N-1180-50 is a dispersion of hollow nanosilica particles specifically designed to achieve an ultra‑low refractive index while maintaining high optical transparency. With a unique hollow interior structure, it offers a refractive index as low as 1.18 - significantly lower than conventional solid silica (≈1.46). This makes N-1180-50 a practical additive for low‑index coatings, anti‑reflective (AR) films, fiber optic claddings, and optical display materials.
The product is supplied as a semi‑transparent liquid in propylene glycol monomethyl ether (PGME), a solvent commonly used in UV‑curable coating formulations. Its particle size is controlled between 40 and 50 nm, which is well below the visible light wavelength, thereby minimizing light scattering and preserving transparency.
Key Technical Specifications
| Parameter | Value |
|---|---|
| Appearance | Semi‑transparent liquid |
| Nanosilica content (wt%) | 50 |
| Viscosity at 25°C (mPa·s) | 50 – 150 |
| Solvent (PGME) content (wt%) | 45 – 50 |
| Refractive index (nD25) | 1.18 |
| Relative density | 0.85 – 0.95 |
| Nanoparticle size | 40 – 50 nm |
Performance Characteristics
1. Ultra‑Low Refractive Index (1.18)
The hollow morphology creates an internal air cavity (refractive index ≈1.0), effectively lowering the overall refractive index of the particles. When combined with low‑index binder resins (e.g., fluorinated or silicone acrylates), N-1180-50 enables coating refractive indices in the range of 1.20 – 1.30, which is essential for multilayer AR stack designs.
2. High Optical Transparency (>95%)
At 40–50 nm, the nanoparticles are much smaller than the shortest visible wavelength (380 nm). As a result, they do not scatter light significantly. Coatings formulated with N-1180-50 exhibit haze levels below 0.5% and total light transmittance above 95%, provided the dispersion is well‑matched with the resin system.
3. High Solid Content with Moderate Viscosity
A nanosilica content of 50 wt% combined with a viscosity of only 50–150 mPa·s indicates excellent particle stabilization and deagglomeration. This allows formulators to either use the product directly or dilute it without sacrificing coating uniformity. High solids also enable thicker wet films and reduce drying shrinkage.
4. PGME Solvent Compatibility
PGME (propylene glycol monomethyl ether) is a widely used solvent in UV coatings, photoresists, and optical films. It has a moderate evaporation rate (boiling point ≈120°C) and good solubility for most acrylate and epoxy resins. This solvent choice makes N-1180-50 readily compatible with existing UV‑curable coating lines.
Primary Applications
Anti‑Reflective (AR) Coatings
By applying a layer containing N-1180-50 on top of a high‑refractive‑index layer (e.g., n ≈1.65–1.70), destructive interference can reduce surface reflection to below 0.5%. This is used in:
Smartphone and tablet displays
Television screens
Anti‑reflective films for architectural glass
Photovoltaic glass (to increase light transmission)
Optical Fiber Claddings
The refractive index of the fiber cladding must be lower than that of the core. N-1180-50's n=1.18 makes it suitable for polymer claddings in plastic optical fibers (POFs) or for coating silica fibers where a low‑index buffer layer is needed to guide light efficiently.
Low‑Index Adhesives and Gap Fillers
In lens modules, optical sensors, or waveguide devices, refractive index matching or contrast is critical. N-1180-50 can be blended with UV‑curable resins to produce low‑index adhesives (n=1.20–1.25) for bonding optical components without increasing reflection losses.
Nano‑Coating Additive for Optical Films
As an additive, N-1180-50 reduces the overall refractive index of polymer coatings without compromising clarity. It is particularly useful for:
Anti‑glare (AG) films with controlled haze
Hard coatings requiring both low index and abrasion resistance
Encapsulation layers for OLED or micro‑LED displays
Processing Guidelines
Compatibility Testing
Because the hollow silica surface is polar (silanol groups), compatibility with non‑polar or highly hydrophobic resins may be limited. Always conduct a small‑scale mix test: add N-1180-50 to the resin solution and check for:
Appearance: A clear or slightly bluish mixture indicates good dispersion. Milky or sediment‑forming mixtures signal incompatibility.
Coating haze: Apply a thin film and measure haze. Values >1% suggest agglomeration.
Drying and Curing Conditions
The hollow structure can collapse if the solvent is driven off too rapidly. To preserve the low‑index property:
Use a two‑stage drying process: 60–70°C for 1–2 minutes (gentle solvent evaporation), then cure at higher temperature or UV.
Avoid direct IR heating or high‑velocity air knives immediately after coating.
UV Formulation Tips
Combine with low‑index oligomers (e.g., fluorinated polyurethane acrylates, RI ≈1.30–1.35) to maximize the refractive index drop.
Typical loading: 30–60 wt% of N-1180-50 (as received) on total solid content.
Add photoinitiators soluble in PGME (e.g., Irgacure 184, TPO-L) at 1–3% relative to total resin solids.
Comparison with Conventional Silica Sols
| Feature | N-1180-50 (Hollow) | Standard Solid Silica Sol |
|---|---|---|
| Refractive index | 1.18 | 1.46 |
| Particle morphology | Hollow (air‑filled) | Solid |
| Transparency in coating | Excellent (>95%) | Good (>92%) |
| Lowest achievable RI in composite | 1.20 | ~1.38 (needs very low resin RI) |
| Typical solvent | PGME | Water or isopropanol |
Storage and Handling
Store in tightly sealed containers at 5–35°C away from direct sunlight.
Avoid freezing; the dispersion may destabilize below 0°C.
Shelf life: 12 months from date of manufacture when stored properly.
Agitate gently before use – do not use high‑shear mixing which could break hollow particles.
Limitations
Not recommended for purely aqueous systems (PGME is not fully water‑miscible beyond ~20%).
Mechanical strength of pure hollow silica coatings is lower than solid silica; use with a sufficient binder matrix for abrasion resistance.
The low refractive index is achieved only when the hollow structure remains intact. Excessive temperature (>200°C) or extreme pressure may cause collapse.
Conclusion
N-1180-50 offers a balanced combination of an ultra‑low refractive index (1.18), high transparency, and practical formulation convenience via PGME solvent. Its 40–50 nm particle size and 50% solid content make it a versatile building block for anti‑reflective coatings, optical fiber claddings, low‑index adhesives, and advanced display films. Proper compatibility testing and controlled drying are the keys to unlocking its full performance.
For formulators seeking a ready‑to‑use hollow silica dispersion with reproducible optical properties, N-1180-50 provides a reliable, scalable solution.