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.

Structure

Like all siloxanes (e.g.,

hexamethyldisiloxane Hexamethyldisiloxane (HMDSO or MM) is an organosilicon compound with the formula O i(CH3)3. This volatile colourless liquid is used as a solvent and as a reagent in organic synthesis. It is prepared by the hydrolysis of trimethylsilyl chlori ...

), the polymer backbone consists of alternating silicon and

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

atoms (...Si−O−Si−O−Si...). Many groups can be attached to the tetravalent silicon centres, but the dominant substituent is methyl or sometimes phenyl. Many silicone liquids are linear polymers end-capped with

trimethylsilyl group A trimethylsilyl group (abbreviated TMS) is a functional group in organic chemistry. This group consists of three methyl groups bonded to a silicon atom minus;Si(CH3)3 which is in turn bonded to the rest of a molecule. This structural group i ...

s. Other silicone liquids are cyclosiloxanes.

Applications

Silicone oils are primarily used as

lubricant A lubricant (sometimes shortened to lube) is a substance that helps to reduce friction between surfaces in mutual contact, which ultimately reduces the heat generated when the surfaces move. It may also have the function of transmitting forces, ...

s, 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 science, scientific or technological research, experiments, and measurement may be performed. Laboratories are found in a variety of settings such as s ...

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 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 Simeticone (International Nonproprietary Name, INN), also known as simethicone (United States Adopted Name, USAN), is an anti-foaming agent used to reduce bloating, discomfort or pain caused by excessive gas. Medical uses Simeticone is used to ...

, 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 (physics), tension is what allows objects with a higher density than water such as razor blades and insects (e.g. Ge ...

. They are used in industrial applications such as distillation or

fermentation Fermentation is a type of anaerobic metabolism which harnesses the redox potential of the reactants to make adenosine triphosphate (ATP) and organic end products. Organic molecules, such as glucose or other sugars, are catabolized and reduce ...

, 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 Cooking oil, oil, as opposed to the shallow frying used in conventional frying done in a fryi ...

. Silicone oils used as lubricants can be inadvertent defoamers (contaminants) in processes where foam is desired, such as in the manufacture of

polyurethane Polyurethane (; often abbreviated PUR and PU) is a class of polymers composed of organic chemistry, organic units joined by carbamate (urethane) links. In contrast to other common polymers such as polyethylene and polystyrene, polyurethane term ...

foam. Silicone oil is also one of the two main ingredients in Silly Putty, along with boric acid. Silicone oil serves as an effective gun lubricant, suitable for use with the rubber, plastic, and metal components commonly found in firearms. Its high surface adhesion allows it to create a long-lasting protective film, which is beneficial for preserving guns during prolonged storage.

Medical uses

Consumer products to control

flatulence Flatulence is the expulsion of gas from the Gastrointestinal tract, intestines via the anus, commonly referred to as farting. "Flatus" is the medical word for gas generated in the stomach or bowels. A proportion of intestinal gas may be swal ...

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 Viscous Fan Coupling assemblies, and is still being used in the newer electronic fan assemblies.

References

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