Fumed silica achieves rheological control in high-solids coatings primarily through the following mechanisms, the effectiveness of which is closely related to the surface treatment type (hydrophilic/hydrophobic) and the dosage.


I. Core Mechanism
**Three-Dimensional Network Structure Construction:** Untreated fumed silica contains a large number of hydroxyl groups on its surface, forming a three-dimensional network structure through hydrogen bonding, imparting high thixotropy to the coating. When this structure is disrupted by shear force, the viscosity decreases, and it automatically recovers after standing, effectively balancing application flowability and anti-sagging properties.

II. Key Performance Optimization
**Anti-Sagging:** In acrylic and polyurethane coatings, a 1.8% addition of hydrophilic fumed silica can support a 275μm thick coating without sagging.

**Corrosion Resistance:** Acrylic coatings with 1.8% hydrophilic fumed silica showed significantly improved film adhesion after 500 hours of salt spray testing. Application Efficiency: As an external additive in powder coatings, it improves particle flowability and reduces agglomeration.

III. Application Recommendations
Type Selection: For highly polar systems (such as epoxy resins), hydrophobic fumed silica is recommended to avoid hydrogen bond failure due to solvent effects.

Dosage Optimization: Adjustments need to be made based on the resin system. For example, the optimal dosage of hydrophobic fumed silica in epoxy coatings is 0.8%.

Fomed silica significantly improves the application stability and coating durability of high-solids coatings through precise control of rheological properties, making it an indispensable functional additive for such coatings.