Basic Properties and Mechanism of Action of Fumed Silica
Fumed silica (silicon dioxide) is an inorganic nanomaterial primarily used as a reinforcing agent in silicone rubber. Based on the manufacturing process, fumed silica can be divided into two types: fumed silica and precipitated silica. Fumed silica has characteristics such as small particle size (10-40 nm), large specific surface area (150-380 m²/g), and high purity, and its reinforcing effect is significantly superior to that of precipitated silica.

In silicone rubber, the mechanism of action of fumed silica mainly includes:
Hydrogen bonding: The silanol groups (-Si-OH) on the surface of fumed silica can form hydrogen bonds with the silicone rubber molecular chains, enhancing interfacial bonding force.
Three-dimensional network structure: Nanoscale fumed silica particles form a three-dimensional network structure in the rubber matrix, effectively transferring stress.
Interface optimization: Surface modification can improve the compatibility of the filler-matrix interface and enhance mechanical properties.
Influence of Fumed Silica on the Transparency of Silicone Rubber
The addition of fumed silica significantly affects the transparency of silicone rubber. The main influencing factors include:

Fumed silica quality: Fumed silica has less impact on transparency than precipitated silica due to its more uniform particle size.
Dispersibility: Poor dispersion leads to increased light scattering and reduced transparency.
pH value: Acidic environments (pH < 5.5) can cause silicone rubber to yellow, affecting visual appearance.
Metal impurities: Metal ions such as iron and chromium can catalyze oxidation reactions leading to yellowing.
Studies have shown that by controlling the amount of fumed silica added (usually not exceeding 50 parts), optimizing the dispersion process, and using surface treatment agents (such as hexamethyldisilazane), it is possible to maintain good transparency while preserving mechanical properties. Mechanical Performance Enhancement Mechanism
Fumed silica significantly enhances the mechanical properties of silicone rubber:
Tensile strength: Fumed silica can increase the tensile strength of silicone rubber from 0.38 MPa to 16.23 MPa, an increase of 42.7 times.
Wear resistance: Nanoparticles effectively disperse stress, improving the wear resistance of the material.
Elastic recovery: The three-dimensional network structure helps improve compression deformation rate and elastic recovery.
The optimal addition amount is usually between 40 and 50 parts. Excessive addition can lead to agglomeration, which reduces mechanical properties.

Industrial Applications and Process Control
In actual production, fumed silica-reinforced silicone rubber is widely used in:
Wire and cable insulation layers
Automotive seals
Electronic component encapsulation
Medical devices

Summary
Fumed silica plays a dual role in silicone rubber, simultaneously regulating transparency and enhancing mechanical properties. Due to its excellent nano-characteristics and surface activity, fumed silica is an ideal choice for high-performance silicone rubber. By precisely controlling the addition amount, optimizing the dispersion process, and surface treatment, significant improvements in mechanical properties can be achieved while maintaining good transparency. Future research can further explore new surface modification technologies and composite filler systems to balance the needs of transparency and mechanical performance.