Asilicone oil is any liquid polymerizedsiloxane with organic side chains. The most important member ispolydimethylsiloxane. These polymers are of commercial interest because of their relatively high thermal stability and their lubricating properties.[1]
Like all siloxanes (e.g.,hexamethyldisiloxane), the polymer backbone consists of alternating silicon andoxygen atoms (...Si−O−Si−O−Si...).[citation needed] Many groups can be attached to thetetravalent silicon centres, but the dominant substituent ismethyl or sometimesphenyl. Many silicone liquids are linear polymers end-capped withtrimethylsilyl groups. Other silicone liquids arecyclosiloxanes.[citation needed]
Silicone oils are primarily used aslubricants, thermic fluid oils orhydraulic fluids. They are excellentelectrical insulators[2] and, unlike their carbon analogues, are non-flammable. Their temperature stability and good heat-transfer characteristics make them widely used inlaboratories for heating baths ("oil baths") placed on top ofhotplate stirrers, as well as infreeze-dryers asrefrigerants.[citation needed] Silicone oil is also commonly used as the working fluid indashpots, wet-typetransformers,diffusion pumps and inoil-filled heaters. Aerospace use includes the external coolant loop and radiators of the International Space StationZvezda module, which rejects heat in the vacuum of space.[3]
The class of silicone oils known as cyclosiloxanes has many of the same properties as other non-cyclicsiloxane liquids but also has a relatively highvolatility, making it useful in a number of cosmetic products such as antiperspirant.
Some silicone oils, such assimethicone, are potentanti-foaming agents due to their lowsurface tension. They are used in industrial applications such asdistillation orfermentation, where excessive amounts offoam can be problematic. They are sometimes added tocooking oils to prevent excessive foaming duringdeep frying. Silicone oils used as lubricants can be inadvertent defoamers (contaminants) in processes where foam is desired, such as in the manufacture ofpolyurethane foam.
Silicone oil is also one of the two main ingredients inSilly Putty, along withboric acid.
Consumer products to controlflatulence often contain silicone oil.[4] Silicone oils have been used as avitreous fluid substitute to treat difficult cases of retinal detachment, such as those complicated withproliferative vitreoretinopathy, large retinal tears, and penetrating ocular trauma.[5] Additionally, silicone oil is used in general medicine and surgery. Because of silicone oil's water repellent and lubricating properties, it is considered an appropriate material to maintain surgical instruments. They are also used in digital rectal examinations (DRE).
Silicone oil has been commonly used as the fluid in the automobile Viscous Fan Coupling assemblies, and is still being used in the newer electronic fan assemblies.[6]