SEMISIL R202 Fumed Silica (Hydrophobic, DDS Treated)
Key Features
- DDS surface treatment provides excellent hydrophobicity (≥40% methanol wettability)
- Very low moisture uptake (<0.5%) — ideal for 1K moisture-sensitive formulations
- Effective thixotropy in non-polar and solvent-borne systems
- Better powder handling than hydrophilic grades (less dust, lower bulk density variation)
- Equivalent to Aerosil R202 — drop-in replacement for established formulations
SEMISIL R202 is a hydrophobic fumed silica produced by Shanghai Semitech New Material Co., Ltd. through post-treatment of high surface area hydrophilic fumed silica with dimethyldichlorosilane (DDS). The DDS treatment replaces surface silanol groups with dimethylsilyl groups, converting the particle surface from hydrophilic to hydrophobic. This fundamental surface chemistry change makes SEMISIL R202 the ideal choice for moisture-sensitive resin systems and applications where water contamination must be rigorously excluded.
The hydrophobic surface of SEMISIL R202 prevents the adsorption of atmospheric moisture that is inherent with hydrophilic grades. This is critical in one-component polyurethane systems (1K PU), moisture-cure adhesives, silane-modified polymers, and certain epoxy formulations where even trace water can trigger premature curing, cause foaming, or degrade shelf life. The DDS treatment also reduces the tendency of SEMISIL R202 to form strong agglomerates in dry powder form, facilitating better incorporation.
SEMISIL R202 builds thixotropy in non-polar and medium-polarity systems through steric interactions and residual silanol-based bonding, providing effective rheology control in polyurethane sealants, silicone sealants, hydrophobic epoxy coatings, and solvent-borne systems. Its low moisture absorption ensures consistent performance over extended storage periods. SEMISIL R202 is equivalent to Evonik Aerosil R202.
Specifications
| Parameter | Value |
|---|---|
| Particle type | Hydrophobic |
| Carbon content | 1.5–2.5% |
| Tapped density | ≤ 100 g/L |
| BET surface area | 100–130 m²/g (post-treatment) |
| Surface treatment | Dimethyldichlorosilane (DDS) |
| SiO₂ content (approx.) | ≥ 98.0% |
| pH (4% in water/ethanol 1:1) | 5.0–8.0 |
| Moisture content (105°C, 2h) | ≤ 0.5% |
| Hydrophobicity (methanol wettability) | ≥ 40% methanol in water |
Applications
FAQ
Both SEMISIL R202 and R272 are hydrophobic fumed silicas, but they differ in surface chemistry. R202 uses dimethyldichlorosilane (DDS), creating dimethylsilyl surface groups with residual silanol functionality (partial hydrophobicity). R272 uses hexamethyldisilazane (HMDS), creating trimethylsilyl groups for higher hydrophobicity and more complete silanol capping. R272 is therefore better for extremely moisture-sensitive 1K systems, while R202 is preferred when some polar compatibility is beneficial.
Direct Contact
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