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I'm trying to create an experiment where two immiscible liquids are mixed and are then separated by density. Most of the container is occupied by the lighter liquid, and the small amount of heavier liquid sinks.

Then, a third liquid, immiscible with the other two is added, in amounts intermediate between the two. This liquid is lighter than both of the other liquids and floats.

However, this 3rd light liquid can wet the dense liquid, and after mixing it carries it upwards to the top of the container, basically creating a flotation process.

Here's a rough sketch of what I want to achieve:

enter image description here

I don't care if after the last step the dense liquid then sinks again through the light liquid. If the dense liquid is elevated, even temporarily, that's good enough.

This is slightly similar to industrial flotation processes that separate ore minerals from a slurry of crushed rock. Air bubbles "wet" surfaces of heavy minerals such as copper sulfides and lead sulfides, and float them to the top of a container. In my case I'm talking about three liquids and not a liquid, solid, and a gas.

The reason I'm asking is that I created something similar at high pressure and temperature (~1 GPa, 1000 C) in a sealed pressure vessel and I'm looking for a good way of demonstrating this phenomenon in a more accessible way.

Is there such a thing? I have access to common (and some uncommon) chemical reagents. The liquids have to be transparent, obviously, to see the entire thing. Preferably coloured, or possible to colour them.

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  • $\begingroup$ That's a tough one. When two liquids "wet" each other, they usually also dissolve each other, so your 1st and 3rd would end up being just one liquid. You may be able to adjust its density so that it would float as a sphere in the 2nd liquid, but that's another story. $\endgroup$
    – Ivan Neretin
    Apr 1, 2016 at 8:24
  • $\begingroup$ @IvanNeretin it also could be that instead of adjusting density, you could adjust the phase proportions.. $\endgroup$
    – Gimelist
    Apr 1, 2016 at 22:02
  • $\begingroup$ Do you mean that a third liquid causes a phase inversion? $\endgroup$
    – Beerhunter
    Apr 1, 2016 at 22:10
  • $\begingroup$ @Beerhunter what do you mean by phase inversion? $\endgroup$
    – Gimelist
    Apr 1, 2016 at 22:10
  • $\begingroup$ I read an older version of the post and missed that the 3rd liquid is also immiscible. I have experienced dissolving a (solid) product which has caused the normally less dense phase to actually be the lower layer in a water-solvent mixture. This is what I'm referring to as a phase inversion. Your query is different due to the most dense phase being dispersed in your least dense phase. $\endgroup$
    – Beerhunter
    Apr 1, 2016 at 22:22

1 Answer 1

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https://www.youtube.com/watch?v=GRPufqPgTeI

I played around a bit with this in the lab and this is what I came up with. Basically, I made a three phase system with hexanes on top, water with fluorescein and green food colouring in the middle, and a perfluoroalkylether HT-110 on the bottom. Just finding three mutually immiscible liquids was pretty challenging and unfortunately, like most highly fluorinated liquids, HT-110 is almost twice as dense as the other two liquids, but if you look at the video carefully, you can see that some bubbles of HT-110 are getting trapped in the hexanes as its surface energy isn't quite as high in hexanes as it is in water. When I tilt the vial on its side, you can see these bubbles snapping back across in the interface.

It's not perfect, uses a goofy solvent, and I probably could have played with the liquid ratios/container shape to trap more HT-110 at the top, but it seems that something at least similar to what you're after can be made fairly simply.

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  • $\begingroup$ So let's see if I understand what's happening. You first have the three liquids in layers. When you shake it, "as its surface energy isn't quite as high in hexanes as it is in water" - you mean that it "wets" it preferentially? Anyway, the bubbles of HT 110 are trapped in the hexane, and they can't sink down through the water because they "stick" to the hexane. When you tilt it, they sink again to the HT 110 again. $\endgroup$
    – Gimelist
    Apr 5, 2016 at 3:34
  • $\begingroup$ Would it be possible to add colouring to either the hexane or the HT 110? Does it matter if it's HT 110 or any other fluorinated liquid? Does it matter which hexane? $\endgroup$
    – Gimelist
    Apr 5, 2016 at 3:35
  • $\begingroup$ I actually tried adding a porphyrin dye to the hexane, but it wasn't soluble. There are many dyes that would be soluble in the hexane and not the water, I just don't have any handy. The HT-110 isn't likely to dissolve many normal dyes. I don't think it has to be HT-110. Most highly fluorinated liquids have these kind of omniphobic characteristics. (Sigma sells FC-40 and the like) It was a mixture of different hexane isomers—your normal lab solvent grade. $\endgroup$
    – Michael DM Dryden
    Apr 5, 2016 at 4:33
  • $\begingroup$ I don't know if I would call the interaction wetting exactly, as the term usually refers to liquid-solid interactions, but what I mean is that it's more energetically costly to have a HT-110/water interface than a HT-110/hexane interface, which means, for a certain size of droplet, gravity isn't enough to pull the droplet through the water. $\endgroup$
    – Michael DM Dryden
    Apr 5, 2016 at 4:36
  • $\begingroup$ That's why I was referring to "wetting" in quotes :) Thank you! This is exactly what I was looking for. $\endgroup$
    – Gimelist
    Apr 5, 2016 at 4:46

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