What is Hydrophobic Fumed Silica?
Hydrophobic Fumed Silica (HFS)
Aurexene Materials Hydrophobic Fumed Silica is an 11-grade family of surface-treated synthetic amorphous silica powders for rheology, suspension, anti-sag, reinforcement, and powder-flow control.
Technical owner: Aurexene Materials Engineering Team · Last updated: 2026-08-10
HFShydrophobic silicatreated fumed silicasurface-treated synthetic amorphous silicaanti-sag silica
Quick Answer
Aurexene Materials Hydrophobic Fumed Silica is a surface-treated fumed-silica grade family used to build low-shear structure, improve suspension and anti-sag behavior, reinforce silicone elastomers, and support powder-flow and caking control.
What It Is Not
- Hydrophobic fumed silica is a formulation additive, not a finished adhesive, sealant, coating, ink, elastomer, thermal interface material, or powder blend.
- The grade-family screening ranges below are not guaranteed release specifications; confirm the current grade TDS, COA, test method, and lot before qualification.
When Not to Use It
- Do not select a grade when its surface treatment, residual profile, dust controls, matrix compatibility, or current safety documentation cannot be confirmed for the intended process and market.
Intrinsic Screening Summary
- Identity screen
- Synthetic amorphous silica base with a hydrophobic surface treatment; the family includes PDMS-, DDS-, HMDS-, and D4-treated grades plus two grades whose treatment is not specified in the controlled family data.; Surface-treated fumed-silica powder; exact primary-particle and agglomerate morphology are not specified in the controlled family data.
- Intrinsic feature
- Dispersed particles can form a reversible network whose low-shear structure and recovery depend on surface area, treatment, matrix polarity, loading, dispersion energy, and shear history.
- Material-level integration
- Screen surface treatment, BET area, carbon, pH, and tapped density together.
Application Fit
| Application | Suitability | Conditions | Limitations |
|---|---|---|---|
| Rheology, Suspension & Anti-Sag Control | GOOD FIT | Screen for silicone elastomers, adhesives and sealants, coatings and inks, and dry powder systems where low-shear structure, suspension, anti-sag, reinforcement, flow, or caking control is required. | Select and qualify the exact surface treatment, BET range, loading, dispersion process, rheology method, and storage response in the final formulation. |
| Thermally Conductive & Electrically Insulating Polymers | CONDITIONAL | Developmental rheology and storage-stability aid in silicone formulations containing BN, AlN, or Al2O3 thermal fillers. | No component-level thermal performance or universal loading is supplied; qualify dispensing force, voiding, thermal response, cure, and storage uniformity in the final compound. |
| Electronic Packaging & Interconnects | CONDITIONAL | Developmental rheology and filler-suspension aid in resin or silicone encapsulation systems. | Qualify voids, cure, moisture behavior, electrical properties, contamination controls, reliability cycling, and the exact grade residual profile before package use. |
Selection & Validation Framework
| Decision Question | Material-Level Answer |
|---|---|
| Addition order and dispersion | Establish addition order, dispersion energy, and shear history in a controlled formulation trial. Use the actual silicone, resin, adhesive, coating, ink, or powder system; no grade-specific protocol is supplied. |
| Loading | Set loading experimentally on a stated weight or volume basis. No validated universal loading range is supplied; stop when rheology, dispersion, processability, cure, or final performance leaves acceptance. |
| Process controls | Validate temperature, atmosphere, pH, viscosity, filtration, dust controls, and equipment response in the actual process. |
Material Identity & Specification Status
HFS Grade-Family Formulation Screen
Use these family-level ranges to shortlist grades. They are not guaranteed release specifications; confirm the current grade TDS, COA, methods, and lot before qualification.
