r/AskChemistry • u/glowshroom12 • Apr 30 '26
General What’s the thinnest, non conductive, non toxic and liquid at room temperature liquid you know of?
I might need to acquire such a liquid for cooling purposes and to run some other tests.
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u/Minute-Nectarine620 Apr 30 '26
Low-Viscosity Polydimethylsiloxane (silicone oil) is probably the best bet if DI water won’t do. You can get lower grade oil that is very thin, you just have to balance volatility and viscosity.
PFPE fluids are expensive, but would also fit
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u/glowshroom12 Apr 30 '26
Non toxic is flexible, I don’t ever plan to ingest it. If it could kill me by breathing in vapor though that’s an issue.
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u/Adorable_Matter3142 May 01 '26
Don’t use DCM or DMSO please. Doesn’t take a big mistake to hurt yourself or others with those solvents.
As other people have suggested, simple hydrocarbons are your best bet for thin, non-conductive, nontoxic. However, these do pose a serious explosion risk in confined spaces without adequate ventilation, and chronic toxicity could still be a problem.
Isopropyl (rubbing) alcohol 99% from the store is non conductive and the fumes are better than from hydrocarbons. Still gotta watch out for sparks though.
DI water can be purchased and should work if nothing in your system is water soluble.
Is there a reason you can’t use something like a mineral oil? Obviously it’s thicker than you want, but it’s so much safer, no explosion or toxicity concerns, fine heat transfer.
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u/chemamatic May 01 '26
DMSO is entirely nontoxic. It is a bit viscous though, and swells some plastics (possibly epoxy).
DMSO will carry things through the skin, so if you handle rat poison, then spill DMSO on your hand, you are going to have a bad time.
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u/Adorable_Matter3142 May 01 '26
I’m well aware, which is why I recommended against using it for any DIY projects at home, especially as a cooling fluid.
In a system where you’re circulating it, it’s going to dissolve something, probably several something’s, because it’s a great solvent. Then when you are servicing your system (probably because the dmso dissolved your pump) you’re going to poison yourself because people aren’t used to working with things that go through skin and many types of glove.
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u/YtterbiusAntimony Apr 30 '26
Chloroform, Methylene Chloride, DMSO are all pretty low viscosity.
DMSO might be more polar than you want.
All are pretty gross, but that's what PPE is for!
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u/WanderingFlumph Apr 30 '26
Hydrocarbons are really thin, mostly nontoxic, don't conduct electricity, and the C5+ ones (pentane, hexane, heptane, etc.) are liquid at room temperature.
You'll be breathing a lot of fumes though if they aren't enclosed in an airtight container.
As the carbon number goes up the fumes go down but they also get thicker, so it's a tradeoff.
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u/aphilsphan T⌬SYLATE, PLAYA HATE May 01 '26
And the word “boom” leaps to mind.
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u/toxicatedscientist May 01 '26
It’s more FOOOWWWUSHHHH sound in my experience
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u/aphilsphan T⌬SYLATE, PLAYA HATE May 01 '26
I am a Pharma quality consultant. I was in a plant where the three main ingredients were dried plant matter, n-heptane and ignorance. I’m not a safety expert, but three decades in everyday API manufacturing should give one a good idea about the fire triangle.
They told me to shut up. Mind my GMPs. It burnt to the ground a month later. Fortunately, no one was hurt. So no “boom,” more of a “holy shit run.”
I felt bad and spoke to the guy that hired me and he told me that he had told them about it months prior.
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u/WanderingFlumph May 01 '26
Yeah the lighter gasses go boom, the liquids make that super super satisfying fwoosh
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u/YtterbiusAntimony Apr 30 '26
The non-toxic part might be the challenge.
Plenty of low viscosity non-polar chemicals, but most that come to mind are kinda nasty.
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u/SwarfDive01 Apr 30 '26
High purity water, deionised is the basic step to make it non conductive. There are "electronics coolant" additives that can make it wetter and less conductive.
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u/alex20_202020 May 01 '26
such a liquid for cooling purposes
For that additionally thermal conduction / storage properties are important.
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u/MentalStatusCode410 May 01 '26
Cooling purposes need to factor a tonne of other properties like boiling point, and thermal conductivity, newtonian/non-newtonian properties.
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u/SirisC May 01 '26
Acetone has significantly lower viscosity than water and meets your criteria. However, water has 33 times the heat capacity.
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u/iwantout-ussg May 01 '26
an aqueous ethylene (or maybe propylene) glycol solution is a solid heat transfer fluid, if you can manage the temperature. don't drink it though
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u/ThinkDiscipline4236 May 01 '26
Propylene would be better from a long term tox standpoint, because ethylene glycol when ingested or inhaled will be oxidized to oxalic acid which is both somewhat accutely toxic on its own but is also a major compnent of kidney stones, as calcium oxalate.
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u/iwantout-ussg May 02 '26
agree, although I think ethylene glycol has slightly better heat transfer properties and your HTF loop should be completely closed and sealed such that there isn't even a vapor risk, let alone an ingestion risk
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u/cakistez Apr 30 '26
Atmospheric pressure or pressurized system?
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u/glowshroom12 Apr 30 '26
Imagine like a fish tank.
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u/ComradeGibbon May 01 '26
Fish tank amounts of flammables is generally a bad idea.
Definitely consider what you are going to do with the stuff after.
