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Is there an additive that I can add to water that will increase the viscosity to a value between $5$ and $\pu{20 cP}$? Ideally, I would like the mixture to be newtonian and since I will be working with gallons of mixture, it would be nice if I didn't have to add too much of the stuff.

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  • $\begingroup$ 5 to 20 cP is a lot! I don't think simple addition of organic solvents can achieve that. What is the purpose? Polyols like glycerin are water miscible and they might be Netwonian. $\endgroup$ – M. Farooq Aug 12 '20 at 3:10
  • $\begingroup$ Do you have some own ideas about this? If you work with gallons of liquids, you must have some experience. (Btw. 1 cP = 1 mPas = pure water) $\endgroup$ – Karl Aug 12 '20 at 8:01
  • $\begingroup$ Without providing the purpose and acceptable additivce properties, the question is very unclear. $\endgroup$ – Poutnik Aug 12 '20 at 17:10
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You wasn't clear about your purpose to increase viscosity of water (water has viscosity of $\pu{1 mPa\cdot s}$ or $\pu{1 cP}$). However, whatever your reason, xanthan gum would be the materiel you are looking for. Kyoto Electronics has published a note on measurement of viscosity of xanthan gum solution. According to their results (average of 5 tests), 0.1% xanthan gum solution has shown viscosity of $\pu{19.1 cP}$. Five sample averages of 0.2% and 0.3% solutions have given viscosity readings of $\pu{57.54 cP}$ and $\pu{134.6 cP}$.

Accordingly, you can use range of percentages (0.01-0.1%)of xanthan gum to get water viscosity of $\pu{5-20 cP}$. The amount of material to add to water is minimal as you wanted. In addition, Casson plot (shear rate versus shear stress) of 0.1% xanthan gum solution is a straight line. Hence this solution is believed to be a Newtonian solution.

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    $\begingroup$ The key problem is that the OP wants Newtonian aqueous solutions i.e, viscosity should remain constant as a function of shear rate. Xanthan gum solutions may be non-Newtonian. $\endgroup$ – M. Farooq Aug 12 '20 at 5:49
  • $\begingroup$ @M. Farooq: Each solution (0.1%, 0.2%. and 0.3%) has a constant shear rate ($52.81, 22.87$, and $\pu{10.69 s-1}$). Do they Newtonian? $\endgroup$ – Mathew Mahindaratne Aug 12 '20 at 6:19
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    $\begingroup$ Dear Mathew, We need to a see a curve of viscosity vs. shear rate in order to decide whether the fluid is Newtonian or non-Newtonian. If it is a straight flat line, then the solution is Newtonian. Don't worry because the OP has still not bothered to clarify the purpose or the shear rate range. $\endgroup$ – M. Farooq Aug 12 '20 at 13:56
  • $\begingroup$ Thank you to everyone who responded. I've read about xantham gum, but haven't tried it. CMC is the additive I was thinking of, but I believe that CMC solutions are non-newtonian. $\endgroup$ – rdemyan Aug 15 '20 at 2:22

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