I am a chemistry and physics double major doing some chemistry work in a nuclear physics lab. My mentor is a physicist, so his area of expertise is occasionally mismatched with what I need for my chemistry end of the project.

The scintillator fluid we use is commercially made, so I don't know all of the specific components, just that it is primarily diisopropylnapthalene (DIPN). I was trying to replace a LiCl emulsion (a standard scintillator cocktail component) with a lithium carboxylate.

I have tried dissolving my lithium salts into the scintillator, both the standard commercially-made one and a custom one that's the same composition but without the surfactants. Using only fractional molar concentrations (as low as 0.1-0.2 M) it turns milky. LiCl emulsions in our lab were stable between 1M to 10M, at least.

I know that water contamination can cause a milky emulsion to appear in oils. I think I used a strong enough desiccant to remove all the water, and I couldn't find -OH groups in IR spectra of my samples.

Could this be the O- parts of the carboxylates getting emulsified? Or something else? Why would my lithium carboxylates be milky but a LiCl emulsion not milky?

Any ideas would be great. I'm trying to understand the interactions going on here so I can either revise my methodology or choose new molecules to try. Thank you!

Edit: Given my UV-Vis data, the transmission was worse without the surfactants, which I think is because the surfactants made my carboxylates dissolve more easily. But I'm not sure if that has anything to do with the milky appearance.

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    $\begingroup$ Could you please mention which cocktail you use (e.g. Ultima Gold AB or similar)? Maybe it's not the solvent but one of the other components. $\endgroup$ – user7951 Mar 1 '18 at 18:11
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    $\begingroup$ @Loong It is indeed Ultima Gold AB (and a formulation that is the same but without surfactants)! $\endgroup$ – q-compute Mar 1 '18 at 18:38

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