Foam

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Foam

The most general definition of foam is a substance that is formed by trapping many gas bubbles in a liquid

Liquid

Liquid is one of the principal states of matter. A liquid is a fluid that has the particles loose and can freely form a distinct surface at the boundaries of its bulk material....
or solid

Solid

A solid object is in the states of matter characterized by resistance to deformation and changes of volume. In other words, it has high values both of Young's modulus and of shear modulus; this contrasts e.g....
. It can also refer to anything that is analogous to such a phenomenon, such as quantum foam

Quantum foam

Quantum foam, also referred to as spacetime foam, is a concept in quantum mechanics, devised by John Archibald Wheeler in 1955. The foam is supposedly the foundations of the fabric of the universe, but it can also be used as a qualitative description of subatomic spacetime turbulence at extremely small distances of the order of the...
. Often the term is used in reference to polyurethane

Polyurethane

A polyurethane, commonly abbreviated PU, is any polymer consisting of a chain of organic chemistry units joined by carbamate links. Polyurethane polymers are formed by reacting a monomer containing at least two isocyanate functional groups with another monomer containing at least two alcohol groups in the presence of a catalyst....
foam (foam rubber), XPS foam

Polystyrene

Polystyrene , sometimes abbreviated PS, is an Aromaticity polymer made from the aromatic monomer styrene, a liquid hydrocarbon that is commercially manufactured from petroleum by the chemical industry....
, Styrofoam

Styrofoam

Styrofoam is a trademark of Dow Chemical Company for presently made for thermal insulation and craft applications .In 1940, researchers in Dow's Chemical Physics Lab found a way to make foamed polystyrene....
or some other manufactured foam.

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Encyclopedia

The most general definition of foam is a substance that is formed by trapping many gas bubbles in a liquid

Liquid

Liquid is one of the principal states of matter. A liquid is a fluid that has the particles loose and can freely form a distinct surface at the boundaries of its bulk material....
or solid

Solid

Quantum foam

Polyurethane

Polystyrene

Styrofoam

Colloid

A colloid is a type of chemical mixture where one substance is dispersed evenly throughout another. The particles of the dispersed substance are only suspended in the mixture, unlike a solution, where they are completely dissolved within....
.

From the early 20th century, various types of specially manufactured solid foams came into use. The low density

Density

The density of a material is defined as its mass per unit volume. The symbol of density is ....
of these foams made them excellent as thermal insulator

Thermal insulation

The term thermal insulation can refer to materials used to reduce the rate of heat transfer, or the methods and processes used to reduce heat transfer....
s and flotation devices, and their lightness and compressibility made them ideal as packing materials and stuffings. Some liquid foams, called fire retardant foam

Fire retardant foam

Fire Retardant Foam, or fire suppression foam, is a foam used for fire extinguisher. Its role is to cool the fire and to coat the fuel, preventing its contact with oxygen, resulting in suppression of the combustion....
s, found use in extinguishing fires, especially oil fires.

Foam, in this case meaning "bubbly liquid", is also produced as an often unwanted by-product

By-product

A by-product is a secondary or incidental product deriving from a manufacturing process, a chemical reaction or a biochemical pathway, and is not the primary product or service being produced....
in the manufacture of various substances. For example, foam is a serious problem in the chemical industry

Chemical industry

The chemical industry comprises the companies that produce industrial chemicals. It is central to modern world economy, converting raw materials into more than 70,000 different products....
, especially for biochemical

Biochemistry

Biochemistry is the study of the chemistry processes in living organisms. It deals with the structure and function of cellular components such as proteins, carbohydrates, lipids, nucleic acids and other biomolecules....
processes. Many biological substances, for example protein

Protein

Proteins are organic compounds made of amino acids arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid Residue ....
s, easily create foam on agitation

Agitation

Agitation may refer to:* emotional state of excitement or restlessness** psychomotor agitation, an extreme form of the above, which can be a side effect of antipsychotic medication...
and/or aeration

Aeration

Aeration is the process by which air is circulated through, mixed with or solvation in a liquid or substance....
. Foam is a problem because it alters the liquid flow and blocks oxygen transfer from air (therefore preventing microbial respiration in aerobic fermentation

