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I have tried searching everywhere for a stable, non-volatile, bio-safe, low viscosity (< .8cST) fluid. Everything I have come across that is low viscosity is inflammable - acetone, ether, silicone oil, fuel, etc.

I have found some confusing things in my research. Acetone has a viscosity 3x less than water but weighs 2.5 times more. I would like to know how water weighs less but flows slower. Google says viscosity is from low intermolecular forces, but I do not know how to quantify those forces or how to find chemicals that match.

I am trying to make a science project that shows the principle of siphoning, but I want a lower viscosity liquid to show how viscosity effects flow rate. I am working with glass right now and PVC tubes, but I can change my materials based on whatever low viscosity liquid you can find.

Also if anyone knows anything about siphoning, viscosity or material chemistry please let me know if there is a database I can search or if you know chemical that is less viscous than water and meets my specifications.

Is there something I can add to water to lower the viscosity aside from heating? I do not want to have boiling water in my hands. I hear there are surfactants that lower the viscosity of water, but google says surfactants increase viscosity.

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    $\begingroup$ Why do you say acetone "weighs 2.5 times more" than water? Its density is less than 80% that of water. Could you not do your demonstration comparing water and something more viscous than water? $\endgroup$
    – jeffB
    May 15, 2019 at 2:53
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    $\begingroup$ Low viscosity and non-volatility are rather mutually exclusive requirements, as the former requires low intermolecular interactions, while the latter the direct opposite. $\endgroup$
    – Poutnik
    May 15, 2019 at 3:38
  • $\begingroup$ Welcome to the site! This sounds like an interesting and fun problem! I look forward to seeing what kind of answers others come up with. I did notice you seem to have several questions nested in this question. Would you be willing to post each question separately? It would help break down your problem by its parts and help you get the answers to all your questions. $\endgroup$
    – Melanie Shebel
    May 15, 2019 at 5:15
  • $\begingroup$ The Mw of water is smaller than that of acetone, yes. Water is protic, it hydrogen bonds extensively (self-associates) which explains the viscosity and high b.p. despite low MW. Acetone is polar aprotic, no h-bonds. $\endgroup$
    – Buck Thorn ♦
    May 15, 2019 at 7:45
  • $\begingroup$ Have you checked out “viscosity reducing additives”? Long ago, I used to add polyethylene oxide (“PEO”) to water to make “liquid banana peel” for fun in the freshman dorm. $\endgroup$
    – Ed V
    May 10, 2021 at 15:46

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There is one class of available liquids (some readily available from chemical suppliers eg perfluorohexane) that might fit the requirement: perfluorocarbons.

They have similar boiling points to hydrocarbons with the same number of carbons (so room temperature liquids with > 5 or 6 carbons). And they typically have low viscosity when compared to their hydrocarbon equivalents which, in turn, then to be less viscous than water.

This class of compounds were once investigated as blood-substitutes as the solubility of oxygen in them is very high. And some are used in other medical procedures today. Which suggest they are not acutely toxic.

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I guess you could go with Peppermint essential oil. Its density is 0.898 g/mL at 25 °C. It obviously is volatile to some extent if left uncovered however its viscosity is considerably lower than water. Hope this helps you out!

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