Perfluorocarbon

  Perfluorocarbons (PFCs) are compounds derived from hydrocarbons by replacement of hydrogen atoms by fluorine atoms. PFCs are made up of atoms of carbon, fluorine, and/or sulfur.

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Medicine

Perfluorocarbons are commonly used in eye surgery as temporary replacements of the vitreous humor in retinal detachment surgery. The length of the perfluorated carbon chain determines the physical properties of a particular perfluorocarbon. Small chain perfluorocarbons, such as perfluoro-propane, are gases that rise inside the eye and seal retinal holes. Larger chain perfluorocarbons, such as perfluoro-octane, are liquids heavier than water and are used in surgery to immobilize an infolded retina.

Perfluorocarbons are also used in contrast-enhanced ultrasound to improve ultrasound signal backscatter. The perfluorocarbons used in the microbubbles of some ultrasound contrast media are liquids at room temperature, but gases at body temperature. The gas-filled microbubbles oscillate and vibrate when a sonic energy field is applied and characteristically reflect ultrasound waves. This distinguishes the microbubbles from surrounding tissues.

Their stability, inertness, low diffusion rate and solubility increase the duration of contrast enhancement as compared to microbubbles containing air. The uses of PFCs in artificial blood and liquid breathing are currently being investigated. The theory behind liquid breathing is that, since perfluorocarbons carry oxygen so well, a person should be able to breathe normally with lungs filled with perfluorocarbon fluids. However, in practice liquid breathing has so far proved to be problematic; trials on animals have shown evidence of lung damage and carbon dioxide build-up from respiration. In addition, as perfluorocarbon liquids (and liquids in general) are much denser and more viscous than air, rates of breathing, and therefore of gas exchange, are limited.

Industry and the environment

PFCs are being used in refrigerating units and "clean" fire extinguishers. However, PFCs are extremely potent greenhouse gases, and they are a long-term problem with a lifetime up to 50,000 years (PMID 14572085). In a 2003 study, the most abundant atmospheric PFC was tetrafluoromethane (PMID 14572085). The greenhouse warming potential (GWP) of tetrafluoromethane is 6,500 times that of carbon dioxide, and the GWP of hexafluoroethane is 9,200 times that of carbon dioxide.[1] Several governments concerned about the properties of PFCs have already tried to implement international agreements to limit their usage before it becomes a global warming issue. PFCs are one of the classes of compounds regulated in the Kyoto Protocol. Larger PFC compounds include PFOS and PFOA, which are persistent in the environment and are detected in blood samples all over the world.

See also

• Fluorinert - Coolants manufactured by 3M, some of which may contain PFCs
• Fluoropolymer
• Liquid breathing