look
at this experiment we have a
fleur t1020 which can uh see
temperatures up to 2000 degrees celsius
it's getting pretty hot yeah you can see
that the glass is getting really hot
already and after just a minute it's
starting to smoke
oh uh okay it's definitely melting and
smoking oh yeah here we go
uh i would say that that's a phase
change we've got
a liquid chocolate situation we have
some smoking bunny
uh over here the bunny is actually sort
of melting over
and look there it's sort of tilting to
the side all right
i think we're going to call that a belt
what is that on cue on cue
[Laughter]
i would say that that's a material not
only did the bunny melt quickly
the petri dish cracked under the thermal
expansion
so now let's try the aerogel
so how was aerogel invented back in 1931
a guy named professor samuel kissler
had a bet with his colleague charles
learned now the bet
revolved around jellies like peanut
butter and jelly
jellies now the thing about jellies is
they are actually a combination
of liquids and solids i mean they're
mostly
liquid but it's embedded within this 3d
solid structure so if you think of a gel
like jello has a skeleton with
nano-sized pores that gives it its
rigidity
and then that's about one percent of the
gel so the bet was this
could you remove the liquid from the
jelly
without affecting the solid structure
i mean if you just evaporate the liquid
out well
then the solid structure shrinks because
as you remove
liquid molecules they pull on each other
and they pull on the solid structure
around them
basically crumpling it from the inside
now samuel kissler solved this problem
in two ways
first he realized you could replace one
liquid with
another inside the jelly just by washing
it thoroughly so you could swap out say
water for alcohol and then if you take
the jelly
and put it in a high pressure vessel
called an autoclave
by heating it to the high temperature
and high pressure point
called the critical point of the liquid
that liquid transformed into a
semi-liquid semi-gas called a
supercritical fluid
at this point there is no longer a
distinction between liquid and gas
those molecules are no longer pulling on
each other and so once you've
depressurized the vessel
that solid skeleton that one percent of
the mass of the gel
is left behind intact except for where
there was liquid in the pores before
is now gas and that solid skeleton that
nanoporous solid is what we call
aerogel kissler published his findings
in nature in 1931.
it is getting pretty hot as you can see
through the thermal camera
but coming up on three minutes there's
still no sign of melted chocolate
so we're gonna pull out a thermocouple
and just check the temperature
underneath
the bunny like underneath the air gel
and see what what the flame temperature
is
you can kind of see that the parts of
the bunny are getting hot
but it's not the bottom of the bunny
it's all the around the bunny
exactly that convective heat is moving
up and around the aerogel
so you can see the thing is getting red
hot and by four minutes the bunny's
looking a little soft
pretty good though considering how easy
it is to melt chocolate
can i put my finger here be careful
it's not that it's hot it's that it's
brittle right
but yeah totally cool to touch right it
is it is just warm to the touch
he made aerogels out of all sorts of
things he made them
out of eggs he made them out of rubber
out of nitrocellulose
and included in there was silica
actually right here on the table i have
some
examples of uh some silica gels
this is a wet silica gel it's kind of
rubbery
so i can just you know carve out a piece
it is
um 97
alcohol inside of its pores and then the
remaining three percent
solid is amorphous silica just uh can i
touch it
yeah absolutely it's kind of rubbery not
that strong
so was i cracking it there or was it
already kind of cracked no oh wow
very easy to break very crumbly the next
step is to replace the alcohol in the
gel with liquid carbon dioxide
we're about to see liquid co2 liquid co2
has the advantage of being non-flammable
plus it's got a low critical temperature
open up and
see it flooding in there yeah it's
flooding in there it goes it's just
another solvent
you can clearly see it's just so much
cooler
on top what temperature is it on the
bottom
we're at 600 right now 600 degrees
celsius
notice where the bunny is melting it's
melting right on that edge where the
heat's like the flame is kind of
crawling up and over so
again oh bunny down
well not a bad result not a bad result
at all
i'm interested in tasting some of this
chocolate here
gross
is it hot it's warm warm and delicious
like fondue
that was great once the liquid co2 has
filled all the pores of the gel
it's time to take it super critical it
was i would say kind of a spiritual
