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Unformatted text preview: ulsion stabilized with SDS,
a nearly monodisperse emulsion The droplets are usually from 0.1 to 1 µm in diameter (larger than sol parti cle s ) . Emu l s io n s
are generally unstable unless a third substance, known as an emulsifying agent o r a
stabilizing agent, is present.
Soaps and detergents are effect i v e e mu l s i fying agents, particul arly for oil-water
5 e muls i on s. They con s ist of long-chain hydrocarbon molecules each having at one end
a polar group such as a carboxylic acid or sulfonic acid group. These molecules are
readily adsorbed at oil-water interfaces. The hydrocarbon chains become attached to
the oil and the polar g r oups to the wa t er .
T he term micelle (Latin micella, small crumb,
diminutive of the Latin mica, crumb) was
used t o refer to pa rticles that ar e stabilized by
• The action of emulsifying agents is to
reduce the interfacial tension between
the two phases, to cause the surface to become as small as possible.
A high surface tension between the disperse phase and the dispersion medium
will therefore tend to cause an emuls i o n t o se pa rate i nto t wo bulk phases (i.e.,
The adsorption of an emulsifying agent on an interface reduces this tension and
therefore decreases the tendency of the emulsion to coagulate.
An emulsion with no stabilizing agent has properties similar to those of
lyophobic sols (they are easily coagulated by electrolytes).
Stabilized emulsions behave more like lyophilic sols and are only affected by
electrolytes at high concentrations. 6...
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