Silicone rubber (whether high-temperature vulcanizate (HTV) or liquid latex (LSR)) formed solely from raw rubber vulcanization typically has extremely low strength, breaking easily under stress and rendering it practically useless. Hydrophobic fumed silica, as a core reinforcing filler, fundamentally transforms the fragile silicone rubber matrix into an elastomer material with high tear resistance and tensile strength.

This significant leap in mechanical properties stems from the powerful physical interaction between nanoscale silica particles and polymer chains. Fumed silica possesses an extremely high specific surface area (typically above 200 m²/g). When hydrophobic silica is dispersed in silicone rubber, its surface siloxane groups are highly compatible with the rubber molecular chains. During mixing and vulcanization, the rubber molecular chains are tightly adsorbed onto the surface of the nanoparticles, forming a layer of "bound rubber." This adsorption is equivalent to introducing countless mobile physical cross-linking points into the polymer network.

When vulcanized silicone rubber is stretched by an external force, the molecular chains adsorbed on the particle surface orient and extend. Due to the strong interaction between the particles and the matrix, the external force can be effectively transferred from the flexible rubber matrix to the rigid silica framework. Furthermore, during crack propagation, these nanoparticles can also hinder crack extension, consuming a large amount of fracture energy by inducing crazing or shear banding. This "pinning effect" significantly improves the material's tear resistance, preventing catastrophic failure under stress.

Hydrophobic treatment plays a role in optimizing interfacial bonding during this process. Compared to hydrophilic silica, hydrophobic modification reduces the polar hydroxyl groups on the particle surface, eliminating the tendency for particle aggregation and allowing for more uniform dispersion as native particles. Uniform dispersion means more effective interfacial area participates in stress transfer, thereby improving tensile strength while maintaining the excellent transparency and resilience of silicone rubber, avoiding stress concentration points caused by filler agglomeration.a