Fermentation (biochemistry)

Fermentation is the process of deriving energy from the Redox of organic compounds, such as carbohydrates, using an Endogeny electron acceptor, which is usually an organic compound....
processes). For this reason, anti-foaming agents, like silicone

Silicone

Silicones are largely inert, man-made compounds with a wide variety of forms and uses. Typically heat-resistant, nonstick, and rubberlike, they are commonly used in cookware, medicine, sealants, adhesives, lubricants, and insulation....
oils, are added to prevent these problems. Chemical methods of foam control are not always desired with respect to the problems (i.e. contamination

Contamination

Contamination is the presence of a minor constituent in another chemical or mixture, often at the trace level. In chemistry, the term usually describes a single chemical, but in specialized fields the term can also mean chemical mixtures, even up to the level of cellular materials....
, reduction of mass transfer

Mass transfer

Mass transfer is the transfer of mass from high concentration to low concentration. The phrase is commonly used in engineering for physical processes that involve molecule and convection transport of atoms and molecules within systems....
) they may cause especially in food and pharmaceutical industries where the product quality is of great importance. In order to prevent foam formation in such cases mechanical methods are mostly dominant over chemical ones.

If foaming is desired, a foaming agent

Foaming agent

A foaming agent is a surfactant, which when present in small amounts, facilitates the formation of a foam, or enhances its colloid stability by inhibiting the Coalescence of bubbles....
may help.

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

Bread

Bread is a staple food prepared by baking a dough of flour and water. It may be leavened or unleavened. Edible salt, fat and a leavening agent such as yeast are common ingredients, though bread may contain a range of other ingredients: milk, Egg , sugar, spice, fruit , vegetables , Nut or seeds ....
is a foam, as the yeast

Yeast

Yeasts are eukaryote microorganisms classified in the Kingdom fungus, with about 1,500 species currently described; they dominate fungal diversity in the oceans....
causes the bread to rise by producing tiny bubbles of gas in the dough.

The unique property of gas-liquid foams having very high specific surface area are exploited in the chemical processes of froth flotation

Froth flotation

Froth flotation is a process for selectively separating hydrophobic materials from hydrophilic. This is used in several processing industries. Historically this was first used in the mining industry....
and foam fractionation

Foam fractionation

Foam fractionation is a chemical process in which hydrophobic molecules are Separation process from a solution using rising columns of foam. It is commonly used, albeit on a small scale, for the removal of organic waste from aquaria; these units are known as 'protein skimmers'....
.

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

Minimal surface

In mathematics, a minimal surface is a surface with a mean curvature of zero.These include, but are not limited to, surfaces of minimum area subject to various constraints....
s. The Weaire-Phelan structure

Weaire-Phelan structure

The Weaire-Phelan structure is a complex 3-dimensional structure. In 1993, Denis Weaire and Robert Phelan, two physicists based at Trinity College Dublin found that in computer simulations of foam, this structure was a better solution of the "Kelvin problem" than the previous best-known solution, the Kelvin structure....
is believed to be the best possible (optimal) unit cell of a perfectly ordered foam, while Plateau's laws

Plateau's laws

Plateau's Rules describe the structure of soap films in forms. These rules were formulated in the 19th century by the Belgian physicist Joseph Plateau from his experimental observations....
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. However, closed cell foams are also generally denser, require more material, 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. If filled with air this could be a relatively good insulator, but if the open cells fill with water, insulation properties would be reduced.

A special class of closed cell foams is known as syntactic foam

Syntactic foam

Syntactic foams are composite materials synthesized by filling a metal, polymer or ceramic matrix with hollow particles called microballoons. The presence of hollow particles results in lower density, higher strength, a lower thermal expansion coefficient, and, in some cases, stealth technology....
, which contains hollow particles embedded in a matrix material.

The closed cell structure foams have higher dimensional stability, low moisture absorption coefficients and higher strength compared to open cell structured foams. All types of foam are widely used as core material in sandwich structured composite

Sandwich structured composite

A sandwich structured composite is a special class of composite materials that is fabricated by attaching two thin but stiff skins to a lightweight but thick core....
materials.

Foam

Structure of foams

See also

External links