Definition and Chemical Nature of Silicone Oil
Silicone oil, chemically known as polydimethylsiloxane (PDMS), is a linear polysiloxane compound with a backbone composed of alternating silicon and oxygen atoms, flanked by methyl (CH₃) groups. Its molecular structure endows silicone oil with unique physical and chemical properties: the Si-O bond energy in the backbone reaches as high as 460 kJ/mol, far exceeding the C-C bond energy of the carbon chain (347 kJ/mol), resulting in excellent thermal stability and chemical inertness. This structural characteristic ensures silicone oil's stability over a wide temperature range of -50°C to 200°C and its strong resistance to corrosive substances such as acids, alkalis, and salts.

Physical Properties and Performance Advantages of Silicone Oil
Silicone oil is a colorless, transparent or pale yellow, odorless, and non-toxic oily liquid with a density of approximately 0.963 g/cm³ and a surface tension as low as 21 mN/m (only one-third that of water). Its core performance advantages include:
Thermal Stability: Its flash point exceeds 300°C and it can withstand long-term use at 200°C without decomposition, far exceeding the 150°C limit of mineral oil.
Electrical Insulation: Its volume resistivity reaches 1×10¹⁵ Ω·cm and its dielectric loss tangent is less than 0.001, making it an ideal replacement for transformer oil and capacitor oil.
Lubrication: Its viscosity-temperature coefficient is only 0.0006/°C, and its viscosity changes minimally from -50°C to 200°C, making it suitable for mechanical lubrication in extreme temperature environments.
Surface Activity: Its low surface tension provides excellent defoaming, mold release, and water-repellent properties, reducing raw material consumption by over 10% in the coatings and printing and dyeing industries.

Diverse Applications of Silicone Oil
Industrial Applications: It is used as a high-temperature hydraulic fluid in aviation hydraulic systems. As an insulating oil for transformer filling, it can reduce volume by 30% and improve energy efficiency. As a damping fluid in precision instruments, its compression resistance is three times that of traditional hydraulic oils. Daily chemical industry: Modified silicone oils (such as polyether silicone oils), core ingredients in shampoos and skincare products, can reduce surface tension to below 25 mN/m, improve hair smoothness by 40%, and double the skin's moisturizing effect.
Medical field: Hydroxyl silicone oils, after being sterilized with ethylene oxide, can be used as defoaming agents in artificial heart-lung machines. Their biocompatibility complies with ISO 10993 standards and is non-cytotoxic.
Emerging technologies: Methyl vinyl silicone oils, used as photocurable resin bases in 3D printing, cure five times faster than traditional acrylates. Hydrogenated silicone oils can be used to create self-healing coatings through Si-H bond addition reactions.
Technological breakthroughs in modified silicone oils

By introducing functional groups such as phenyl and fluorine, silicone oil properties are optimized:
Methylphenyl silicone oil: With a phenyl content of 20%, the upper operating temperature limit is increased to 250°C, making it suitable for lubricating bearings in nuclear power plant main pumps. Fluorosilicone oil: After replacing the methyl group with a trifluoropropyl group, solvent resistance increases tenfold, allowing long-term immersion in organic solvents such as gasoline and acetone.
Aminosilicone oil: After introducing an amino group into the terminal group, adsorption capacity on cellulose fibers increases threefold, making it a core ingredient in cotton fabric softeners.
This innovation in materials science has enabled silicone oil to expand from a traditional industrial lubricant into high-end fields such as biomedicine, new energy, and semiconductors, making it an indispensable "liquid engineer" in modern industry.