| Grade | Surface treatment | BET (m²/g) | Loss on drying | Carbon (%) | pH | Tapped density (g/L) |
|---|---|---|---|---|---|---|
| HD171 | PDMS | 80–120 | ≤0.5% | 4.0–6.0 | 4.5–6.5 | ≈60 |
| HD172 | PDMS | 100–140 | ≤0.5% | 4.5–6.5 | 4.5–6.5 | ≈60 |
| HD161 | DDS | 100–140 | ≤0.5% | 1.0–2.0 | 4.5–6.5 | ≈60 |
| HD162 | DDS | 140–180 | ≤0.5% | 1.0–2.5 | 4.5–6.5 | ≈60 |
| HD163 | DDS | 200–260 | ≤0.5% | 1.4–2.6 | 4.0–7.0 | ≈60 |
| HD151 | HMDS | 90–130 | ≤0.5% | 0.7–1.5 | 5.0–7.0 | ≈60 |
| HD152 | HMDS | 140–180 | ≤0.5% | 1.5–3.0 | 5.0–7.0 | ≈60 |
| HD153 | HMDS | 195–245 | ≤0.5% | 3.0–4.5 | 5.0–7.0 | ≈60 |
| HD106 | D4 | 200–260 | ≤0.5% | 2.0–3.5 | 5.0–7.0 | ≈60 |
| HD805 | Not specified | 130–170 | ≤0.5% | 4.5–6.5 | 3.5–6.0 | ≈60 |
| HD2000G | Not specified | 130–170 | ≤0.6% | 2.5–4.0 | 5.0–7.0 | 100–220 |
Functional Performance
| Property | Value | Conditions |
|---|---|---|
| Rheology and thixotropic recovery | Formulation-dependent; no universal viscosity or yield-value target is claimed. | Measure the full shear-rate profile, low-shear recovery, temperature response, and aging in the final matrix. Surface area alone does not predict finished-formulation rheology. |
| Suspension and anti-sag control | Formulation-dependent; qualify settling, sag, leveling, and dispense behavior together. | Use the final resin, pigment or filler package, loading, dispersion energy, and shear history. Excess structure can impair leveling, pumping, dispensing, mixing, or degassing. |
| Powder flow and caking control | Powder-system dependent; no universal dose or flow index is claimed. | Qualify dustiness, humidity, dosage, blend uniformity, storage, and downstream processing. A flow aid cannot compensate for uncontrolled moisture, segregation, or an incompatible blending process. |
Why It Works
| Structure | Function | Mechanism |
|---|---|---|
| Hydrophobically surface-treated fumed-silica particle network | Low-shear structure, recovery, suspension, anti-sag behavior, reinforcement, and powder-flow control in compatible formulations. | Dispersed particles can form a reversible network whose low-shear structure and recovery depend on surface area, treatment, matrix polarity, loading, dispersion energy, and shear history. |
Compare Material Routes
| Material / Route | Decision Boundary |
|---|---|
| PDMS-, DDS-, HMDS-, and D4-treated HFS grades | Multiple treatment and surface-area families allow compatibility and rheology screens across organic matrices. Treatment name, BET area, carbon, pH, and tapped density are screening variables; final performance and residual requirements must be qualified by grade. |
Failure-Mode Watchouts
| Failure Mode | Trigger | Material-Level Response |
|---|---|---|
| Sag or settling remains uncontrolled | Insufficient structure, incompatible treatment, low effective loading, or a dispersion process that does not build the required network. | Re-screen grade treatment and BET family, then re-optimize loading, addition order, dispersion energy, and conditioning in the final matrix. |
| The formulation becomes difficult to mix, level, pump, dispense, filter, or degas. | Excess structure, unsuitable surface treatment, excessive loading, agglomeration, or unrepresentative shear history. | Reduce or change the HFS route and qualify the full rheology curve, process torque, filtration or nozzle response, and air release. |
| Viscosity, suspension, or powder flow drifts during storage. | Moisture, incomplete dispersion, matrix incompatibility, changing shear history, or uncontrolled conditioning. | Control storage, moisture, mixing history, and aging protocol; compare initial and aged acceptance in the final package. |
Technical Guides
| Technical Guide | Summary |
|---|---|
| Managing High Filler Loading, Viscosity, Mixing Torque, and Moldability | Managing High Filler Loading, Viscosity, Mixing Torque, and Moldability — a method-conditioned engineering guide for Thermally Conductive & Electrically Insulating Polymers covering structure-function behavior at the material, interface, and finished-system boundary, process limits, validation, and qualification boundaries. |
FAQ
How should the 11 HFS grades be compared?
Start with surface treatment, BET surface area, carbon, pH, and tapped density, then qualify the exact grade in the final matrix with controlled loading, dispersion, shear history, and aging.
Is Hydrophobic Fumed Silica a thermal filler?
It is not presented here as the primary heat-conducting filler. In thermal formulations it is a developmental rheology and suspension aid that must be tested with the actual BN, AlN, or Al2O3 filler package.
Documents & Inquiry
Document access follows the current approval state. Unapproved or unavailable files route to a document request instead of a public download.
Technical Data Sheet
Approval required
Safety Data Sheet
Approval required
Hydrophobic Fumed Silica Manufacturing, Grade & Qualification Support
Aurexene Materials helps shortlist HFS grades by matrix, treatment family, surface area, rheology target, sag or settling risk, process window, storage condition, dust controls, and documentation needs.
Hydrophobic Fumed Silica RFQ qualification checklist
- Matrix chemistry, cure route, fillers or pigments, and supplied form:
- Target rheology curve, sag, settling, recovery, leveling, or powder-flow response:
- Mixing, dispersion, addition order, temperature, shear history, filtration, and dispensing process:
- Loading basis, batch size, storage condition, aging time, and package format:
- Required treatment disclosure, residual limits, current TDS, SDS, COA, and market classification:
This inquiry and qualification path does not guarantee performance or availability:
- Define the matrix, application subtype, rheology or powder-flow objective, and process acceptance window.
- Screen treatment family, BET range, carbon, pH, and tapped density without treating family ranges as release specifications.
- Compare shortlisted grades in the final formulation using controlled addition, dispersion, conditioning, and aging.
- Confirm the current grade TDS, SDS, COA, treatment, residual profile, dust controls, and regulatory fit before release.
The family TDS supports formulation screening, not a guaranteed grade specification or finished-system performance claim. Final recommendations require current grade documents and application-level validation.
Review Lab Capabilities for sample evaluation and qualification support, or Production Capabilities for scale-up, quality, documentation, and supply support.
Request Hydrophobic Fumed Silica Sample / Qualification Review