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This may just be a straight-up chemistry question, but it's got a distinctly world-building motivation, so...

Hal Clement, in his novel Iceworld, posits the existence of hot-world aliens living at temperatures above 500C with copper chloride as a biosolvent. This is very relevant to descriptions of their homeworld and interactions with humans, but the detailed biochemistry... not so much.

Nevertheless, I want to know more! Is this actually somewhat plausible, or 100% handwaving?

So, at the most basic level, cellular compartmentalization of terrestrial life depends on the existence of a difference between lipophilic and hydrophilic chemical phases, which allows micelles and bilayer membranes to self-assemble. I have tried to find out if a similar kind of chemical phase separation is possible in molten salts (like copper chloride) or other ionic liquids, but that turns out to be incredibly difficult to google, because the results are all about phase separation induced by dissolving salts in water (i.e., "salting out").

So... is chemical phase separation, such as might be useful for producing "oil" drops, micelles, or membranes, possible in molten salts? If so, what kinds of molecules might form micelles or vesicles in a given molten salt ionic solvent system?

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  • $\begingroup$ It looks like you're asking about how realistic something is in an existing fictional world, as opposed to asking about building a fictional world. Discussions about existing works are off topic on this site. $\endgroup$
    – sphennings
    Feb 7, 2022 at 19:55
  • $\begingroup$ Hmmm. The vast majority of organic compounds tend to do less than well at temperatures over 500 °C. (Certainly there would not be anything like our common fatty acids, for example, so that "lipophilic" must mean something else.) So that the first thing to do is to try to find a set of chemical structures which could be used to take the place of our ordinary carbon-carbon organic chemistry at such high temperatures, and then try to find their properties. $\endgroup$
    – AlexP
    Feb 7, 2022 at 20:07
  • $\begingroup$ @sphennings Iceworld is only the inspiration; the specific chemistry of that world is not at issue, but rather the much broader subject of ionic fluid / molten salt chemistry in general, with application to building other worlds. If copper chloride turns out to be a terrible choice, making Iceworld unrealistic, that does not invalidate the possibility of creating a different world based on a different salt. $\endgroup$ Feb 7, 2022 at 20:14
  • $\begingroup$ @AlexP There are ionic compounds with much lower melting points than that, so fortunately the organic stability issue can be sidestepped. It looks like molten sodium and potassium hydroxides support acid / base chemistry, so that's encouraging.... $\endgroup$ Feb 7, 2022 at 20:16
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    $\begingroup$ This is a worldbuilding question rather than a chemistry question, because the motivation to describe a fictional life form unifies what we hope will be a wide range of potentially interesting but different proposed cell membrane chemistries that have no direct chemical relationship with each other. $\endgroup$ Feb 7, 2022 at 21:28

1 Answer 1

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Metal.

The Solubility of Some Metals in their Molten Halides

The apparent solution of a number of metals in their molten salts has been known for nearly two centuries. Interpretation of this behavior as being due to colloid formation led Lorenz2 to introduce the term “pyrosole” to describe the phenomena. The formation of intensely colored melts, the occurrence of visible metal particles in the quenched salt, and the repression of the extent of metal solution by the addition of foreign salts were all considered evidence for the formation of colloidal metal in the molten salts.

"Colloidal metal" is pretty close to what you were looking for (even if it turns out it is not exactly a colloid with the metal). The metal dissolves in the salt to an extent, but blobs of molten metal persist. Other metals besides the one comprising the salt can also dissolve in the salt (for example, cadmium dissolving into molten copper chloride) and these other metals form their own chlorides, their own metallic droplets, and droplets of mixed metal chemistry.

Science is familiar with metal chemistry in geology and especially the formation of alloys for various industrial purposes. One could imagine a world where metal chemistry and electrochemistry was the stuff of life.

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