

A self-fueled liquid metal motor - freefrancisco
http://www.newscientist.com/article/dn27127-liquid-metal-brings-shapeshifting-robot-a-step-closer.html#.VQD16fmG-So

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anigbrowl
This was posted the other day, but surprisingly sank unnoticed. Here's a
repost of the comment I left then:

O.o The micro pumping and capillary action are extremely interesting, but
seeing how it deforms in response to an electrical current is just eye-
popping. Naturally I want to see what happens if you send AC signals rather
than static DC...at the least I would expect something similar to the behavior
of ferrofluids on a speaker cone, eg
[https://vimeo.com/65815077](https://vimeo.com/65815077) or even suspensions
of cornstarch:
[https://www.youtube.com/watch?v=dS9LNBQE2Jw](https://www.youtube.com/watch?v=dS9LNBQE2Jw)
which has a handy how-to at the end. The supplementary material is available
free even though the article is paywalled and is a great read.
[http://onlinelibrary.wiley.com/doi/10.1002/adma.201405438/su...](http://onlinelibrary.wiley.com/doi/10.1002/adma.201405438/su..).
The alloy is described here:
[https://gmwgroup.harvard.edu/pubs/pdf/1014.pdf](https://gmwgroup.harvard.edu/pubs/pdf/1014.pdf)
According to the supplementary, the aluminum flake 'fuel' is not consumed but
breaks up into tiny fragments and eventually diffuses to the surface, causing
the reaction to tail off. This seems like fairly fundamental research.

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anateus
The shape it makes when electricity passes through it reminds me more of
Lichtenberg figures:
[http://www.wikiwand.com/en/Lichtenberg_figure](http://www.wikiwand.com/en/Lichtenberg_figure)

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anigbrowl
Oh definitely, that's what I'd expect when you just pump electrons in it with
DC. But alternating current should lead to interference patterns of some sort.

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daniel-cussen
Music is Afrola by Bird Creek. To me, it made the video much more engaging.

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rounce
Indeed. Visions of Feynman doing a record with Fela Kuti are passing through
my mind right this instant.

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TrevorJ
Reminds me of those little soap-chip powered toy boats we made as kids.

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antsar
_When placed in a solution of sodium hydroxide, or even brine, and kept in
contact with a flake of aluminium for "fuel", it moves around for about an
hour._

So not quite self-powered.

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dang
We took "self-powered" out of the title.

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samatman
Chemist here: I think that's overly editorial. If there were an air-burning
engine made of aluminum, which consumed itself for motive force, we might
describe that as self-fueled. In general the reducing agent is considered fuel
and the oxidizer is assumed; a motor that oxidizes aluminum using hydroxide is
not that different from one that oxidizes it using oxygen.

Edit: The flake of aluminum fuel physically gloms onto the motor, and aluminum
will normally form an oxide that would prevent hydroxide (certainly brine)
from reducing it. It's not a 'mere' fuel that's physically driving the
droplet, there's a single reaction happening. My hunch is that's where the tin
comes in.

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dang
Thanks for the great comment! We put 'self-fueled' back in the title.

