Fumed silica is a high-performance material widely used in coatings, adhesives, sealants, silicone rubber, inks, and composites. Depending on the production process and surface treatment, fumed silica can exhibit very different properties.
Two common routes involve the use of Silicon Tetrachloride (STC) and Methyltrichlorosilane (MTCS) as raw materials. Understanding the difference between these two types of fumed silica can help manufacturers select the most suitable product for their applications.
STC (Silicon Tetrachloride, SiCl₄) is the traditional raw material used to produce fumed silica through flame hydrolysis.
The resulting product is typically hydrophilic fumed silica, characterized by a large number of hydroxyl (Si-OH) groups on the surface.
High specific surface area
Excellent thickening and reinforcing properties
Strong hydrogen bonding capability
Good dispersion in polar systems
Suitable for coatings, inks, silicone rubber, and resins
Typical examples include AEROSIL® 200 and similar grades.
MTCS (Methyltrichlorosilane, CH₃SiCl₃) introduces methyl groups during the production process. As a result, the silica surface becomes inherently hydrophobic.
This type of fumed silica is often referred to as hydrophobic fumed silica.
Excellent water repellency
Low moisture absorption
Improved dispersion in non-polar systems
Enhanced anti-settling performance
Better stability under humid conditions
MTCS-derived fumed silica is widely used in sealants, adhesives, RTV silicone, thermal insulation materials, and waterproof coatings.
| Property | STC-Based Fumed Silica | MTCS-Based Fumed Silica |
| Surface Character | Hydrophilic | Hydrophobic |
| Surface Groups | Si-OH | Si-CH₃ |
| Moisture Absorption | High | Very Low |
| Water Resistance | Limited | Excellent |
| Polar System Compatibility | Excellent | Moderate |
| Non-Polar System Compatibility | Moderate | Excellent |
| Typical Applications | Paints, Inks, Rubber | Sealants, Adhesives, Waterproof Systems |
If your formulation requires strong thickening effects in polar systems, STC-based hydrophilic fumed silica is usually the preferred option.
However, if water resistance, moisture protection, and compatibility with non-polar systems are critical, MTCS-derived hydrophobic fumed silica can provide superior performance.
In many advanced adhesive and sealant applications, MTCS-modified fumed silica has become the preferred choice due to its excellent rheology control and long-term stability.
Zhengzhou Gesee New Material Co., Ltd. specializes in the development and supply of high-quality fumed silica products for global customers.
Our portfolio includes both hydrophilic and hydrophobic fumed silica grades, offering reliable alternatives to leading international brands for applications in adhesives, sealants, coatings, silicone rubber, and composite materials.
If you are looking for cost-effective fumed silica solutions, feel free to contact GESEE for technical support and product recommendations.
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