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, lubricating, and

dielectric In electromagnetism, a dielectric (or dielectric medium) is an electrical insulator that can be polarised by an applied electric field. When a dielectric material is placed in an electric field, electric charges do not flow through the ma ...

properties.

Structure

Like all siloxanes (e.g., hexamethyldisiloxane), the polymer backbone consists of alternating silicon and

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...

atoms (...Si−O−Si−O−Si...). Many groups can be attached to the tetravalent silicon centres, but the dominant substituent is

methyl In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula . In formulas, the group is often abbreviated as Me. This hydrocarbon group occurs in ...

or sometimes phenyl. Many silicone liquids are linear polymers end-capped with trimethylsilyl groups. Other silicone liquids are cyclosiloxanes.

Applications

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 A laboratory (; ; colloquially lab) is a facility that provides controlled conditions in which scientific or technological research, experiments, and measurement may be performed. Laboratory services are provided in a variety of settings: physi ...

for heating baths ("oil baths") placed on top of hotplate stirrers, as well as in freeze-dryers as

refrigerant A refrigerant is a working fluid used in the refrigeration cycle of air conditioning systems and heat pumps where in most cases they undergo a repeated phase transition from a liquid to a gas and back again. Refrigerants are heavily regulated ...

s. Silicone oil is also commonly used as the working fluid in dashpots, wet-type

transformer A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer' ...

diffusion pump Diffusion pumps use a high speed jet of vapor to direct gas molecules in the pump throat down into the bottom of the pump and out the exhaust. They were the first type of high vacuum pumps operating in the regime of free molecular flow, where the ...

s and in oil-filled heaters. Aerospace use includes 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 many of the same properties as other non-cyclic siloxane liquids but also has a relatively high volatility, making it useful in a number of cosmetic products such as antiperspirant. Some silicone oils, such as simethicone, are potent anti-foaming agents due to their low

surface tension Surface tension is the tendency of liquid surfaces at rest to shrink into the minimum surface area possible. Surface tension is what allows objects with a higher density than water such as razor blades and insects (e.g. water striders) t ...

. They are used in industrial applications such as

distillation Distillation, or classical distillation, is the process of separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distillation is the he ...

or fermentation, where excessive amounts of foam can be problematic. They are sometimes added to cooking oils to prevent excessive foaming during

deep frying Deep frying (also referred to as deep fat frying) is a cooking method in which food is submerged in hot fat, traditionally lard but today most commonly oil, as opposed to the shallow oil used in conventional frying done in a frying pan. ...

. Silicone oils used as lubricants can be inadvertent 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.

Medical uses

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 repellent and lubricating properties, it is considered an appropriate material to maintain surgical instruments. They are also used in digital rectal examinations (DRE).

Automotive use

Silicone oil has been commonly used as the fluid in the automobile cooling fan clutch assemblies, and is still being used in the newer electronic fan clutches.

References

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