Fomed silica (fumed silica), as a nanoscale inorganic material, has a significant effect on improving the scratch resistance of nanocoatings. The following is a comprehensive analysis from the aspects of its mechanism of action, addition ratio, performance enhancement effect, formulation examples, and preparation process.

Mechanism of Action of Fumed Silica in Nanocoatings
Fomed silica enhances the scratch resistance of nanocoatings through multiple mechanisms:
**Three-Dimensional Network Structure Formation:** Untreated fumed silica contains a large number of hydroxyl groups on its surface. In oily systems, these hydroxyl groups associate through hydrogen bonds to form a uniform three-dimensional network structure, which can increase the viscosity of the coating. This structure is disrupted by mechanical shear forces, causing a decrease in viscosity; it recovers spontaneously after the shear force is removed.

**Nanoscale Filling Effect:** The primary particle size of fumed silica is between 7-40 nm, and the aggregate particle size is approximately 200-500 nm. It can fill the microscopic voids in the coating, improving the density and hardness of the coating.
**Enhanced Crosslinking Density:** Fumed silica has high surface activity and can form hydrogen bonds with the substrate, enhancing the crosslinking network structure of the coating and thus improving mechanical properties and chemical corrosion resistance.
**Rheology Control:** The excellent rheology control effect of fumed silica can effectively increase the viscosity of the coating, improve its thixotropy, and ensure the uniformity and aesthetics of the coating.
**Typical Addition Ratio of Fumed Silica:** The addition ratio of fumed silica varies in different coating systems:
**Acrylic Coatings:** The optimal addition amount of hydrophilic fumed silica HL-200 is 1.8%, at which point acrylic coatings with a thickness of 275μm do not exhibit sagging.
**Epoxy Coatings:** The optimal addition amount of hydrophobic fumed silica HB-139 is 0.8%.
**Rubber Products:** Adding 10-25 parts of fumed silica to rubber formulations can significantly improve cut resistance.
**Defoamer Formulation:** The addition amount of fumed silica is typically 3-15%, depending on the formulation requirements.
**Scratch Resistance Enhancement:** Fumed silica enhances the scratch resistance of nano-coatings primarily through:
**Increased Hardness:** Fumed silica significantly increases the hardness of the coating, thereby enhancing scratch resistance.
**Improved Abrasion Resistance:** The microparticles of fumed silica fill the voids in the coating material, forming a uniformly dispersed structure and reducing wear.
**Tear Resistance:** Adding fumed silica to silicone rubber significantly improves tear resistance.
**Enhanced Mechanical Properties:** Fumed silica improves the strength and toughness of rubber materials, increasing tear resistance.
**Aging Resistance:** Fumed silica absorbs ultraviolet light, converting its energy into heat, reducing the risk of coating aging.