Phenyl Silicone Oil (Methyl Phenyl Silicone Fluid): High-Temperature Heat Transfer Fluid and High-Refractive-Index Optical Silicone
SEMITECH phenyl silicone oil is methyl-phenyl-modified PDMS — 5–50% phenyl substitution provides higher thermal stability (260–290°C vs 200°C), higher refractive index (1.51–1.58 vs 1.40), and lower freezing point (−65°C+) compared with pure methyl silicone. Multiple grades for heat transfer, optical, and aerospace lubricant applications.
Contents
| 5–50% | 260°C | 1.51–1.58 |
|---|---|---|
| Phenyl content range | Continuous service | Refractive index range |
Chemistry & Specifications
Methyl phenyl polysiloxane; clear pale-yellow to amber liquid; phenyl content drives thermal/optical/freezing properties.
Phenyl substitution provides three key modifications: (1) higher thermal stability via stronger phenyl-Si bonds; (2) higher RI from phenyl polarisability; (3) lower freezing point by disrupting methyl PDMS crystallisation.
SEMITECH stocks three tiers: Light (5–10% phenyl, RI 1.45, 250°C); Medium (15–25%, RI 1.49, 260°C); Heavy (40–50%, RI 1.55, 290°C). Multiple viscosity grades 50–1,000 cP per tier. CoA includes phenyl content (NMR/FT-IR, ±2%), viscosity, RI, water ≤300 ppm.
Applications: Heat Transfer Fluid, High-RI Optical, Aerospace Lubricant
High-temp heat transfer (250–290°C), LED encapsulant high-RI fluid, aerospace lubricant low-T grease, optical coupling fluid.
High-temperature heat transfer fluid is the largest application — solar thermal collectors, industrial process heating, and lab circulating baths. Provides 50–80°C higher service temperature than mineral oil with low-temperature flow to −65°C and flash point 280–320°C.
High-RI optical fluid at 25–50% phenyl for LED encapsulation, laser coupling, and microscopy immersion oil. Aerospace lubricant base oil at 5–15% phenyl for −65°C+ freeze-point depression. High-temperature dielectric fluid for transformer cooling at 200–250°C.
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Phenyl Content vs Application Property — Selection Guide
Light phenyl for heat transfer; medium for general optical; heavy for high-RI optical and high-T applications.
- Light (5–10% phenyl, RI 1.45) — heat transfer 250°C max; aerospace lubricant −65°C+; lowest cost premium (~25–35% over methyl silicone)
- Medium (15–25% phenyl, RI 1.49) — general-purpose heat transfer to 260°C; medium-RI optical; cost premium 50–70%
- Heavy (40–50% phenyl, RI 1.55) — high-RI optical (LED, laser, microscopy); heat transfer to 290°C; cost premium 100–150%
Procurement, Storage and Quality Control
CoA per shipment with phenyl content + RI verification; 200 kg drum / 1 t IBC; 24-month shelf life.
Standard packing 200 kg drums; 1 t IBC for high-volume heat transfer customers; 25 kg jerrycans for lab. MOQ 200 kg per grade. Lead time 2–4 weeks to Asia for Light/Medium, 4–6 weeks for Heavy and Europe/North America. Non-flammable (flash point 280–320°C); no N₂ blanket required. REACH-registered.
Phenyl Silicone Oil Specification Sheet — Three Phenyl-Content Tiers
SEMITECH stocked grades; CoA per batch with phenyl content + RI verification.
| Property | Light (5–10%) | Medium (15–25%) | Heavy (40–50%) |
|---|---|---|---|
| Phenyl content | 5–10% | 15–25% | 40–50% |
| Refractive index (25°C) | 1.43–1.46 | 1.47–1.50 | 1.53–1.58 |
| Density (25°C) | 0.99–1.01 g/cm³ | 1.02–1.06 g/cm³ | 1.10–1.14 g/cm³ |
| Continuous service temperature | ≤250°C | ≤260°C | ≤290°C |
| Pour point | −65°C | −55°C | −35°C |
| Flash point (closed cup) | 280–300°C | 290–315°C | 300–320°C |
| Viscosity range | 50–500 cP | 100–1,000 cP | 500–5,000 cP |
| Water content | ≤300 ppm | ≤300 ppm | ≤300 ppm |
| APHA colour | ≤30 | ≤50 | ≤100 |
| Cost premium vs methyl silicone | 25–35% | 50–70% | 100–150% |
| Primary application | Heat transfer, aerospace | General high-T, optical | High-RI optical, highest-T |
| Packaging | 200 kg drum / 1 t IBC | 200 kg drum / 1 t IBC | 200 kg drum / 25 kg pail |
| Shelf life | 24 months sealed | 24 months sealed | 24 months sealed |
FAQ
+How does phenyl silicone heat transfer fluid compare to Therminol VP-1 or Dowtherm?
Phenyl silicone offers lower fire risk (flash point 280–320°C vs ~120°C for biphenyl/DPO eutectics), wider operating range (−65°C to 290°C vs 12°C to 400°C for VP-1), better thermal cycling tolerance, but at 30–50% higher cost per kg. VP-1/Dowtherm is the right choice only when operating above 290°C.
+Why does my LED encapsulant develop yellowing during long-term operation at 120°C?
Typically caused by oxidation of organic contaminants or substrate residues, not the phenyl silicone itself. Confirm by replacing encapsulant with fresh material, check for organic contamination, and verify full cure before high-temperature service.
+Can I formulate a high-RI optical adhesive using phenyl silicone oil?
Phenyl silicone oil alone is a fluid. Formulate with a curable system: Pt-cured vinyl-phenyl-PDMS + PMHS, UV-cure with acrylate-modified phenyl-PDMS, or condensation cure with OH-terminated phenyl-PDMS + alkoxysilane crosslinker.