Anti-fog agents, also known as anti-fogging agents and treatments, are chemicals that prevent the

condensation Condensation is the change of the state of matter from the gas phase into the liquid phase, and is the reverse of vaporization. The word most often refers to the water cycle. It can also be defined as the change in the state of water vapor ...

water Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...

in the form of small

droplets A drop or droplet is a small column of liquid, bounded completely or almost completely by free surfaces. A drop may form when liquid accumulates at the end of a tube or other surface boundary, producing a hanging drop called a pendant drop. Dro ...

on a surface which resemble

fog Fog is a visible aerosol consisting of tiny water droplets or ice crystals suspended in the air at or near the Earth's surface. Reprint from Fog can be considered a type of low-lying cloud usually resembling stratus and is heavily influenc ...

. They are one of many

additives Additive may refer to: Mathematics * Additive function, a function in number theory * Additive map, a function that preserves the addition operation * Additive set-function see Sigma additivity * Additive category, a preadditive category with fin ...

used in the production of plastics.

Development

Anti-fog agents were developed by

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

during the

Project Gemini Project Gemini () was the second United States human spaceflight program to fly. Conducted after the first American crewed space program, Project Mercury, while the Apollo program was still in early development, Gemini was conceived in 1961 and ...

, for use on helmet

visor A visor (also spelled vizor) is a surface that protects the eyes, such as shading them from the sun or other bright light or protecting them from objects. Nowadays many visors are transparent, but before strong transparent substances such a ...

s. During

Gemini 9A Gemini 9A (officially Gemini IX-A) With Gemini IV, NASA changed to Roman numerals for Gemini mission designations. was a 1966 crewed spaceflight in NASA's Gemini program. It was the seventh crewed Gemini flight, the 15th crewed American flight ...

, in June 1966, Astronaut Eugene A. Cernan tested NASA's first

space suit A space suit (or spacesuit) is an environmental suit used for protection from the harsh environment of outer space, mainly from its vacuum as a highly specialized pressure suit, but also its temperature extremes, as well as radiation and ...

, 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

. Later Gemini flights all included the anti-fog solution, for application prior to the space walk occurring.

Application

Anti-fog agents are available as

spray Spray or spraying commonly refer to: * Spray (liquid drop) ** Aerosol spray ** Blood spray ** Hair spray ** Nasal spray ** Pepper spray ** PAVA spray ** Road spray or tire spray, road debris kicked up from a vehicle tire ** Sea spray, refers to ...

solution Solution may refer to: * Solution (chemistry), a mixture where one substance is dissolved in another * Solution (equation), in mathematics ** Numerical solution, in numerical analysis, approximate solutions within specified error bounds * Solu ...

cream Cream is a dairy product composed of the higher-fat layer skimmed from the top of milk before homogenization. In un-homogenized milk, the fat, which is less dense, eventually rises to the top. In the industrial production of cream, this proces ...

s and gels, and

wet wipe A wet wipe, also known as a wet towel, wet one, moist towelette, disposable wipe, disinfecting wipe, or a baby wipe (in specific circumstances) is a small to medium-sized moistened piece of plastic or cloth that either comes folded and individu ...

s, while more resistant

coating A coating is a covering that is applied to the surface of an object, or substrate. The purpose of applying the coating may be decorative, functional, or both. Coatings may be applied as liquids, gases or solids e.g. powder coatings. Paints ...

s are often applied during complex

manufacturing Manufacturing is the creation or production of goods with the help of equipment, labor, machines, tools, and chemical or biological processing or formulation. It is the essence of the secondary sector of the economy. The term may refer ...

processes. Anti-fog additives can also be added to plastics where they exude from the inside to the surface.

Agents

Most commercial anti-fog agents are

surfactant Surfactants are chemical compounds that decrease the surface tension or interfacial tension between two liquids, a liquid and a gas, or a liquid and a solid. The word ''surfactant'' is a Blend word, blend of "surface-active agent", coined in ...

s that minimize the surface tension of the water. Ethoxylates and

polysiloxane In organosilicon and polymer chemistry, a silicone or polysiloxane is a polymer composed of repeating units of siloxane (, where R = organic group). They are typically colorless oils or rubber-like substances. Silicones are used in sealants ...

s are typical. Many other substances have been used as anti-fog agents including home-based recipes containing

detergent A detergent is a surfactant or a mixture of surfactants with Cleanliness, cleansing properties when in Concentration, dilute Solution (chemistry), solutions. There are a large variety of detergents. A common family is the alkylbenzene sulfonate ...

s. One method to prevent fogging is to apply a thin film of

, but this method is criticized because detergents are designed to be

water-soluble In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solub ...

and they cause smearing. Divers often use saliva, which is a commonly known and effective anti-fogging agent.

Uses

Underwater diving

A demister is a substance applied to transparent surfaces to stop them from becoming fogged with mist deposit, often referred to as fog.

Scuba divers Scuba diving is a mode of underwater diving whereby divers use breathing equipment that is completely independent of a surface breathing gas supply, and therefore has a limited but variable endurance. The word ''scuba'' is an acronym for ...

often spit into their masks and then wash the surface quickly with water to prevent mist buildup that can impair vision. Several products are commercially available such as Sea Drops that are generally more effective. New masks lenses still have

silicone In Organosilicon chemistry, organosilicon and polymer chemistry, a silicone or polysiloxane is a polymer composed of repeating units of siloxane (, where R = Organyl group, organic group). They are typically colorless oils or elastomer, rubber ...

on them from the manufacturing process, so it is recommended to clean the lenses with an appropriate mask scrub, then rinse the mask and then apply a demister solution.

References