Silicone oil

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.[1]

Structure

Like all siloxanes (e.g., hexamethyldisiloxane), the polymer backbone consists of alternating silicon and oxygen 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 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[2] 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.

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. 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.

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.[3]

Automotive use

Silicone oil was commonly used as the fluid in the automobile cooling fan clutch assemblies, before the industry switched to electric cooling fans.[4]

References

  1. ↑ Moretto, Hans-Heinrich; Schulze, Manfred; Wagner, Gebhard (2005). "Silicones". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a24_057.
  2. ↑ Miyahara, H; Nakajima, A; Wada, J; Yanabu, S (June 2006), "Breakdown Characteristics of Combined Insulation in Silicone Oil for Electric Power Apparatus", Properties and applications of Dielectric Materials, 2006. 8th International Conference, 2006 IEEE 8th International Conference on Properties and applications of Dielectric Materials: 661–664, doi:10.1109/ICPADM.2006.284264, ISBN 1-4244-0190-9
  3. ↑ Martín-Gil, J; Martín-Gil, FJ; De Andrés Santos, AI; et al. (1997). "Thermal behaviour of medical grade silicone oils". J Anal Appl Pyrolysis. 42 (2): 151–158. doi:10.1016/S0165-2370(97)00002-8.
  4. ↑ Doremus, R. H. (2002). "Viscosity of silica". J. Appl. Phys. 92 (12): 7619–7629. Bibcode:2002JAP....92.7619D. doi:10.1063/1.1515132.
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