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I am working on non-newtonian fluid project. I have experimented with cornstarch and water and achieved the consistency desired with 55% cornstarch and 45% water.

Now I want to create similar outcome using silica nanoparticles and polyethylene glycol (PEG 400). However, I am not able to reach a proper result. I used the following ratio: 60:40 (polyethylene and silica), but I got a paste-like material instead of a shear thickening fluid.

And ideas on how to find an accurate ratio for desired result? Is the problem regarding the ratio or the mixing steps? Do I need specific equipment for the process?

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    $\begingroup$ I remember reading an identical question with writing identical comment: By polyethylene, you must mean PEG. If you are sure it is right mixture, experiment with the ratio. Silika differs and may need variable ratio. $\endgroup$
    – Poutnik
    Jun 13 at 14:19

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Silica particles do show non-Newtonian fluid behavior but you need a much more concentrated suspension than simple cornstarch. Secondly, the solvent must wet the particles. The trick is to use a very small amount of solvent. Add a few drops of a solvent at a time, mix well (ideally sonicate) and then test it with a spatula. If it suddenly becomes hard upon fast motion of a spatula you have the right ratio.

If you wish to go a little deeper: Shear thickening is usually observed with dispersed suspensions. Look at a very dilute suspension of silica NPs and PEG under a microscope. If the particles are sticking together like grape-bunches, do not expect a shear thickening behavior in this solvent. Instead, such a suspension might be shear thinning like ketchup (which is difficult to test without a rheometer).

You can add this predictive behavior to your project if your school has an optical microscope. People might appreciate it.

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  • $\begingroup$ Thank you very much your answer is very helpful. Is there other ways to properly mix materials since I do not have access to sonication? $\endgroup$ Jun 14 at 11:46
  • $\begingroup$ Just mix with the help of a spatula. $\endgroup$
    – AChem
    Jun 14 at 12:33
  • $\begingroup$ I used a normal blender but did not help. I got a slime-like material instead of a non newtonian fluid. $\endgroup$ Jun 14 at 13:04
  • $\begingroup$ Blender cannot work with very concentrated suspensions. Try optical microscopy first. As I mentioned above not all suspensions are shear thickening. What is this school project about? $\endgroup$
    – AChem
    Jun 14 at 13:09

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