Kind: captions
Language: en
now you've probably heard of the
Leidenfrost effect that's when a
volatile droplet likes water
levitates over a hot surface because
it's floating on a little cushion of its
own vapor here I'm gonna try to create
the inverse Leidenfrost effect where we
levitate a droplet on a bath of liquid
nitrogen its inverse because the droplet
is not actually creating the vapor it's
the bath beneath it's the liquid
nitrogen that's creating the vapor there
have been a couple of recent papers
about this phenomenon so I called up one
of the scientists to ask how can I do
this and how does it work
hello hi how are you I am doing very
well I was gonna ask you you think I
would be able to replicate this without
too much difficulty if you have liquid
nitrogen yes it's it's really simple
it's really basic what you need is
polystyrene box like 20 by 20
centimeters thick very dense whites and
then I had two beakers one like that
sighs and another one that is smaller in
which the experiments okay so when you
have a look at this setup I have a piece
of styrofoam that has a cylindrical
cutout in it into which I have poured
some liquid nitrogen and the purpose of
that is to get this outer space as cold
as possible and insulate it from the
rest of the air then I have this large
beaker that is full of liquid nitrogen
as you can see it is boiling and then I
have the innermost speaker which is not
boiling so I have still liquid nitrogen
in the middle that is not boiling and
that is what I want because that is
where we can actually conduct the
experiment and try to get the inverse
Leidenfrost effect to work okay I have a
hundred microliters of silicon oil and
I'm gonna attempt to drop it onto this
bath of liquid nitrogen whoa oh my god
look at that
what
there were a whole bunch of droplets and
they were all levitating on the surface
now that they are in there now the
liquid nitrogen is boiling so this is
not good
hey future Derrick here sorry my hair
looks stupid I'm gonna go get it cut
but that last experiment didn't go very
well because the liquid nitrogen in the
middle beaker was boiling and there was
nothing I could do about it
so I tested a few droplets on there but
you couldn't really see the effect
nicely because of that boiling bath so
I'm gonna try again today clean beakers
new liquid nitrogen let's give it a shot
there it is got a straw bit of silicon
oil and it is bouncing around back and
forth that is pretty cool what's amazing
about this effect is that it can
continue almost indefinitely it's been
observed to last for tens of minutes
unlike the Leidenfrost effect where the
droplet is used up making the vapor
cushion that supports it here the
supporting vapor comes from the bath so
it can continue indefinitely even after
the drop has frozen the heat required to
evaporate the bath comes not only from
the droplet but also from the warm
atmosphere around the experiment
although on my second attempt I was able
to prevent the small beaker of liquid
nitrogen from boiling my setup was a bit
unstable so the boiling in the outer
beaker shook the inner beaker
interfering with the droplets motion but
in NI ESA's professional setup you can
see how the drop always moves in
straight lines but why should the
droplet be moving at all and what keeps
it moving has been observed the
movements but nobody has tried to
explain it like yes so how did you
explain it there is something that
happens at the interface so you have a
floating drops with the thin vapor layer
above the bath and then what seems to
happen is that this vapor layer is not
uniformly thick but then at some point
there is a like a tiny instability like
a capillary waves that rose under it
well why is there a wave just for
example because I you'd never dip was it
to drop perfectly nicely and smoothly so
you create tiny waves that come back we
do the drop I think you can see that
here as I add a droplet to the bath
notice the waves generated in the middle
of the beaker these little waves lead to
an asymmetry underneath the droplet
where one side is higher than the other
more nitrogen gas escapes out this side
now you might think this would drive the
droplet in the opposite direction but it
doesn't the gas actually drags the
droplet along with it kind of like how
wind over your windshield pushes
raindrops along what is great here is
that this instability instantly
reappears each time the drop comes close
to wall so when you have a wall in the
bath you have a small liquid naturally
meniscus so the drop starts to climb in
and then the propelling force reverses
and then pushes it back and this creates
the nice star pattern so it's it's like
sulphur bail forever and repelled from
the walls which is which is very cool so
do you think this research has
applications and what sort of
applications might those be
if you imagine a number you of
like a mouse or something very very
young on Rio it's like 10 cells since
incredibly small so what they do is like
they put it into liquid that allows
cryopreservation and then freeze it and
and what is great about this is what
they do is they take the drop and put it
into liquid nitrogen and then it freezes
what and if the freezing is fast enough
you you don't grow ice crystals so you
preserve the embryo and and what is
great about this is like if you imagine
instead of just putting a noid drop
where what I did is like you put a
number you with the cryopreserve ins on
the liquid bath then you can you can
make it to canal like this and then you
can generate them like in a random way
and move them around because they are
self-propelled so they would go in the
direction that you want them to move so
you could imagine making something
wherever you could at the same time
freeze yourself or chemicals and then
move them along without generating any
contaminations because you're basically
not touching them that's an interesting
potential application of this hey this
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