experience the first time that i saw a
supercritical fluid
i love how much you're into these
autoclaves i love air gels to make a
super critical fluid
we can heat this with a hair dryer
actually
as we approach the critical point the
surface of the liquid becomes kind of
blurry
weird huh that is like weird waves in
there
yeah i'll speed it up so you can watch
the surface disappear altogether
you're now looking at the supercritical
fluid of co2
in this state the co2 can be vented
without affecting the solid structure
and what you're left with
is aerogel if you look at aerogel
on a light background it's almost
impossible to see because it is
pretty transparent but if you look at it
on a dark background then you can see
that it has
a slight bluish color and it's bluish
for the same reason
that the sky is blue because all those
tiny little nanoscale structures
they scatter the light according to
rayleigh scattering
and the intensity of light scattered is
proportional to one over wavelength to
the power of 4 which means it scatters
shorter wavelengths like blue
much more than it scatters yellow or red
and for that reason aerogel looks opaque
in the ultraviolet
and transparent in the infrared
now what do you think this would look
like if i held it up to the blue sky
what do you think we would see would it
look ultra blue
no it looks yellow and that's because
the air gel is actually scattering out
that blue light
and so what passes through and makes it
to our eyes is the longer wavelengths
like the yellows and oranges
it's basically the same effect as
looking at a sunset
when you see the yellows and oranges of
a sunset it's because the blue light has
already been scattered out by the
atmosphere
the light had to pass through before it
reached your eyes
so effectively looking at aerogel
against blue sky is like
looking at a portable sunset the
nanoscale pores of the aerogel are also
what makes it such a good thermal
insulator
that's awesome does that look hot it's
definitely hot you might
think that because aerogel
is largely comprised of air like 99
air that has the same thermal properties
as air
but that is not correct it's actually a
better insulator than air is
that's because the width of the pores is
smaller than the distance
air molecules travel on average before
colliding with something
their so-called mean free path hence
it's really difficult for the hot
fast-moving air molecules below the
aerogel
to diffuse through it and transfer heat
to the top of the aerogel
this is called the knutson effect it is
so weird because
you know you don't expect something
that's transparent to
block the heat that well but this
really does and that's why nasa used
aerogel insulation on the sojourner
rover spirit and opportunity
the curiosity rover and they plan to use
it on future missions to mars
why does it need insulation the
electronics because
uh they don't want the electronics to
get cold during the cold
nights on mars nasa has also put aerogel
to more exotic uses
notably to catch dust from a comet as
part of the stardust mission
so the particles were traveling about
six kilometers per second relative to
the aerogel
so when they hit the aerogel because the
aerogel is a very low density material
very very porous material the particles
actually enter the aerogel and as they
travel through the aerogel they
basically break apart the network that
makes up the aerogel and they lose
energy in the process and eventually
come to a stop
this is good for capturing particles
because if a particle like that were to
hit a solid
surface then it just stops you know
immediately and just vapor and vaporizes
so should we expect to see aerogel in
our everyday lives anytime soon
one of my running jokes is when they
build skyscrapers in antarctica they'll
they'll use aerogel as thermal
insulation
why do you say that well because then
they'll really care about
how just how thermal efficient is
because it'd be so cold there
right so instead of having you know 10
feet of
fiberglass insulation you could have six
inches or something of
of aero gel scientists are currently
working on reducing costs and increasing
durability
and that's that's true they they do have
some elastic okay yeah so there we go
so it is not hard to break they've
already made a lot of progress
for example original silica aerogel is
hydrophilic
there we go now this is a hydrophilic
aerogel
so once we've done this is that piece of
air gel ruined now
pretty much but there are ways to make
it waterproof
so if you want to see that and all the
other next generation error gels then
subscribe to the channel
and this may be the start of an aerogel
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trilogy
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you