Dimethyl silicone oil, also known as methyl silicone oil, is a colorless, transparent, oily liquid with a wide range of commercial applications.
Domestically produced products are generally designated as 201, with the chemical formula MDnM, where M represents methyl (-CH3) and D represents a dimethylsiloxane unit.
Properties of Methyl Silicone Oil
Viscosity-Temperature Properties
The viscosity-temperature coefficient of methyl silicone oil is much lower than that of mineral oil, approximately 0.6, meaning its viscosity changes less with temperature.
Compressibility and Lubricity
Methyl silicone oil has high compressibility, but lower than that of mineral oil. Its compressibility decreases with increasing molecular weight. Methyl silicone oil has extremely high shear resistance, more than 20 times that of top-grade mineral oils, making it ideal for use as a lubricant. Although it is difficult to form a stable lubricating film on steel surfaces and is not suitable for heavy loads, it performs excellently in lubrication applications between plastic materials.
Temperature Resistance
Methyl silicone oil exhibits excellent high and low temperature resistance, allowing for long-term use within a wide temperature range of -40℃ to 200℃, a capability unmatched by most mineral oils. It shows almost no oxidation below 150℃, and even after heating at 200℃ for 16 hours, its viscosity increases by only 10%. The tendency for side-chain oxidative crosslinking in methyl silicone oil only becomes significant when the temperature exceeds 200℃.
Surface Activity
Due to its low surface tension, methyl silicone oil exhibits high surface activity and hydrophobicity, making it a highly effective defoamer and mold release agent.
Thermophysical Properties
Methyl silicone oil has a relatively low specific heat capacity, approximately one-third that of water. Its thermal expansion is greater than that of water and mercury, and similar to that of benzene. The thermal conductivity of methyl silicone oil ranges from 0.14 to 0.16 W/(m·K), approximately one-quarter that of water.
Electrical Insulation Properties: Methyl silicone oil is an excellent electrical insulating material with a volume resistivity exceeding 1 × 10^14 Ω·cm and an insulation strength exceeding 14 kV/mm. Its dielectric constant (ε) is between 2.64 and 2.75, and its dielectric loss tangent (tanδ) is less than 6 × 10^-4. These parameters exhibit minimal variation over a frequency range of 10^3–10^7 Hz and a temperature range of -40℃ to 150℃.
