Dispersing Silica Dimethyl Silylate in Lip Gloss

Dispersing Silica Dimethyl Silylate in Lip Gloss

Hello, I understand the issue you're facing with dispersing Silica Dimethyl Silylate in your oil-based lip gloss formula. Silica Dimethyl Silylate is effective for increasing viscosity and suspending pigments in oil formulas, but achieving a smooth, lump-free dispersion without air bubbles requires the correct technique.

Silica Dimethyl Silylate is a derivative of Fumed Silica that has been surface-treated to be more compatible with oils. However, it still tends to aggregate due to its particle structure. Dispersing this group of materials in oil requires sufficient shear force to break down these aggregates and achieve uniform dispersion.

Regarding your question about using a propeller or a sawtooth/dispersion blade with your overhead stirrer:

• Propeller: Suitable for general mixing that promotes liquid flow but provides relatively low shear. This may not be sufficient for smoothly dispersing Silica Dimethyl Silylate, especially at 1% concentration, where good dispersion is needed to prevent pigment settling.
• Sawtooth/Dispersion blade: Designed to generate high shear force, making it ideal for dispersing powders in liquids, such as pigments or thickeners that require shear for dispersion. Using a sawtooth blade will help break down the lumps of Silica Dimethyl Silylate more effectively than a propeller, resulting in a finer dispersion and reducing lumpiness.

Therefore, I recommend using a sawtooth/dispersion blade with your overhead stirrer to disperse the Silica Dimethyl Silylate in your oil phase.

Your reading about needing very high shear like a Rotor-Stator homogenizer is correct. That type of equipment provides very high shear, suitable for dispersing very difficult powders or achieving extremely fine dispersions. However, an overhead stirrer with a sawtooth blade can provide sufficient shear for dispersing Silica Dimethyl Silylate in most lip gloss formulas if done correctly.

Regarding the Sensient sample formula using a propeller for 3.5% Silica Dimethyl Silylate, it's possible that:

1. The formula uses a special grade of Silica Dimethyl Silylate that is easier to disperse.
2. Other dispersing agents are used in the formula.
3. Even with a propeller, the mixing time might be very long, or a very high speed is used.
4. The resulting dispersion might not be as fine as one achieved with true high shear.

Recommendations for dispersing Silica Dimethyl Silylate in oil using an overhead stirrer with a sawtooth blade:

1. Add Silica Dimethyl Silylate gradually to the oil: Slowly sprinkle the powder into the oil while stirring at low to medium speed to prevent large lumps from forming initially.
2. Increase stirring speed: After all the powder is added, increase the speed of your overhead stirrer using the sawtooth blade to generate high shear and break down/dispersing the particles.
3. Stir at high speed for sufficient time: The time required depends on the batch size and stirrer speed. It may take several minutes to ensure complete dispersion. Observe that the liquid is becoming clearer and free of powder lumps.
4. Reduce speed to de-aerate: Once dispersed, significantly reduce the stirring speed or use very slow stirring to help larger air bubbles rise and dissipate. Small air bubbles may take time to disappear on their own, or other techniques like using vacuum might be needed if available.

Reducing Air Bubbles:

• Try to stir without creating a deep vortex that pulls air from the surface into the oil.
• Add the powder slowly and stir at low speed in the initial step.
• After dispersion, continue stirring at a very low speed for an extended period.
• If a vacuum source is available, applying vacuum is very effective for removing air bubbles.

In summary, using a sawtooth/dispersion blade with your overhead stirrer is a suitable method for dispersing Silica Dimethyl Silylate in your lip gloss formula, and high shear should be applied during the dispersion phase before reducing speed for de-aeration.