What is fumed silica?
Fumed silica is a highly dispersed, amorphous and extremely pure silica. It is prepared by high-temperature hydrolysis of silicon tetrachloride under a hydrogen-oxygen phase flame. Its primary particles are Spherical particles with no holes inside. Primary particles interact and aggregate within the flame, forming aggregates. The average particle size of primary particles ranges from 7nm to 40nm, and the corresponding specific surface area is 150 to 400m2/g. Siloxane and silanol groups are located on the surface of fumed silica particles. The presence of the latter makes untreated fumed silica hydrophilic.

Hydrophobic fumed silica
Fumed silica can be surface modified by reacting silanol groups with suitable compounds. Hydrophilic and hydrophobic fumed silicas have been successfully used in many fields. Gas silicon can play the following roles in customer products:
• Reinforcing fillers
• Thickeners and thixotropic agents
• Anti-settling agent
• Free flow additives

How to choose gas silicon
1. Select by system polarity
The difference in polarity can bring better dispersion effect to the gas silicon, so that the performance of the gas silicon can be fully reflected.
2. Select according to the comparison table
The same kind of gas silicon: the larger the specific ratio, the greater the thickening, the better the thixotropy, the worse the extrudability, the greater the dispersion difficulty, and the better the transparency;
If it is a product that requires cross-linking, such as adhesives, the tensile strength and tear resistance of the finished product after cross-linking will be greater; the elongation at break and hardness will have little effect.
3. Select according to the required system viscosity
When adding gas silicon, it is often encountered that the viscosity is suitable when the addition amount is low, but the reinforcement is not enough. After increasing the addition amount, although the reinforcement is satisfied, the system viscosity is too high. At this time, we can change some of the original added hydrophilic silica to hydrophobic products.
This is because the higher the hydrophobicity of gas silicon: the worse the thickening property, the worse thixotropy, the better the extrudability, the better the transparency, and the better the dispersion quality.
If it is a product that requires cross-linking, such as adhesives, the mechanical properties of the finished product after cross-linking will not be affected by the degree of hydrophobization.
Therefore, hydrophobic products can play a certain role as viscosity regulators in the system: they can bring a wider viscosity range to the product without affecting the mechanical properties of the final product.
4. Consider the impact of the added amount of gas silicon on product performance.
The same type of silicone: the greater the amount added, the lower the transparency, the thickening, the lower the extrudability, and the harder it is to disperse; after cross-linking, the tensile strength and tear resistance of the finished product are significantly enhanced, the hardness is slightly increased, and the elongation at break is There is no significant impact on resilience.