May. 13, 2024
Chemicals
A silicone oil is any liquid polymerized siloxane with organic side chains. The most important member is polydimethylsiloxane. These polymers are of commercial interest because of their relatively high thermal stability and their lubricating properties.
Like all siloxanes (e.g., hexamethyldisiloxane), the polymer backbone consists of alternating silicon and oxygen atoms (...Si−O−Si−O−Si...). Many groups can be attached to the tetravalent silicon centers, but the dominant substituent is methyl or sometimes phenyl. Many silicone liquids are linear polymers end-capped with trimethylsilyl groups, while others are cyclosiloxanes.
Silicone oils are primarily used as lubricants, thermic fluid oils, or hydraulic fluids. They are excellent electrical insulators and, unlike their carbon analogues, are non-flammable. Their temperature stability and good heat-transfer characteristics make them widely used in laboratories for heating baths ("oil baths") placed on top of hotplate stirrers, as well as in freeze-dryers as refrigerants. Silicone oil is also commonly used as the working fluid in dashpots, wet-type transformers, diffusion pumps, and in oil-filled heaters. Aerospace applications include the external coolant loop and radiators of the International Space Station Zvezda module, which rejects heat in the vacuum of space.
The class of silicone oils known as cyclosiloxanes has similar properties to other non-cyclic siloxane liquids but also features relatively high volatility, making it useful in various cosmetic products such as antiperspirants.
Some silicone oils, like simethicone, are potent anti-foaming agents due to their low surface tension. They are used in industrial applications such as distillation or fermentation, where excess foam can be problematic. They may also be added to cooking oils to prevent excessive foaming during deep frying. Silicone oils used as lubricants can inadvertently act as defoamers (contaminants) in processes where foam is desired, such as in the manufacture of polyurethane foam.
Silicone oil is also one of the two main ingredients in Silly Putty, along with boric acid.
Silicone oil can be used as a gun lubricant. It is compatible with the rubber, plastic, and metal parts frequently found in firearms. Due to the high surface adhesion of silicone oil, it forms a persistent film, which may be useful in protecting guns during extended storage.
Consumer products to control flatulence often contain silicone oil. Silicone oils have been used as a vitreous fluid substitute to treat difficult cases of retinal detachment, such as those complicated with proliferative vitreoretinopathy, large retinal tears, and penetrating ocular trauma. Additionally, silicone oil is used in general medicine and surgery. Because of silicone oil's water-repelling and lubricating properties, it is considered an appropriate material to maintain surgical instruments. It is also used in digital rectal examinations (DRE).
Silicone oil has been commonly used as the fluid in automobile cooling fan clutch assemblies and is still used in newer electronic fan clutches.
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