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What are emulsions : examples, features, preparation & measurement

What are emulsions?


Emulsions are dispersions of two immiscible liquids. They are of interest in many important practical applications in the food, cosmetic, oil production, agriculture, chemical, oil & gas, pharmaceuticals and several other process industries.


There are two types of emulsions: Oil-in-water (O/W) type, where oil forms the dispersed (droplets) phase and water forms the continuous phase; and water-in-oil (W/O) type, where water forms the dispersed (droplets) phase and oil forms the continuous phase. Without an effective interfacial stabilizer, emulsions are unstable systems and they readily separate out into oil and water phases as the mechanical agitation is stopped.

One of the most important of emulsions is their inherent instability. Though the dispersed drops are small, gravity exerts a measurable force on them and overtime they coalesce to form larger drops which tend to either settle to the bottom or rise to the top of the mixture. This process ultimately causes the internal and external phases to separate into the two original components. Depending on how the emulsion is formulated and the physical environment to which it is exposed, this separation may take minutes, months, or millennia.


Key points and features of emulsions

  • An emulsion is a type of colloid formed by combining two liquids that normally don’t mix.
  • In an emulsion, one liquid contains a dispersion of the other liquid.
  • The process of mixing liquids to form an emulsion is called emulsification.
  • Even though the liquids that form them may be clear, emulsions appear cloudy or colored because light is scattered by the suspended particles in the mixture.
  • Safety and environmental friendliness ensured by using water as a solvent
  • Viscosity can be easily adjusted
  • Suitability for gluing and coating applications derived from emulsion’s property of forming a film when dried
  • Excellent miscibility with pigments, solvents, additives, etc

Preparing emulsions

An emulsion is prepared by shaking strongly the mixture of the two liquids or by passing the mixture through a colloid mill known as the homogenizer. The emulsions thus prepared from the pure liquids are usually not stable and the two liquids separate out on standing. To get a stable emulsion, small quantities of certain other substances are added during preparation. The substances thus added to stabilize the emulsions are called emulsifiers or emulsifying agents. The substances commonly used as emulsifying agents are soaps of various kinds, long chain sulphonic acids or lyophilic colloids like proteins, gum, and agar.

Emulsions may be prepared by several methods, depending upon the nature of the components and the equipment. On a small scale, as in the laboratory or pharmacy, emulsions may be prepared using a dry Wedgwood or porcelain mortar and pestle or a mechanical blender or mixer. On a large scale, large mixing tanks may be used to form the emulsion through the action of a high-speed impeller.

Emulsions - preparation in industries - tanks and mixers

Viscosity of emulsions

  • The viscosity of emulsions varies depending on the temperature.
  • As the temperature decreases, the viscosity increases.
  • By adding water, the viscosity can be adjusted to a lower viscosity
  • To increase the viscosity, emulsion thickeners may be used