SEMISIL 150 vs 200 vs 300 vs 380 — Choosing the Right Hydrophilic Fumed Silica Grade
Four hydrophilic fumed silica grades spanning 150–380 m²/g BET surface area — each optimized for different viscosity, clarity, and cost trade-offs in industrial formulations.
BET surface area is the single most important parameter when selecting among SEMISIL hydrophilic grades. Moving from SEMISIL 150 (150 m²/g) to SEMISIL 380 (380 m²/g), primary particle diameter shrinks from approximately 12 nm down to 7 nm. Smaller particles mean exponentially more surface silanol groups (Si–OH) per gram — roughly 4–5 OH/nm² across all grades. This directly governs hydrogen-bond network density in liquid media, which is why higher-BET grades build viscosity faster at lower loading levels. For a deeper explanation of how BET drives performance, see our guide on BET surface area explained.
Higher BET grades disperse into finer aggregate structures, but they also scatter more light at visible wavelengths due to increased aggregate networking. In clear-coat and optical adhesive formulations, SEMISIL 150 and 200 maintain haze below 2% at typical anti-settling loadings (1–2 wt%). SEMISIL 300 pushes haze to 3–5% at the same loading, and SEMISIL 380 can exceed 6%. For applications where transparency is critical — UV-cure clear coats, LED encapsulants, display bonding adhesives — SEMISIL 150 or 200 is the correct choice. When clarity is secondary to rheology control (structural adhesives, gel coats), SEMISIL 300 or 380 delivers better cost-performance. See our hydrophilic fumed silica overview for surface chemistry details.
Raw material price per kilogram rises roughly 15–25% from SEMISIL 150 to SEMISIL 380 due to longer flame residence time and lower throughput during pyrogenic synthesis. But cost-per-unit-effect — the price to achieve a target viscosity increment — often favors higher-BET grades. Because SEMISIL 380 requires 40–50% less loading than SEMISIL 150 for equivalent thickening, its effective cost per formulation batch can be 10–20% lower despite the higher unit price. Formulators should calculate total cost of use, not price per kilogram, when comparing grades. Use our BET surface area selection guide to match grade to your specific resin system.
Thickening efficiency scales non-linearly with BET surface area. In a standard epoxy resin at 3 wt% loading, SEMISIL…
Thickening efficiency scales non-linearly with BET surface area. In a standard epoxy resin at 3 wt% loading, SEMISIL 150 delivers roughly 15–20 Pa·s, while SEMISIL 380 achieves 50–70 Pa·s under identical shear conditions. This 3–4× potency jump means formulators can reduce filler loading by 30–50% when stepping up from SEMISIL 150 to SEMISIL 380, cutting raw material volume while maintaining target rheology. However, higher-BET grades also increase thixotropic index (ratio of low-shear to high-shear viscosity), which benefits anti-sag coatings but can complicate spray atomization. Grade selection must balance viscosity target against application method.
| Grade | BET (m²/g) | Viscosity at 3 wt% in epoxy (Pa·s) | Relative loading to reach 30 Pa·s |
|---|---|---|---|
| SEMISIL 150 | 150 ± 15 | 15–20 | 4.5–5.0 wt% |
| SEMISIL 200 | 200 ± 25 | 25–35 | 3.0–3.5 wt% |
| SEMISIL 300 | 300 ± 30 | 40–55 | 2.0–2.5 wt% |
| SEMISIL 380 | 380 ± 30 | 50–70 | 1.5–2.0 wt% |
The table below summarizes key physical and chemical specifications across all four SEMISIL hydrophilic grades. All values represent typical production ranges under standard test conditions (ISO 9277 for BET, ISO 787-9 for pH, ISO 787-2 for moisture).
| Property | SEMISIL 150 | SEMISIL 200 | SEMISIL 300 | SEMISIL 380 |
|---|---|---|---|---|
| BET surface area (m²/g) | 150 ± 15 | 200 ± 25 | 300 ± 30 | 380 ± 30 |
| Primary particle size (nm) | ~12 | ~10 | ~8 | ~7 |
| Tamped density (g/L) | ~60 | ~50 | ~40 | ~35 |
| pH (4% dispersion) | 3.7–4.5 | 3.7–4.5 | 3.7–4.5 | 3.7–4.5 |
| Moisture content (%) | ≤ 1.0 | ≤ 0.8 | ≤ 0.8 | ≤ 0.8 |
| SiO₂ content (%) | ≥ 99.8 | ≥ 99.8 | ≥ 99.8 | ≥ 99.8 |
| Best-fit applications | Clear coats, LED encapsulants | General-purpose thickening | Adhesives, sealants | Anti-sag coatings, gel coats |
For most thickening applications, SEMISIL 200 offers the best balance of viscosity efficiency and optical clarity; step up to SEMISIL 300 or 380 only when maximum thixotropy or minimum loading is the priority, and down to SEMISIL 150 when transparency cannot be compromised.
SEMISIL 380 has 2.5× the BET surface area of SEMISIL 150 (380 vs 150 m²/g), giving it roughly 3–4× greater thickening potency per unit weight. This means formulators need 40–50% less SEMISIL 380 to reach the same viscosity target, but at the cost of higher haze in transparent systems.
SEMISIL 150 is best for clear coatings where optical clarity is critical. At 1–2 wt% loading it keeps haze below 2%, while higher-BET grades like SEMISIL 300 or 380 push haze above 3–6% at identical loading levels.
Higher BET surface area means more silanol groups per gram, which form denser hydrogen-bond networks in liquid media. Each step up the SEMISIL range (150→200→300→380) reduces the loading needed to reach a target viscosity by approximately 20–30%.
SEMISIL 380 costs 15–25% more per kilogram due to more demanding pyrogenic synthesis conditions. However, because it requires 40–50% less loading for equivalent thickening, the cost-per-unit-effect in a finished formulation is often 10–20% lower.
SEMISIL 300 can be used in UV-curable adhesives where slight haze is acceptable (3–5% at 1–2 wt%). For optically critical UV-cure applications like display bonding or LED encapsulation, SEMISIL 150 or 200 is preferred to maintain haze below 2%.
SEMISIL 200 typically provides effective anti-settling at 1.0–2.5 wt% loading, depending on particle density and resin viscosity. This creates a yield stress sufficient to suspend pigments and fillers up to 4–5 g/cm³ density without significant impact on application viscosity.
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