Silicone oil

Silicone oils (polymerized siloxanes) are silicon analogues of carbon based organic compounds, and can form (relatively) long and complex molecules based on silicon rather than carbon. Chains are formed of alternating silicon-oxygen atoms (...Si-O-Si-O-Si...) or 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 polydimethylsiloxane, where two methyl groups attach to each silicon atom to form (H₃C)[SiO(CH₃)₂]_nSi(CH₃). The carbon analogue would be an alkane, e.g. dimethylpropane C₅H₁₂ or (H₃C)[C(CH₃)₂](CH₃).

Silicone oils could be a basis for silicon-based organic life, but their more prosaic, primary uses are 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. Silicone oil is also commonly used as the working fluid in diffusion pumps.

Some silicone oils such as simethicone are potent anti-foaming agents. 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. Consumer products to control flatus (antiflatulents) often contain silicone oil. 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 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 . Silicone oil is also one of the two main ingredients in Silly Putty, along with boric acid. Silicone oil plays a useful role in gas powered airsoft guns where it is used to lubricate the rubber gas seals in gas blowback guns without degrading them as carbon-based oils would, as well as lubricating the moving parts of the guns.