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Non Newtonian Fluid


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 Nano particles 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?
Thank you. 

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New Contributor

Re: Non Newtonian Fluid


I'm having the same problem with a silica (Aerosil 200) and PEG400 mixture. The mixture didn't become dilatant like Oobleck. How can I obtain a dilatant fluid like Oobleck using SiO2 and PEG400? It should behave like a solid under pressure. Thank you.

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Re: Non Newtonian Fluid

Creating a non-Newtonian fluid, particularly a shear-thickening fluid (STF), using silica nanoparticles and polyethylene glycol (PEG 400) involves careful consideration of both the ratio of components and the mixing process. Here are some detailed steps and considerations to help you achieve the desired shear-thickening properties:

Understanding the Components and Their Roles

  1. Silica Nanoparticles:

    • These act as the dispersed phase in the STF, providing the solid component that interacts under shear to cause thickening.
    • The particle size, shape, and surface characteristics significantly influence the behavior of the STF.
  2. Polyethylene Glycol (PEG 400):

    • This acts as the dispersing medium (continuous phase) and affects the fluidity and interaction between silica particles.

Key Factors to Consider

  1. Ratio of Components:

    • The ratio you use (60:40 PEG to silica) might be too high in PEG, preventing the formation of a proper network needed for shear thickening.
    • Adjusting this ratio is crucial. Typically, higher concentrations of nanoparticles (up to a certain limit) favor shear thickening behavior. You might need to try higher silica content.
  2. Dispersion Quality:

    • Proper dispersion of silica nanoparticles in PEG is critical. Clumping or agglomeration of particles can prevent the formation of a uniform STF.
    • Use ultrasonic bath or probe sonication for better dispersion.
  3. Particle Size and Distribution:

    • Ensure the silica nanoparticles are of a consistent size and well-dispersed. Variations in particle size can affect the rheological properties.
    • Surface treatment of nanoparticles can improve dispersion and interaction with PEG.
  4. Mixing Process:

    • The mixing process must ensure complete and uniform dispersion. Use high-shear mixing, magnetic stirring, or sonication to achieve this.

Step-by-Step Procedure to Find the Accurate Ratio and Mixing Process

  1. Preparation of Silica Nanoparticles:

    • Ensure your silica nanoparticles are dry and free-flowing.
    • If necessary, dry them in an oven to remove any moisture that might affect the mixing process.
  2. Initial Mixing:

    • Begin by slowly adding PEG 400 to a measured amount of silica nanoparticles while stirring continuously to prevent clumping.
    • Use a magnetic stirrer or mechanical mixer for initial blending.
  3. Ultrasonication:

    • Subject the mixture to ultrasonication. This step helps break down any agglomerates and ensures uniform dispersion of nanoparticles.
    • Perform sonication in intervals to prevent heating, which could alter the properties of PEG.
  4. Adjusting Ratios:

    • Start with a higher concentration of silica nanoparticles, such as 65:35 (PEG
      ) or 70:30, and observe the changes in viscosity and shear-thickening behavior.
    • Gradually decrease the PEG content until the desired shear-thickening properties are observed.
  5. Testing and Evaluation:

    • Test the mixture under shear (using a rheometer, if available) to observe the thickening behavior.
    • Adjust the ratio and mixing process based on the results. Aim for a balance where the mixture is fluid under low shear and thickens significantly under high shear.

Specific Equipment for the Process

  • Rheometer: To measure the shear-thickening properties accurately and quantify the viscosity changes under different shear rates.
  • Ultrasonicator: For ensuring a uniform dispersion of silica nanoparticles in PEG.
  • High-Shear Mixer: To facilitate proper blending of the components.
  • Magnetic Stirrer: For continuous and uniform stirring during initial mixing.

Troubleshooting Tips

  • Consistency: If the mixture remains paste-like, the silica content might be too high. Gradually adjust the ratio and test until you find the optimal balance.
  • Temperature Control: Maintain a consistent temperature during mixing and testing as temperature variations can affect viscosity.
  • Incremental Adjustments: Make small incremental adjustments to the ratios and thoroughly test after each change. Official Libgen Portal

By carefully adjusting the ratios and optimizing the mixing process, you should be able to achieve a shear-thickening fluid with silica nanoparticles and PEG 400 that meets your desired specifications.

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