Hydrophobic Fumed Silica Series

Engineered surface treatments (HMDS, DDS, PDMS) providing ultimate rheology control, moisture resistance, and mechanical reinforcement for advanced industrial applications.

Grade Selection Matrix

Compare our hydrophobic fumed silica treatments to find the exact match for your formulation.

Grade	Treatment	BET (m²/g)	Carbon Content	Primary Advantage
SemiSIL R620	HMDS	200 ± 20	1.5% - 2.1%	LSR clarity & tear strength.
SemiSIL R272	DDS	110 ± 20	0.6% - 1.2%	RTV stability & shelf-life.
SemiSIL R202	PDMS	100 ± 20	3.5% - 5.5%	HCR anti-structuring & rheology.

SemiSIL R620: HMDS Treated

Based on a high-surface-area 200 m²/g carrier, SemiSIL R620 provides high hydrophobicity and superior mechanical reinforcement. It is the gold standard for transparent LSR and HTV silicone rubber systems.

LSR & HTV Rubber

Acts as a powerful reinforcing filler, boosting tear strength while maintaining the highest optical clarity.

High-End Coatings

The ideal anti-settling agent, preventing pigment sedimentation in clear coats without affecting transparency.

Technical Powders

Serves as an advanced anti-caking aid for sensitive powders, providing superior fluidization and moisture protection.

Adhesives & Inks

Ensures stable thixotropy for structural adhesives and inks, allowing for high-build applications with zero sagging.

SemiSIL R272: DDS Treated

Optimized for moisture-sensitive formulations, this DDS treated fumed silica acts as a superior long shelf-life thixotropic agent, preventing viscosity drift in RTV silicone sealants.

RTV Silicone Sealants

Ensures a 24-month shelf-life by preventing viscosity drift and maintaining stable thixotropy in the tube.

Printing Inks

Keeps pigments in permanent suspension while ensuring optimal flow during high-speed printing.

Adhesives & Sealants

Delivers precise rheology control for RTV-T adhesives, providing excellent non-sag properties for vertical joints.

Powder Coatings

Serves as a high-performance free flow aid, protecting particles from humidity-induced clumping in spray booths.

SemiSIL R202: PDMS Treated

Engineered for maximum moisture resistance. By chemically bonding silicone oil to the silica surface, R202 eliminates the "structuring" effect in rubber and ensures consistent viscosity in polar resins.

Silicone Rubber (HCR)

Functions as a premier anti-structuring agent, shielding reactive silanols to prevent crepe hardening during storage.

Epoxy Resins

Provides superior rheology control in polar systems like epoxy and vinyl ester, ensuring zero viscosity drop over time.

Cable Gels

The essential hydrophobic silica for fiber optic cable gels, offering an ultimate moisture barrier and stable dielectrics.

Structural Coatings

Acts as an elite rheology modifier, creating a robust 3D network that ensures perfect anti-sagging for vertical structural coatings.

Technical FAQ: Selecting the Right Hydrophobic Grade

What is the difference between HMDS, DDS, and PDMS treated silica?

The choice depends on your chemical environment. HMDS treated fumed silica (R620) uses hexamethyldisilazane for high clarity and reinforcement. DDS treated fumed silica (R272) uses dimethyldichlorosilane for long-term stability, while PDMS treated fumed silica (R202) utilizes silicone oil for maximum moisture shielding and anti-structuring.

How do I prevent "crepe hardening" and extend sealant shelf-life?

For HCR silicone rubber, use SemiSIL R202 as a premier anti-structuring agent for silicone rubber. For RTV systems, SemiSIL R272 acts as a shelf-life stabilizer for RTV sealants, preventing viscosity drift and ensuring the product remains thixotropic for up to 24 months.

Is surface modified fumed silica effective for powder coatings?

Yes. As a surface modified fumed silica, these grades provide specialized functionality. Use them as an anti-caking aid for powder coatings to prevent moisture clumping, or as a non-sag agent for vertical joint adhesives and high-build printing inks to ensure zero slump.

Which grade is best for water repellent silica and LSR clarity?

For extreme moisture protection, water repellent silica like R202 (PDMS) is essential for cable gels. However, if your goal is high transparency fumed silica for LSR, the HMDS treatment in R620 offers the best refractive index compatibility while maintaining superior tear strength.

When should I specify a hydrophobic silica with 200 BET?

Choose a hydrophobic silica with 200 BET (R620) when maximum mechanical reinforcement is required. If your formulation is sensitive to high organic loading, a low carbon content hydrophobic silica like R272 (DDS) provides the necessary hydrophobicity without over-saturating the system with methyl groups.

Request Free Samples & Technical Advice

Tell us about your formulation. Our technical team from the Anhui R&D Center will match you with the right grade and dispatch samples within 48 hours.