Foam
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2008-07-11T16:46:43Z
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[[Image:Plankton creates sea foam 2.jpg|thumb|Close-up of sea foam on the [[tide pools]]]]
[[Image:Aluminium_foam.jpg|thumb|right|Foamed [[aluminium]]]]
[[Image:Foam - big.jpg|thumb|right|Soap foam bubbles]]
[[Image:FoamedPlastic.jpg|thumb|right|Some foamed plastic, up close.]]
The most general definition of '''foam''' is a substance that is formed by trapping many gas [[bubbles]] in a [[liquid]] or [[solid]]. It can also refer to anything that is analogous to such a phenomenon, such as [[quantum foam]]. Often the term is used in reference to [[polyurethane]] foam (foam rubber), [[Styrofoam]] or some other manufactured foam. It can be considered a type of [[colloid]].
From the early 20th century, various types of specially manufactured solid foams came into use. The low [[density]] of these foams made them excellent as thermal [[thermal insulation|insulator]]s and flotation devices, and their lightness and compressibility made them ideal as packing materials and stuffings. Some liquid foams, called [[fire retardant foam]]s, found use in extinguishing fires, especially [[oil fire]]s.
Foam, in this case meaning "bubbly liquid", is also produced as an often unwanted [[by-product]] in the manufacture of various substances. For example, foam is a serious problem in the [[chemical industry]], especially for [[biochemistry|biochemical]] processes. Many biological substances, for example [[protein]]s, easily create foam on [[agitation]] and/or [[aeration]]. Foam is a problem because it alters the liquid flow and blocks oxygen transfer from air (therefore preventing microbial respiration in [[aerobic respiration|aerobic]] [[fermentation (biochemistry)|fermentation]] processes). For this reason, [[anti-foaming agent]] compounds, like [[silicone]] oils, are added to prevent these problems.
If foaming is desired, a [[foaming agent]] may help.
Foaming around the mouth can be a symptom of [[rabies]] in animals. The term sea foam is used to describe the foam that forms on top of seawater from the action of waves. In some ways, leavened [[bread]] is a foam, as the [[yeast]] causes the bread to rise by producing tiny bubbles of gas in the dough.
==Structure of foams==
Real-life foams are typically disordered and have a variety of bubble sizes. The study of idealised foams is closely linked to the mathematical problems of [[space-filling]] and [[minimal surface]]s. The [[Weaire-Phelan structure]] is believed to be the best possible (optimal) [[unit cell]] of a perfectly ordered foam, while [[Plateau's laws]] describe how the soap-films form structures in foams.
Solid foams form an important class of lightweight cellular engineering materials. These foams can be classified into two types based on their pore structure. The first type of foams are called open cell structured foams. These foams contain pores that are connected to each other and form an interconnected network which is relatively soft. The second type of foams do not have interconnected pores and are called closed cell foams. Normally the closed cell foams have higher compressive strength due to their structures. Closed cell foams are also generally denser, requiring more material though and consequentially are more expensive to produce. The closed cells can be filled with a specialized gas to provide improved insulation. This is in contradistinction to the open cell foam which will fill with whatever it is surrounded with. While filled with air - this could be a relatively good insulator, however, if the open cells fill with water, insulative properties would be reduced.
A special class of closed cell foams is known as [[syntactic foam]], which contains hollow particles embedded in a matrix material.
The closed cell structure foams have higher dimensional stability, low moisture absorption coefficient and higher strength compared to open cell structured foams. All types of foams are widely used as core material in [[sandwich structured composite]] materials.
==See also==
*[[Beijing National Aquatics Centre]]
*[[Bubble]]
*[[Nanofoam]]
*[[Metal foam]]
==External links==
{{wiktionary|foam}}
{{commonscat|foam}}
*[http://oz.craftbrewer.org/Library/Methods/Other/KunzeFoam.shtml Beer foam]
*[http://aquafoam.com/ Aqueous foam technology]
*[http://foma-co.com/ Fomaco Foam production]
*[http://science.nasa.gov/headlines/y2003/09jun_foam.htm The strange physics of foam]
*[http://foammagazine.com Foam Magazine]
[[Category:Foams| ]]
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