SILICA DIMETHYL SILYLATEA grade-specific Safety Data Sheet (SDS) — with the complete hazard classification, handling precautions, and transport information — is supplied with every shipment and available on request. Confirm all safety and regulatory details against the SDS for your specific grade.
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Hydrophobic fumed silica is a surface-treated (dimethyl-silylate) fumed silica — a high-performance rheology, anti-settling and reinforcing additive with water-repellent, moisture-resistant behavior. Identity: CAS 68611-44-9.
What it is
This product (CAS 68611-44-9, dimethyl-silylate-treated SiO2) is a fumed silica whose surface silanols have been capped with dimethylsilyl groups, making it hydrophobic. The treatment improves moisture resistance and compatibility with non-polar systems.
Industrial uses
It is used for thixotropy and anti-sag/anti-settling control in coatings, inks, adhesives and sealants (especially solvent-borne and reactive systems), reinforcement and clarity control in silicone rubber (HTV/RTV), anti-caching/free-flow in powders needing moisture resistance, and as a defoamer component. The hydrophobic surface suits systems where standard hydrophilic silica would absorb moisture.
Related: precipitated silica.
Forms, grades and handling
Hydrophobic fumed silica is supplied as a light, low-bulk-density powder in bags; grade is defined by surface area and treatment. Properties are typical reference values; the Certificate of Analysis (CoA) for the lot you buy governs. Always consult the current Safety Data Sheet (SDS) before handling, and confirm regulatory status and suitability for your application and jurisdiction. Each lot ships with CoA, TDS and SDS.
Bulk supply and RFQ
RawSource sources Hydrophobic Fumed Silica direct from producers in bulk, with CoA, TDS and SDS per lot. Tell us the grade, particle size or specification and quantity you need, and we will quote it. Products are sold for industrial and professional use.
Typical Properties
Typical reference values, not a specification; the Certificate of Analysis (CoA) for the lot governs.
| Property | Typical Value |
|---|---|
| Chemical / class | Treated fumed silica |
| CAS Number | 68611-44-9 |
| Molecular Formula | SiO2 (dimethyl-silylate-treated) |
| Handling | Refer to the current SDS |
Frequently Asked Questions
What is hydrophobic fumed silica used for?
Hydrophobic (dimethyl-silylate-treated) fumed silica (CAS 68611-44-9) is used for thixotropy and anti-settling in coatings, inks, adhesives and sealants, reinforcement in silicone rubber, moisture-resistant free-flow in powders, and as a defoamer component. RawSource supplies it for industrial use.
Why use hydrophobic instead of hydrophilic fumed silica?
The dimethyl-silylate surface treatment makes the silica water-repellent, improving moisture resistance, rheology stability and compatibility in non-polar and reactive systems where hydrophilic silica would pick up water.
How is bulk hydrophobic fumed silica supplied and quoted?
RawSource supplies hydrophobic fumed silica in bulk with CoA, TDS and SDS per lot. Pricing is quote-based on grade, particle size/specification and volume; submit an RFQ with your application and quantity.
Disclaimer. Information on this page — including chemical properties, identifiers, hazard, transport (DOT/UN) and tariff (HS) classifications, and applications — is provided for general reference and is compiled from authoritative public sources (e.g. PubChem). Values are typical and are not a guaranteed specification; the Certificate of Analysis (CoA) for the lot you purchase governs. Products are sold for industrial and professional use only. Nothing here is a medical, health, or efficacy claim, or advice. Always consult the current Safety Data Sheet (SDS) before handling, storage, transport or disposal, and confirm regulatory status, classification and suitability for your application and jurisdiction. Hazard, transport and tariff classifications must be verified for your specific shipment. RawSource makes no warranty, express or implied, and assumes no liability for use of this information.