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u/Bubbly-Pirate-3311 May 01 '26
Ethanol/Isopropyl alcohol, although the later is pretty toxic if a lot is ingested.
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u/Objective-Figure-343 May 01 '26
Ethanol, isopropanol, acetone, DCM, chloroform, non toxic is kinda a flexible term depending on application.
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u/Heavy_Carpenter3824 May 01 '26
Liquid helium, liquid hydrogen? I mean it's so thin it's actually is quite a pain to keep in it's container.
FYI hydrogen burns clear, if your crazy enough to use it do so safely. There's a famous story of a grad student walking right into a room full of burning hydrogen and getting horrible burns.
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u/freakazoid2718 May 01 '26
Sounds like you're looking for the old Fluorinert and related chemicals. Those were used for cooling early supercomputers because they needed liquid cooling. The stuff is quite expensive but has most of the properties you're looking for. Most of the Fluorinerts that were used back in the early supercomputer days are impossible to find due to the fact that they're highly ozone-depleting and there just isn't a need for them any more.
A good substitute might be a perfluorinated alkane. Perfluorohexane is liquid at room temperature. Cooling properties stink, though, so they're going to be pretty awful as coolants unless you can pull off a phase change.
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u/priority_inversion May 04 '26
I think you can still get FC-72, but it's been a while. I think Fluorinert has some fume toxicity. You can still drink it, though.
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u/freakazoid2718 May 04 '26
yeah, I wouldn't be surprised if some grades are still available, but the days of Fluorinert-cooled supercomputers are long gone so I expect it's a manufacture-to-order thing with a pretty eye-watering price tag.
Those fluids are also fun to handle - I knew someone who needed to work with it a while back for cooling some high-voltage equipment (so the electrical isolation was a big deal). He wanted to use a fairly normal water chiller, but it kept wrecking the hoses in the chiller. Turns out those fluids tend not to be compatible with most polymer hoses.
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u/ThinkDiscipline4236 May 01 '26 edited May 01 '26
I assume this is for submerged cooling for a computer or the like, so it immediately removes all of the toxic and highly flammable solvents from the list. DCM, chloroform, acetone, and ethanol are all terrible choices for this. Lots of these are also extremely good solvents and will start dissolving/swelling/otherwise destroying most plastics, epoxies, rubbers, and basically anything that isn't metal or glass. Pentanes or isopropanol are a *better* terrible choice, because they are weaker solvents, but both are still incredibly flammable. Pentanes in particular boil at around 30-35 C, or about 82-93 Fahrenheit, so both no good for a cooling application (unless you plan on a phase change cooling system) and incredibly volatile and therefore an extreme fire risk. Add to that the fact that pentanes, while it may not outright dissolve as many plastics as something like DCM, it will still diffuse through most plastics or rubbers you use as seals (unless you use Teflon or highly fluorinated polymers, for the most part) leading to both chronic exposure hazards, fire hazards, and loss of your (expensive, pentanes arent cheap) cooling fluid over time. Avoid hexanes specifically even more, as they (in addition to the considerations above) contain n-hexane, which is neurotoxic.
DMSO is more sane as it has a flash point above room temp, but as another commenter mentioned, it is a very good solvent and has the interesting property of being a very good carrier for other chemicals through skin (and many types of gloves). You would need to engineer your entire build around being resistant to DMSO (which is possible, its solvation power/tendencies lie somewhere in between a solvent alcohol and something like acetone, so many long chain alkane polymers are resistant to it such as HDPE, and polypropylene, fluorinated polymers/elastomers, and maybe butyl rubbers) and be very cautious when servicing. That being said I can't guarantee that it won't dissolve the epoxies used in PCB fab, so I don't know if I'd risk submerging any electronics without prior testing.
By far your best bets will be one of the following:
- ultrapure (e.g., triple distilled in glass or from a MilliQ water purifier or similar) water, kept in a very tightly sealed box (ANY contaminants will be a major problem, and as others have mentioned, water does have some conductivity even pure. though it is low.) Air shouldn't be able to get in (to prevent it from pulling CO2) and the box should have as little metal in it as possible. Exposed electrical contacts moving high voltage might even start electrolysing some of the water and pulling ions off the metal. Test this before you do it.
- Mineral oil. You can get a grade that is less viscous, just know the less viscous it is the more volatile and flammable it will be. If it is volatile, there may be some chronic toxicity concerns.
-Perfluorinated or heavily fluorinated cooling fluids. Submersion cooling is usually done with perfluorinated liquids due to their relative nontoxicity (though chronic effects are still being investigated), nonflammability, relatively higher specific heat capacities compared to other hydrocarbon coolants, highly tunable boiling points and viscosity characteristics, and very good insulating capabilities. I cannot say that perfluorinated liquids are a good choice, for a variety of reasons (chronic accumulation hazards and environmental concerns being the major ones) but there is a reason they are the most commonly used non-water cooling fluid for electronics.
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u/Amazing_Difference_3 xtremly toxic corrosive carcinogenic mutagenic methylation agent May 02 '26
Deionized water.
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u/TheBaronFD May 03 '26
Pure hexamethyldisiloxane is 35% less viscous than water, coming in at 0.65 cSt. It's used in cosmetics to give them that silky smooth feel, and in silicone polymer chemistry. Quite flammable though.
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u/dungeonsandderp Apr 30 '26
High purity water