Anti-fog agents, also known as anti-fogging agents and treatments, are chemicals that prevent the condensation of water in the form of small droplets on a surface which resemble fog. Anti-fog treatments were first developed by NASA during Project Gemini, and are now often used on transparent glass or plastic surfaces used in optical applications, such as the lenses and mirrors found in glasses, goggles, camera lenses, and binoculars. The treatments work by minimizing surface tension, resulting in a non-scattering film of water instead of single droplets. This works by altering the degree of wetting. Anti-fog treatments usually work either by application of a surfactant film, or by creating a hydrophilic surface.
Anti-fog agents were initially developed by NASA during the Project Gemini, for use on helmet visors. During Gemini 9A, in June 1966, Astronaut Eugene A. Cernan tested NASA's first space suit, and discovered during the space walk that his helmet visor fogged, among other issues. Cernan's suit was tested using the Spacecraft 9 life support system after the flight, when it was discovered that a small patch of the visor treated with an anti-fog solution remained clear of condensation. Later Gemini flights all included the anti-fog solution, for application prior to the space walk occurring.
Anti-fog agents are usually available as spray solutions, creams and gels, and wet wipes, while more resistant coatings are often applied during complex manufacturing processes. Anti-fog additives can also be added to plastics where they exude from the inside to the surface.
The following substances are used as anti-fog agents:
- Surfactants that minimize the surface tension of the water:
- Hydrophilic coatings that maximize the surface energy:
One method to prevent fogging is to apply a thin film of detergent, but this method is criticized because detergents are designed to be water-soluble and they cause smearing. Divers often use saliva, which is a commonly known and effective anti-fogging agent.
- Millbrooke, Anne (1998). ""More Favored than the Birds": The Manned Maneuvering Unit in Space". In Mack, Pamela E. From Engineering Science To Big Science. The NASA History Series. Archived from the original on 11 March 2010. Retrieved February 15, 2010.
- Hacker, Barton C.; Grimwood, James M. (1977). "An Angry Alligator". On the Shoulders of Titans: A History of Project Gemini. The NASA History Series. Archived from the original on 11 March 2010. Retrieved February 15, 2010.
- "My Experience as a Space Suit Test Subject". Retrieved February 15, 2010.
- "Antifogging agents for plastics". About.com. The New York Times Company. Retrieved February 15, 2010.
- Rick K.; "Burn". "Salclear Motorcycle Helmet Visor Anti-Fog". webBikeWorld.com. webWorld International. Archived from the original on 31 January 2010. Retrieved February 15, 2010.
- "Mask Care - Have a clear view every dive". The Scuba Doctor. The Scuba Doctor. Retrieved February 15, 2010.
- Dogey, Kent (July 26, 1991). "Mirror and method of mounting the same". Retrieved February 15, 2010.