The Role of Fumed Silica in Transparent Sealants
Fumed silica is a nano-sized silica material that plays the following main roles in transparent sealants:

Reinforcing Effect: Significantly improves the mechanical strength and tear resistance of the sealant. The tensile strength of unreinforced silicone rubber is only 0.4 MPa, which can be increased by 40 times after reinforcement with fumed silica.

Thixotropic Thickening: Increases viscosity by forming a network structure, improving workability and preventing sagging and settling.

Optical Properties: With a refractive index of n20/D 1.544 (lit.), combined with the flame retardancy of silicone, it can achieve a semi-transparent flame-retardant effect.

Stability Improvement: Adding anti-settling agents and coupling agents can improve storage stability and prevent oil seepage.
Mechanism of Fumed Silica's Influence on Optical Properties

Scattering Effect: Nano-sized particles (10-20 nm) scatter light, changing the propagation path and affecting transparency. **Refractive Index Matching:** When particle size is moderate and uniformly dispersed, the overall refractive index of the material can be adjusted to reduce light reflection.

**Porous Structure:** Porous structures can capture infrared light waves and reduce reflectivity, but their impact on visible light transparency requires specific analysis.

**Specific Surface Area Influence:** A larger specific surface area (e.g., 200 m²/g) generally results in better transparency, but viscosity will also increase accordingly.

**Optical Influence Control Methods and Techniques:**
1. **Dispersion Process Optimization:**
**Equipment Selection:** Use a high-speed shear disperser (linear speed 10-20 m/s) for low-viscosity systems, and a sand mill or three-roll mill for high-viscosity systems.
**Dispersion Method:** Use a "donut" dispersion pattern to avoid over-dispersion leading to particle re-agglomeration.
**Temperature Control:** Warm the components to 20-25℃ for 2-4 hours before mixing.

2. **Parameter Control:**
**Addition Amount:** It is recommended not to exceed 5-7%, otherwise viscosity will increase and transparency will decrease. Particle size selection: 10-20nm nanoparticles help improve transparency.
Specific surface area: 200 m²/g provides the best overall performance.

3. Surface treatment technology: Silane coupling agents are used to improve the compatibility between the filler and the matrix.
Anti-settling agents are added to improve storage stability.
Hydrophobic products are more difficult to disperse than hydrophilic products and require special treatment.