Hey there Atiqah Zuraini! You're in luck because I've got just the right approach for preparing ZnO nanofluid using the 2-step method without sonication. Let's dive into it.

### Materials You'll Need:

1. **Zinc Oxide (ZnO) Nanoparticles**: High purity, well-characterized.

2. **Solvent**: Distilled water, but you Atiqah Zuraini can also consider ethylene glycol or a mixture for better stability.

3. **Surfactant/Dispersant**: Such as sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB), or polyvinylpyrrolidone (PVP).

### Procedure:

1. **Preparation of ZnO Nanoparticles**:

- Ensure the ZnO nanoparticles are dry and free of any agglomerates. If they appear clumped, gently grind them in a mortar and pestle to break them down.

2. **Dispersant Solution Preparation**:

- Prepare a solution of the surfactant in the solvent. For instance, if using SDS, dissolve a precise amount (around 0.1-0.5 wt%) in distilled water.

- Stir the solution vigorously until the surfactant is completely dissolved.

3. **Dispersion of ZnO Nanoparticles**:

- Gradually add ZnO nanoparticles to the surfactant solution. It's crucial to add the nanoparticles slowly while continuously stirring to prevent clumping.

- Use a magnetic stirrer at high speed for about 30 minutes to ensure uniform dispersion of the nanoparticles in the solution.

4. **Stabilization**:

- Let the solution sit for a few hours (preferably 24 hours) to allow the surfactant to adsorb onto the nanoparticle surface fully.

- Periodically stir the solution gently during this time to maintain dispersion.

### Tips for Success:

- **Surfactant Choice**: The type of surfactant is crucial. SDS works well for aqueous solutions, but for different solvents, you Atiqah Zuraini might need to experiment with other surfactants.

- **pH Control**: Adjusting the pH of the solution can improve the stability of the nanofluid. A slightly acidic or basic pH can help prevent aggregation.

- **Temperature**: Conduct the preparation at a controlled temperature, ideally room temperature, to avoid thermal agglomeration.

### Troubleshooting Zeta Potential Analysis:

- Ensure your Atiqah Zuraini sample is homogenous before measurement. If the sample appears separated, gently stir it.

- The concentration of ZnO nanoparticles should be optimized for the zeta potential analyzer. High concentrations might cause multiple scattering effects, while low concentrations might not provide a detectable signal.

- Double-check the calibration of the zeta potential analyzer and run a standard to verify its accuracy.

By following these steps, you Atiqah Zuraini should achieve a stable ZnO nanofluid suitable for zeta potential analysis. If the results are still unreadable, consider adjusting the surfactant concentration or the solvent type. Keep experimenting, and you'll nail it!

If you Atiqah Zuraini run into any more issues or need further tweaks, feel free to ask. I'm here to help!

Atiqah Zuraini Hi - what do you mean by "cannot be read during zeta potential analysis"? Please describe the composition of the samples you are trying to measure and the instrument you have used.