2025-12-31
Dimethyl Silicone Oil (PDMS) Properties & CAS Comparison
A Systematic Engineering & Application-Oriented Analysis of Different CAS Numbers and Specifications
Dimethyl Silicone Oil, also known as Polydimethylsiloxane (PDMS), is a key functional fluid in the organosilicon industry. Its chemical inertness, high thermal stability, low surface tension, excellent electrical insulation, and broad viscosity range make it essential across industrial lubrication, defoaming, mold release, electronics, thermal management, personal care, cosmetic, and medical applications.
Silico® provides high-quality, application-optimized PDMS solutions designed for consistent performance in industrial use.
PDMS is commonly listed under multiple CAS numbers (63148-62-9, 9016-00-6, 9006-65-9), which can cause confusion in procurement, technical specifications, and formulation. This article clarifies these CAS numbers, physical properties, viscosity grades, and application selection guidance to support accurate technical decision-making.
Table of Contents
- 1. What Is Dimethyl Silicone Oil (PDMS)?
- 2. Fundamental Differences Between Common CAS Numbers for Dimethyl Silicone Oil
- 3. Core Physical and Chemical Properties of Dimethyl Silicone Oil
- 4. Systematic Comparison of Viscosity Grades and Specifications (25 °C)
- 5. How Physical Property Differences Influence Real-World Performance
- 6. Practical Selection Logic for Engineering and Formulation Applications
- 7. How to Choose the Right Dimethyl Silicone Oil
- 8. Conclusion
1. What Is Dimethyl Silicone Oil (PDMS)?
Understanding Performance from Molecular Structure
Dimethyl silicone oil is essentially a linear polysiloxane fluid composed of repeating –Si(CH₃)₂–O– units. Its backbone consists of silicon–oxygen (Si–O–Si) bonds, which exhibit significantly higher bond energy and greater molecular flexibility compared to conventional carbon-chain polymers.
This unique molecular structure is the fundamental reason why PDMS maintains stable physical properties over a wide temperature range.
At room temperature, dimethyl silicone oil is typically a colorless, transparent, odorless, non-polar liquid. It is insoluble in water but compatible with many organic solvents.
The typical service temperature range spans from –50 °C to 200 °C, and certain high-grade products can operate beyond this range under inert conditions.
2. Fundamental Differences Between Common CAS Numbers for Dimethyl Silicone Oil
In commercial and technical documentation, the following three CAS numbers are most frequently encountered:
1️⃣ CAS 63148-62-9 — Polydimethylsiloxane (Mainstream International Standard)
This is the most widely accepted and internationally recognized CAS number for PDMS today. It is commonly used in export customs declarations, MSDS, TDS, and global chemical databases.
Most modern industrial-grade, electronic-grade, and standard PDMS products are registered under this CAS number.
Most modern industrial-grade, electronic-grade, and standard PDMS products are registered under this CAS number.
2️⃣ CAS 9016-00-6 — Dimethylpolysiloxane (Historical Registration)
This CAS number appears mainly in earlier industrial literature, legacy databases, and traditional industry standards.
Although less frequently used in new projects, it refers to the same linear PDMS chemical entity as CAS 63148-62-9.
3️⃣ CAS 9006-65-9 — Dimethyl Silicone Oil (Application-Oriented Naming)
This CAS number is commonly found in lubricant, defoamer, and mold release agent documentation, emphasizing the functional identity of “silicone oil” rather than strict polymer nomenclature.
Professional Conclusion
From the perspective of chemical structure, molecular composition, and core physical properties, these three CAS numbers do not represent different substances.
They refer to the same linear dimethylsiloxane fluid, with differences arising from registration systems, historical context, or application-driven naming conventions.
They refer to the same linear dimethylsiloxane fluid, with differences arising from registration systems, historical context, or application-driven naming conventions.
Understanding this distinction is critical for avoiding misunderstandings in cross-border procurement, regulatory compliance, and technical communication.
