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Dispersed media
Encyclopedia
A dispersed medium consists of two media that do not mix. More specifically, it contains discrete elements of one medium which are dispersed in a continuous second medium. The two media can be of very different nature. In particular, they can be a gas
, a liquid
or a solid
.
Many materials which we encounter during the day are dispersed media. For example, milk
consists of oil
drops dispersed in water, fog
contains tiny water drops dispersed in air, shaving cream
contains bubbles dispersed in a liquid, sand consists of solid grains in air and a kitchen sponge of bubbles dispersed in a solid.
Dispersed media are commonly classified according to the nature of the two media and the volume fraction of the dispersed medium. At very low volume fraction the dispersed objects are not in contact with each other. At intermediate volume fraction they start to be in contact (they jam
). And at even higher volume fraction, the dispersed objects deform in a tight packing.
Another classification takes into account the typical size of the dispersed objects. When the objects are very small (typically < 1 micrometer), for example, one speaks of colloids.
The following table provides an overview of the main types of dispersed media.
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
, a liquid
Liquid
Liquid is one of the three classical states of matter . Like a gas, a liquid is able to flow and take the shape of a container. Some liquids resist compression, while others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly...
or a solid
Solid
Solid is one of the three classical states of matter . It is characterized by structural rigidity and resistance to changes of shape or volume. Unlike a liquid, a solid object does not flow to take on the shape of its container, nor does it expand to fill the entire volume available to it like a...
.
Many materials which we encounter during the day are dispersed media. For example, milk
Milk
Milk is a white liquid produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals before they are able to digest other types of food. Early-lactation milk contains colostrum, which carries the mother's antibodies to the baby and can reduce the risk of many...
consists of oil
Oil
An oil is any substance that is liquid at ambient temperatures and does not mix with water but may mix with other oils and organic solvents. This general definition includes vegetable oils, volatile essential oils, petrochemical oils, and synthetic oils....
drops dispersed in water, fog
Fog
Fog is a collection of water droplets or ice crystals suspended in the air at or near the Earth's surface. While fog is a type of stratus cloud, the term "fog" is typically distinguished from the more generic term "cloud" in that fog is low-lying, and the moisture in the fog is often generated...
contains tiny water drops dispersed in air, shaving cream
Shaving cream
Shaving cream is a substance that is applied to the face or wherever else hair grows, to provide lubrication and avoid razor burn during shaving. Shaving cream is often bought in a spray can, but can also be purchased in tubs or tubes. Shaving cream in a can is commonly dispensed as a foam or a gel...
contains bubbles dispersed in a liquid, sand consists of solid grains in air and a kitchen sponge of bubbles dispersed in a solid.
Dispersed media are commonly classified according to the nature of the two media and the volume fraction of the dispersed medium. At very low volume fraction the dispersed objects are not in contact with each other. At intermediate volume fraction they start to be in contact (they jam
Jamming (physics)
Jamming is the physical process by which some materials, such as granular materials, glasses, foams, and other complex fluids, become rigid with increasing density...
). And at even higher volume fraction, the dispersed objects deform in a tight packing.
Another classification takes into account the typical size of the dispersed objects. When the objects are very small (typically < 1 micrometer), for example, one speaks of colloids.
The following table provides an overview of the main types of dispersed media.
Medium | Dispersed medium | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Continuous medium | Gas | (All gases are mutually miscible Miscibility Miscibility is the property of liquids to mix in all proportions, forming a homogeneous solution. In principle, the term applies also to other phases , but the main focus is usually on the solubility of one liquid in another... ) |
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Liquid |
| Emulsion An emulsion is a mixture of two or more liquids that are normally immiscible . Emulsions are part of a more general class of two-phase systems of matter called colloids. Although the terms colloid and emulsion are sometimes used interchangeably, emulsion is used when both the dispersed and the...
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Solid |
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