Rheology & Reinforcement
Key Capabilities
- Thixotropy & Viscosity Control:Creates a robust 3D hydrogen-bonding network that provides excellent sag resistance and viscosity build-up in liquids.
- Ultimate Reinforcement: Dramatically enhances tensile strength, tear resistance, and elongation in HTV and RTV silicone rubber.
- Anti-Settling & Anti-Caking: Prevents pigment sedimentation in liquid coatings and acts as a premium free-flow agent in powder systems.
- Exceptional Optical Clarity: Nano-scale primary particles ensure zero optical haze in sensitive transparent formulations and clear resins.
Primary Applications
- RTV Sealants & Adhesives
- HTV & LSR Silicone Rubber
- Coatings, Paints & Printing Inks
- CMP Slurries & Gel Electrolytes
- Defoamers & Powder Coatings
Grade Selection Matrix
Compare our hydrophilic fumed silica parameters to find the precise grade for your manufacturing needs. Selection is primarily driven by the required BET Surface Area and specific shear capabilities.
| Grade | Spec | Primary Advantage | Notes |
|---|---|---|---|
| SEMISIL® 150 | BET 150 ± 25 m²/g | Lowest viscosity impact & rapid dispersion. | Engineered for maximum dispersibility. Allows for significantly higher filler loading in liquid systems (like defoamers) without excessive viscosity build-up. Also serves as an exceptional anti-caking agent for powders. |
| SEMISIL® 200 | BET 200 ± 25 m²/g | Universal thixotropy & shelf stability. | Our flagship grade. Provides superior molecular stability, anti-sagging, and rheology control for general coatings and adhesives. Highly effective for reinforcing standard silicone rubber. |
| SEMISIL® 300 | BET 300 ± 25 m²/g | Exceptional tear resistance & optical clarity. | Creates a powerful 3D network acting as the ultimate reinforcement filler for HTV silicone. Ensures zero optical haze in transparent coatings and delivers sharp print definition in high-speed inks. |
| SEMISIL® 380 | BET 380 ± 30 m²/g | Maximum thickening efficiency & precision. | The highest surface area grade. Creates a highly dense 3D network at minimal dosages. The preferred choice for nano-scale CMP slurries and ultra-clear LSR (Liquid Silicone Rubber) parts. |
💡 Formulator Tip: Higher BET surface area (e.g., 300/380) provides exponential thickening power and clarity but requires high-shear equipment to fully disperse. For standard low-shear mixing or high solid-loading systems, start with 150 or 200.
General Properties (Hydrophilic Series)
Typical physico-chemical data across the SEMISIL® hydrophilic portfolio. Produced under stringent controls ensuring exceptional purity (≥99.8% SiO₂).
| Properties & Test Methods | Typical Value | Unit |
|---|---|---|
| pH Value (in 4% dispersion) | 3.6 ~ 4.5 | – |
| Loss on Drying (2h @ 105°C) | ≤ 1.5 | Wt% |
| Loss on Ignition (2h @ 1000°C)* | ≤ 2.5 | Wt% |
| Sieve Residue (45 µm) | ≤ 0.05 | % |
| Silica Content (based on ignited material) | ≥ 99.8 | Wt% |
| Tamped Density* | 40 ~ 60 | g/L |
| Carbon Content* | ≤ 0.2 | Wt% |
- Based on material dried for 2 hours at 105°C. All test methods comply with GB/T20020 standardization.
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Frequently Asked Questions
Rheology and reinforcement solutions from our R&D engineers.
+How does the BET surface area affect thickening and thixotropy?
The thickening power of fumed silica is directly proportional to its BET surface area. SEMISIL 380 has the highest surface area, meaning it has the most silanol groups available to form a dense 3D hydrogen-bonding network, providing maximum viscosity build and sag resistance at very low dosages. Conversely, SEMISIL 150 offers a weaker network, allowing for higher volume loading without making the fluid too thick.
+What equipment is needed to disperse fumed silica properly?
Because fumed silica forms strong agglomerates, it requires proper shear forces to break down to its primary nano-particles. While SEMISIL 150 and 200 can often be dispersed with high-speed dissolvers (Cowles blades), the higher surface area grades like SEMISIL 300 and 380 typically require rotor-stator systems, bead mills, or three-roll mills to achieve their full rheological and optical potential.
+Will hydrophilic fumed silica affect the transparency of clear resins?
When properly dispersed, fumed silica is highly transparent in most polymer systems because its primary particle size (7-40 nm) is smaller than the wavelength of visible light. For ultimate optical clarity (such as in clear LSR or premium wood coatings), SEMISIL 300 and 380 are the preferred choices due to their ultra-fine primary particles.
+When should I use hydrophilic vs. hydrophobic fumed silica?
Hydrophilic fumed silica is generally used in non-polar to medium-polar systems (like silicone rubber, mineral oils, and certain resins) where it can easily form hydrogen bonds. If your system is highly polar (like waterborne epoxies or epoxy-rich adhesives), the hydrophilic silica will bond with the liquid rather than itself, losing its thickening power. In such highly polar systems, you must switch to our SEMISIL Hydrophobic Series.
Series Selection Summary
In summary, the SEMISIL® Hydrophilic Series provides a versatile toolkit for rheology mastery. Whether you require the high-loading capacity of SEMISIL 150 or the extreme reinforcement and clarity of SEMISIL 380, our high-purity synthetic silica ensures consistent performance across coatings, adhesives, and silicone elastomers.