3. Core Physical and Chemical Properties of Dimethyl Silicone Oil
An Engineering Perspective
The versatility of dimethyl silicone oil across multiple industries stems from a highly synergistic set of physical properties:
- High chemical stability: Resistant to most acids, alkalis, and oxidative environments
- Excellent thermal stability: Minimal degradation or crosslinking under long-term heat exposure
- Low surface tension: Significantly lower than water and mineral oils, enabling superior wetting and spreading
- Outstanding lubricity and film-forming ability: Stable lubrication on metal, plastic, and rubber surfaces
- Superior electrical insulation: Ideal as a dielectric fluid and moisture barrier
- Controllable physiological inertness: High-purity grades suitable for personal care and specialty applications
4. Systematic Comparison of Viscosity Grades and Specifications (25 °C)
Among all physical parameters, kinematic viscosity is the most critical factor differentiating dimethyl silicone oil grades, as it directly correlates with molecular weight.
| Viscosity Range (cSt) | Relative Density (25 °C) | Flash Point (°C) | Typical Applications |
|---|---|---|---|
| 5–20 | 0.90–0.95 | ≥80–200 | Defoamers, personal care formulations, precision lubrication |
| 50–100 | 0.95–0.97 | ≥250–310 | General-purpose silicone oil, light-load lubrication |
| 350–500 | 0.96–0.97 | ≥290–315 | Industrial lubrication, mold release agents |
| 1,000–5,000 | 0.96–0.97 | ≥290–315 | Industrial lubrication, mold release agents |
| 10,000–30,000 | ≈0.97 | >300 | Heavy-load lubrication, sealing media |
| >100,000 | ≈0.97 | >300 | Damping fluids, buffering and vibration control systems |
5. How Physical Property Differences Influence Real-World Performance
Relationship Between Viscosity, Lubrication, and Defoaming Efficiency
Low-viscosity PDMS: Excellent flowability and rapid surface spreading; ideal for defoaming, surface treatment, and cosmetic formulations
Medium-viscosity PDMS: Balanced performance; the most widely used grade in industrial applications
High-viscosity PDMS: Thick, stable films with strong load-bearing capacity; suitable for damping, cushioning, and high-temperature environments
Environmental Adaptability and Long-Term Stability
Due to the robust siloxane backbone, dimethyl silicone oil maintains consistent performance under high temperature, humidity, electrical fields, and mechanical shear, making it a preferred choice for dielectric fluids and thermal management systems.
At this performance level, Silico® PDMS products are engineered to ensure viscosity stability and batch-to-batch consistency across demanding industrial environments.
6. Practical Selection Logic for Engineering and Formulation Applications
When selecting dimethyl silicone oil for a specific application, a systematic evaluation should consider:
- Operating temperature and load conditions: Define viscosity boundaries
- Primary functional requirement: Lubrication, defoaming, isolation, or damping
- Purity and regulatory compliance: Especially for electronics, cosmetics, or specialty formulations
CAS number alignment: Ensure consistency between procurement documents and technical specifications
7. How to Choose the Right Dimethyl Silicone Oil
When specifying dimethyl silicone oil, professional buyers should focus on:
- Viscosity tolerance
- Molecular weight distribution
- Volatile content
- Thermal performance range
- Compliance with REACH, RoHS, or other regulations
- Consistency across production batches
This approach ensures optimal performance across industrial, chemical, and formulation-based applications.
Silico® provides a full viscosity range of dimethyl silicone oils with stable molecular architecture and export-ready documentation to meet diverse global requirements.
8. Conclusion
The three commonly used CAS numbers—63148-62-9, 9016-00-6, and 9006-65-9—all refer to dimethyl silicone oil based on linear PDMS chemistry. Their differences lie mainly in historical usage, regulatory habits, and application-oriented naming, rather than in fundamental physical or chemical properties.
For engineers, formulators, and procurement specialists, viscosity grade, purity, and application fit should always take priority over CAS nomenclature.
Silico® remains committed to supplying reliable, high-performance dimethyl silicone oils designed for industrial lubrication, release, defoaming, and advanced material applications worldwide.
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