SEMISIL R272 Fumed Silica (Hydrophobic, Hexamethyldisilazane Treated)
Key Features
- Highest hydrophobicity: 55–65% methanol wettability from complete HMDS capping
- Ultra-low moisture content (<0.3%) — critical for NCO and anhydride-sensitive systems
- Superior thixotropy in non-polar solvents, silicone fluids, and mineral oils
- Excellent compatibility with aliphatic PU, silicone, and alkyd systems
- Aerosil R972 equivalent — verified drop-in replacement from Semitech
SEMISIL R272 is a premium hydrophobic fumed silica from Shanghai Semitech New Material Co., Ltd., produced by treating high surface area fumed silica with hexamethyldisilazane (HMDS). The HMDS treatment reacts with and caps essentially all surface silanol groups with trimethylsilyl (-Si(CH₃)₃) groups, creating a highly hydrophobic surface with extremely low residual silanol content and outstanding moisture barrier performance.
The complete silanol capping of SEMISIL R272 achieves methanol wettability of 55–65%, among the highest hydrophobicity levels available in commercial fumed silica. This ultra-hydrophobic character makes SEMISIL R272 the first-choice thixotropic additive for systems that are critically sensitive to moisture or that are inherently non-polar in character. One-component polyurethane prepolymers with long NCO content, 1K silane-terminated polymers, anhydride-cured epoxy systems, and solvent-free solvent-borne polyester coatings all benefit from SEMISIL R272's moisture-free rheology modification.
In addition to moisture resistance, the trimethylsilyl-capped surface provides excellent compatibility with non-polar and medium-polarity matrices including mineral oils, synthetic lubricants, silicone fluids, aliphatic polyurethanes, and solvent-borne alkyd systems. SEMISIL R272 is the direct equivalent of Evonik Aerosil R972, the world's most recognized hydrophobic fumed silica benchmark.
Specifications
| Parameter | Value |
|---|---|
| Particle type | Highly hydrophobic |
| Carbon content | 0.6–1.2% |
| Tapped density | ≤ 120 g/L |
| BET surface area | 90–130 m²/g (post-treatment) |
| Surface treatment | Hexamethyldisilazane (HMDS) |
| SiO₂ content (approx.) | ≥ 99.0% |
| pH (4% in water/ethanol 1:1) | 5.5–8.5 |
| Moisture content (105°C, 2h) | ≤ 0.3% |
| Hydrophobicity (methanol wettability) | 55–65% methanol in water |
Applications
FAQ
SEMISIL R272's surface is predominantly trimethylsilyl-capped with minimal residual silanol groups. Thixotropy in non-polar systems is achieved primarily through weak van der Waals interactions between the methyl surface groups of adjacent silica aggregates at rest, forming a loose physical network. Under shear, this network breaks apart. Recovery is slower than for hydrophilic grades, which suits applications like non-drip lubricant greases and one-coat horizontal mastics.
Direct Contact
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