Naked Science Forum
Non Life Sciences => Chemistry => Topic started by: Kryptid on 19/06/2018 16:46:51
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Gels are mostly liquid but are held together by a three-dimensional network of cross-linked polymers that give them their shape and stability. Most often, the liquid in question is water. However, would it be possible to create a gel where the liquid content was a liquid metal instead, such as mercury or galinstan? Given that organic polymers do not seem a good candidate for use in liquid metals, could a substitute be used? What about very fine fibers of another metal? What about silicon or polystannanes (tin polymers)?
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After doing a bit more research, I think I have a little more of a handle on the idea. In normal gelatin, a carbon polymer backbone is able to hydrogen bond with the water it is suspended in due to hydroxyl and amino groups on the chain. A way to mimic this in a metal solvent may be to use an ionomer backbone. In an ionomer, there is a carbon polymer chain that has negatively-charged substituents such as carbonate or nitrate groups that are attracted to metal ions around them (such as sodium).
If we were to use a liquid metal like galinstan, an ionomer with gallium, tin or indium cations would be preferred. I have read that metal salts are often soluble, at least slightly, in molten metal of the same type (i.e. sodium chloride in molten sodium). I imagine this is because neutral sodium atoms easily pass their electrons on to sodium ions and back again (since electrons wouldn't prefer whether to be around one sodium atom or another). Something similar may work to give a tin, gallium or indium ionomer some solubility in galinstan. I'm guessing it would probably need to be heated up to more fully dissolve the ionomer and then cooled off to bring it out of solution and form the gel. It's a shame I'm not sure where to get the needed ionomer to perform the experiment myself.
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Metals are held together by the sea of electrons they share.
They aren't so likely to "wet" insulators that don't share this sea of electrons.
So I suggest that a framework of sintered metal with lots of pore space could absorb a liquid metal, forming a metallic gel. The test would be to see if the liquid metal "wets" the solid metal, and wicks up into the pores.
You may need to watch that the electron energy levels match between liquid and solid framework. If the energy levels don't match, you could end up with a Schottky barrier which blocks electron sharing. I'm not sure what this would do to the meniscus.
See: https://en.wikipedia.org/wiki/Schottky_barrier
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Very interesting question! I will have to think about it some...
Initial thoughts (more questions):
Gels are often created by first creating a stable solution, and then cooling it to precipitate out a minor impurity, which interacts with itself to create a network within the liquid. Thus you would need a liquid metal (like mercury, galinstan, or NaK--or you can work at elevated temperatures with relatively low melting metals like gallium, cesium, potassium, sodium, tin, zinc, bismuth etc.) and another compound or metal that is only slightly soluble in the liquid at one temperature, and is more soluble at a higher temperature...
Do you want the whole gel to be metallic, or just have a metallic liquid (or a non-metallic liquid with a metallic gelator?)
EDIT: Some additional thoughts: you will also want to make sure that the densities of the two materials is not so different that the minor components just precipitates to the bottom or forms a scum at the top. This might rule out mercury as the liquid component (13.65 g/cm3) unless you can find an adequately dense gelator (even lead at 11.5 g/cm3 is not nearly dense enough).
You will also want to avoid chemically incompatible materials (this is most likely to be problematic with highly reactive metals like NaK)
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Ideally, I wanted the entire thing to be made of different kinds of metal, but I wasn't sure if that was possible.
What you say about density is a good point, as even galinstan has a density of 6.44 g/cc, which is probably much higher than any organic polymers or ionomers that I was considering using. A density that high will probably require using another metal network like what evan_au suggested. You could probably create a solid alloy of equal density to galinstan by carefully controlling the proportions of each element in it, but would need to be careful not to use metals that dissolve in galinstan.
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I suspect that this high tech approach may be as good as it gets. A paste, rather than a a gel.
https://en.wikipedia.org/wiki/Wiped_joint
(High tech from 2000 years ago, that is)
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This may be of interest.
https://www.sciencedirect.com/science/article/pii/S0010854513000131
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This may be of interest.
https://www.sciencedirect.com/science/article/pii/S0010854513000131
Interesting find, but I don't think it is directly relevant--the gelators discussed in the article contain metal atoms, but they are not metallic. Rather, they are organometallic or metal organic complexes (these are the sorts of compounds I study, though not for making gels).