FOAM DEFINITION - A foam is a substance made by trapping air or gas bubbles inside a solid or liquid. Another definition of foam is a bubbly liquid, particularly if the bubbles, or froth, are undesirable. Foam can impede the flow of a liquid and block gas exchange with air. Anti-foaming agents may be added to a liquid to help prevent bubbles from forming. The term foam may also refer to other phenomena that resemble foams, such as foam rubber and quantum foam. Rising bread dough may be considered a semisolid foam. Solid foams include dry wood, polystyrene foam, memory foam, and mat foam (as for camping and yoga mats). It's also possible to make a foam using metal.

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Foam Definition in Chemistry

What Is Foam in Chemistry Terms?

by Anne Marie Helmenstine, Ph.D. 

A foam is a substance made by trapping air or gas bubbles inside a solid or liquid.

Typically, the volume of gas is much larger than that of the liquid or solid, with thin films separating gas pockets.

Another definition of foam is a bubbly liquid, particularly if the bubbles, or froth, are undesirable.

Foam can impede the flow of a liquid and block gas exchange with air. Anti-foaming agents may be added to a liquid to help prevent bubbles from forming.

The term foam may also refer to other phenomena that resemble foams, such as foam rubber and quantum foam.

How Foam Forms

Three requirements must be met in order for foam to form. Mechanical work is needed to increase the surface area.

This can occur by agitation, dispersing a large volume of gas into a liquid, or injecting a gas into a liquid.

The second requirement is that surfactants or surface active components must be present to decrease surface tension.

Finally, the foam must form more quickly than it breaks down.

Foams may be open-cell or closed-cell in nature. Pores connect the gas regions in open-cell foams, while closed-cell foams have enclosed cells.

The cells are usually disordered in their arrangement, with varying bubble sizes. The cells present minimal surface area, forming honeycomb shapes or tessellations.

Foams are stabilized by the Marangoni effect and by van der Waals forces.

The Marangoni effect is a mass transfer along the interface between fluids due to surface tension gradient.

In foams, the effect acts to restore lamellae (a network of interconnected films).

Van der Waals forces form electric double layers when dipolar surfactants are present.

Foams are destabilized as gas bubbles rise through them. Also, gravity pulls liquid downward in a liquid-gas foam.

Osmotic pressure drains lamellae because of concentration differences throughout the structure. Laplace pressure and disjoining pressure also act to destabilize foams.

Examples of Foam

Examples of foams formed by gases in liquids include whipped cream, fire retardant foam, and soap bubbles.

Rising bread dough may be considered a semisolid foam. Solid foams include dry wood, polystyrene foam, memory foam, and mat foam (as for camping and yoga mats). It's also possible to make a foam using metal.

Foam Uses

Bubbles and bath foam are fun uses of foam, but it has many practical uses, too.

·          Fire retardant foam is used to extinguish fires.

·          Solid foams may be used to engineer strong yet light materials.

·         Solid foams are excellent thermal insulators.

·          Solid foams are used to make flotation devices.

·         Because solid foams are light and compressible, they make an excellent stuffing and packing material.

·         A closed-cell foam called a syntactic foam consists of hollow particles in a matrix. This type of foam is used to make shape memory resins. Syntactic foams are also used in space and deep-sea exploration.

·         Self-skin or integral skin foam consists of a dense skin with a lower density core. This type of foam is used to make shoe soles, mattresses, and baby seats.

Anne Marie Helmenstine, Ph.D.

Introduction

Ph.D. in biomedical sciences from the University of Tennessee at Knoxville - Oak Ridge National Laboratory.

Science educator with experience teaching chemistry, biology, astronomy, and physics at the high school, college, and graduate levels.

ThoughtCo and About Education chemistry expert since 2001.

Widely-published graphic artist, responsible for printable periodic tables and other illustrations used in science.

Experience

Anne Helmenstine, Ph.D. has covered chemistry for ThoughtCo and About Education since 2001, and other sciences since 2013. She taught chemistry, biology, astronomy, and physics at the high school, college, and graduate levels. She has worked as a research scientist and also abstracting and indexing diverse scientific literature for the Department of Energy.

In addition to her work as a science writer, Dr. Helmenstine currently serves as a scientific consultant, specializing in problems requiring an interdisciplinary approach. Previously, she worked as a research scientist and college professor. 

Education

Dr. Helmenstine holds a Ph.D. in biomedical sciences from the University of Tennessee at Knoxville and a B.A. in physics and mathematics with a minor in chemistry from Hastings College. In her doctoral work, Dr. Helmenstine developed ultra-sensitive chemical detection and medical diagnostic tests.

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https://www.thoughtco.com/definition-of-foam-605140