Match any formulation challenge to the right SEMISIL grade and loading level in one lookup — covering 30 application categories across coatings, adhesives…
Match any formulation challenge to the right SEMISIL grade and loading level in one lookup — covering 30 application categories across coatings, adhesives, sealants, and composites.
Fumed silica controls sag resistance and flow behavior through hydrogen-bonded particle networks that break under shear and rebuild at rest. For unsaturated polyester gelcoats, SEMISIL 200 (200 m²/g BET) at 1.0–2.0 wt% delivers thixotropic index values of 4–6 without grinding. Epoxy adhesives typically need SEMISIL 380 (380 m²/g) at 2–4 wt% because higher surface area builds viscosity faster at lower loading. Silicone sealants require hydrophobic grades — SEMISIL R272 (100 m²/g, DDS-treated) at 3–5 wt% prevents moisture-triggered reagglomeration during storage.
Anti-settling performance depends on building a low-shear yield stress that suspends dense pigments (TiO₂ at 4.2 g/cm³, ZnO at 5.6 g/cm³) without raising high-shear viscosity. SEMISIL 150 (150 m²/g) at 0.5–1.5 wt% is the workhorse for solvent-borne industrial primers — it creates a weak gel network at rest while adding under 50 mPa·s at 1000 s⁻¹ shear rate. Waterborne systems need hydrophilic grades pre-dispersed at high shear; SEMISIL 200 at 1.0–2.0% works when added to the mill base before letdown.
Fumed silica reinforces elastomers and composites by creating covalent and physical crosslinks with the polymer matrix. In HTV silicone rubber, SEMISIL 300 (300 m²/g) at 15–40 phr raises tensile strength from 2 MPa (unfilled) to 8–12 MPa while maintaining elongation above 300%. The reinforcement mechanism requires high BET surface area for maximum polymer–filler interaction. For epoxy composites, 1–3 wt% of S-200 increases fracture toughness (K_IC) by 30–60% through crack deflection without raising viscosity beyond processable limits.
Hydrophobic fumed silica grades prevent moisture absorption and improve powder flowability. SEMISIL R272 (DDS-treated, 100 m²/g post-treatment BET) reduces the angle of repose of hygroscopic powders from 45° to below 30° at just 0.2–0.5 wt% loading. For toner production, H-150 at 0.5–1.0% controls triboelectric charge while preventing blocking at 40°C/90% RH storage conditions. The choice between DDS and HMDS surface treatments depends on the carrier solvent — DDS grades disperse better in non-polar systems (hydrocarbons, silicones), while HMDS grades suit moderately polar environments (esters, ketones).
The table below maps 30 common application categories to the recommended SEMISIL starting grade and loading range. Use…
The table below maps 30 common application categories to the recommended SEMISIL starting grade and loading range. Use these as baseline formulations — final optimization depends on your specific resin system, pigment volume concentration, and processing conditions.
| Application Category | Recommended Grade | BET (m²/g) | Loading (wt%) | Primary Function |
|---|---|---|---|---|
| Epoxy structural adhesive | S-380 | 380 | 2–4 | Thixotropy |
| Polyester gelcoat | S-200 | 200 | 1–2 | Anti-sag |
| Silicone RTV sealant | H-150 | 150 | 3–5 | Thixotropy + reinforcement |
| HTV silicone rubber | S-300 | 300 | 15–40 phr | Reinforcement |
| Solvent-borne primer | S-150 | 150 | 0.5–1.5 | Anti-settling |
| Waterborne architectural paint | S-200 | 200 | 1–2 | Anti-settling |
| UV-cure coating | S-200 | 200 | 1–3 | Rheology control |
| Powder coating | S-150 | 150 | 0.3–0.5 | Free-flow / fluidization |
| Polyurethane adhesive | S-200 | 200 | 2–4 | Thixotropy |
| PVC plastisol | S-150 | 150 | 1.5–3 | Rheology control |
| Unsaturated polyester resin | S-200 | 200 | 1–2.5 | Anti-settling + thixotropy |
| Dental composite | S-380 (silanized) | 380 | 5–15 | Reinforcement |
| Pharmaceutical tablet | H-200 | 200 | 0.2–0.5 | Free-flow |
| Toner production | H-150 | 150 | 0.5–1 | Charge control + flow |
| Lithium battery slurry | S-200 | 200 | 0.5–1.5 | Anti-settling |
| Thermal interface material | S-300 | 300 | 2–5 | Thixotropy |
| Cosmetic emulsion | H-200 | 200 | 1–3 | Stabilization |
| Food-grade antifoam | H-150 | 150 | 2–4 | Defoaming |
| Fiberglass SMC/BMC | S-200 | 200 | 1–2 | Low-profile additive support |
| Cable compound | S-200 | 200 | 2–5 | Reinforcement |
| Printing ink (offset) | S-300 | 300 | 1–2 | Anti-misting |
| Flexographic ink | S-200 | 200 | 0.5–1.5 | Viscosity build |
| Marine antifouling paint | S-150 | 150 | 1–2 | Anti-settling |
| Fire extinguisher powder | H-150 | 150 | 0.5–1.5 | Free-flow |
| Crop protection granule | H-200 | 200 | 0.3–0.8 | Anti-caking |
| Epoxy flooring | S-200 | 200 | 1.5–3 | Anti-sag on vertical |
| Gel battery electrolyte | S-300 | 300 | 5–8 | Gelation |
| Ceramic tape casting | S-200 | 200 | 0.5–1 | Binder rheology |
| Lubricating grease | S-150 | 150 | 3–8 | Thickening |
| Polysulfide sealant | S-200 | 200 | 3–6 | Reinforcement + thixotropy |
Start with the grade-loading combination from the matrix, then adjust ±0.5 wt% based on your resin viscosity and pigment density. When in doubt between two grades, choose the higher BET — it builds structure faster at lower loading, reducing material cost per batch.
Use hydrophilic grades (S-series) for polar systems like epoxies, waterborne coatings, and polyester resins where silanol groups hydrogen-bond with the matrix. Switch to hydrophobic grades (H-series) when moisture resistance, long-term storage stability, or non-polar compatibility is required — such as silicone sealants, powder flow aids, and toner.
Start at 1.5 wt% of a 200 m²/g grade as a baseline for most liquid resin systems. Increase by 0.5% increments until the thixotropic index reaches 3.5–5.0. Higher BET grades (300–380 m²/g) achieve the same index at 30–40% lower loading, which offsets their higher per-kg cost.
Higher BET means more particle surface for polymer interaction, which builds viscosity and reinforcement faster per unit weight. However, it also increases dispersion difficulty and can shorten pot life in reactive systems. For simple anti-settling tasks, 150 m²/g is sufficient and far easier to incorporate.
Yes, blending is common in silicone rubber compounding where S-300 provides reinforcement and H-150 controls processing and moisture sensitivity. Pre-mix the grades dry before adding to the polymer. Typical blend ratios range from 70:30 to 50:50 hydrophilic-to-hydrophobic.
Fish-eyes form when dry fumed silica is added after letdown into low-shear conditions, creating hydrophobic micro-aggregates that resist wetting. Always add fumed silica to the mill base or pre-disperse in water using a high-speed disperser at 10–15 m/s tip speed before incorporating into the paint.
Hydrophobic grades carry a 15–30% premium over equivalent hydrophilic grades due to the additional surface treatment step (DDS or HMDS silanization). However, the lower loading needed for some applications — such as free-flow where 0.3% H-grade replaces 0.8% untreated — can make the per-batch cost comparable or lower.
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