A silicone oil is any liquid polymerized siloxane with organic side chains. They are formed with a backbone of alternating silicon-oxygen atoms (...Si-O-Si-O-Si...) – i.e. siloxane – rather than carbon atoms (...C-C-C-C...). Other species attach to the tetravalent silicon atoms, not to the divalent oxygen atoms which are fully committed to forming the siloxane chain. A typical example is Hexamethyldisiloxane, where three methyl groups attach to each silicon atom to form Si(CH3)3OSi(CH3)3. The carbon analogue would be an alkylalkane, that is 2,2,4,4-tetramethylpentane C(CH3)3CH2C(CH3)3.
See also Polydimethylsiloxane.
Silicone oils are primarily used as lubricants 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.
Some silicone oils, such as simethicone, are potent anti-foaming agents due to their low surface tension. They are used in industrial applications such as distillation or fermentation where excessive amounts of foam can be problematic. They are sometimes added to cooking oils to prevent excessive frothing during deep frying. Silicone oils used as lubricants can be inadvertent defoamers (contaminants) in processes where foam is desired, such as in the manufacture of polyurethane foam.
Consumer products to control flatus (antiflatulents) 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, giant retinal tears, and penetrating ocular trauma.
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