A foam is a substance that is formed by trapping pockets of gas in a liquid or solid. A bath sponge and the head on a glass of beer are examples of foams. In most foams, the volume of gas is large, with thin films of liquid or solid separating the regions of gas.
An important division of solid foams is into closed-cell foams and open-cell foams. In a closed-cell foam, the gas forms discrete pockets, each completely surrounded by the solid material. In an open-cell foam, the gas pockets connect with each other. A bath sponge is an example of an open-cell foam: water can easily flow through the entire structure, displacing the air. A camping mat is an example of a closed-cell foam: the gas pockets are sealed from each other, and so the mat cannot soak up water.
Foams are examples of dispersed media. In general, gas is present in large amount so it will be divided in gas bubbles of many different sizes (the material is polydisperse) separated by liquid regions which may form films, thinner and thinner when the liquid phase is drained out of the system films. When the principal scale is small, i.e. for a very fine foam, this dispersed medium can be considered as a type of colloid.
The term foam may also refer to anything that is analogous to such a foam, such as quantum foam, polyurethane foam (foam rubber), XPS foam, Polystyrene, phenolic, or many other manufactured foams. This is not the purpose of this page.
Other articles related to "foam":
... Spray foam is a very specialised packing material, often required for use in shipping valuable fragile items ... By virtue of the liquid foam expanding by up to 280 times the volume of its liquid state, it efficiently protects almost any size, form and weight ...
... Foam has often been applied to the underside of timber framed roofs, primarily as a cure for slate slippage on old roofs with decaying nails ... The foam makes inspection of the timber structure impractical ... The adhesion between foam and slate also makes later reuse of the slates impossible, adding significant extra cost to the eventual reroof ...
... Polyurethane, the most common type of spray foam insulation, was developed and used by the military in the 1940s and applied to airplanes ... It wasn't until the 1970s that it started to be used as foam insulation ... Various systems are used to apply the spray foam ...
... drink prepared with espresso, hot milk, and steamed milk foam ... or textured milk than the caffè latte with the total of espresso and milk/foam making up between approximately 150 and 180 millilitres (5 and 6 US fluid ounces) ... exceeds the height of the cup, making the foam visible above the side of the cup ...
... Foam scales and properties Scale Generation Structure Stability Dynamic Experiments and characterization Transport properties Irisations Maths Applications Fun Surfactants ...
Famous quotes containing the word foam:
“Only the white, tremendous foam of the street has any importance,
The new white flowers that are beginning to shoot up about now.”
—John Ashbery (b. 1927)
“To dine! she shrieked in dragon-wrath.
To swallow wines all foam and froth!
To simper at a table-cloth!
Say, can thy noble spirit stoop
To join the gormandising troop
Who find solace in the soup?”
—Lewis Carroll [Charles Lutwidge Dodgson] (18321898)