Tran Luat

Use polyethylene oxide. The higher the viscosity of the suspension, the more stable the suspension will be.

Yuri Mirgorod you mean add PEO to increase the viscosity avoid agglomerating, so could you recommned another solution.

There is so much unknown here:

• The size (and dispersion state) of the silica particles which will contribute to any (potential) settling
• The porosity of the particles which will alter the apparent density and thus any (potential) settling
• The surface make-up of the silica - there are many types from hydrophilic to hydrophobic. This affects the wetting of the particles - you can't work with hydrophobic systems in water without the use of an appropriate surfactant
• What you mean by 'stability' - absence of settling? No aggregation/agglomeration?

40g silica in 100g water is a 400/14 wt% (~ 29 wt%) system and this is particularly high.

As one example, consider this reductio ad absurdum argument. 40g of silica with an assumed density of 2.5 g/cm3 occupies a space of 40/2.5 or 16 cm3. Thus, a piece/block of quartz 2 X 2 X 4 cm would sit nicely on the bottom of a beaker and 100 mL of water could be added to it. The system would be completely stable. Is this what you mean?

If you just need "stable dispersion of SiO2 in H2O", just buy Ludox (R). Otherwise, more details are needed (see Alans answer)

To create a stable suspension of 40 grams of silica in 100 grams of water, there are several methods you can use. Silica particles are often hydrophilic and can aggregate, so stabilizing the suspension involves preventing this aggregation. Here’s what you can do:

1. Use a Dispersing Agent (Surfactant or Stabilizer)

• Polymer Dispersants: Adding a small amount of dispersing agents like polyvinyl alcohol (PVA), polyacrylic acid (PAA), or another polymer can help to stabilize the suspension by preventing the silica particles from agglomerating.
• Surfactants: Non-ionic surfactants (like Triton X-100 or Tween 80) can help reduce surface tension and improve dispersion.

2. Sonication

• Ultrasonic Treatment: Use an ultrasonic bath or probe sonicator to break up any agglomerates and ensure the silica particles are finely dispersed. Sonication can apply energy that helps to disperse the silica particles more evenly in water, improving the overall suspension quality.

3. pH Adjustment

• Silica particles can have a surface charge that influences their behavior in water. Adjusting the pH of the solution can help to enhance the electrostatic repulsion between particles. Silica tends to be more stable in slightly alkaline conditions (pH 8-10), where the surface charge of silica becomes more negative, which can help to keep the particles apart.
• To do this, you can use a small amount of sodium hydroxide (NaOH) or potassium hydroxide (KOH) to raise the pH, but be cautious not to go beyond the point where silica dissolves in the solution.

4. High Shear Mixing

• Use a high shear mixer to disperse the silica more effectively. High shear mixing generates strong forces that help to break up aggregates and keep the particles evenly distributed in the liquid.

5. Viscosity Control

• Adding a small amount of thickener or viscosity enhancer like xanthan gum, guar gum, or even a polymeric stabilizer can help the silica remain suspended for a longer time. It increases the viscosity of the solution, making it more resistant to sedimentation.

6. Temperature Control

• Silica particles tend to be more stable in cooler environments. Consider performing the dispersion process at a lower temperature to help reduce particle aggregation. However, excessive cooling can lead to clumping, so moderate temperature control is advised.