Definition - What does Emulsion mean?

Emulsion is a suspension of tiny droplets of one liquid in a second liquid, such as an oil-in-water emulsion. An emulsion is thicker (has a higher viscosity) than either oil or water.

Emulsions are important in many fields, such as:

  • Dyeing and tanning industries
  • Manufacture of synthetic rubber and plastics
  • Preparation of cosmetics such as shampoos, salves and therapeutic products

Emulsions are part of a more general class of two-phase systems of matter called colloids. The terms colloid and emulsion are sometimes used interchangeably.

Corrosionpedia explains Emulsion

An emulsion is a colloid of two or more immiscible liquids where one liquid contains a dispersion of the other liquid(s). Oil and water mixtures are emulsions when shaken together. The oil forms drops and disperses throughout the water.

The term emulsion is often applied to mixed systems that should better be characterized as solutions, suspensions or gels. For example, so-called photographic emulsion is actually a gelatin gel in which tiny crystals of silver bromide are dispersed.

Emulsions consist of a dispersed and a continuous phase; the boundary between these phases is called the interface. Emulsions tend to have a cloudy appearance, because the many phase interfaces scatter light that passes through the emulsion. Emulsions are unstable and thus do not form spontaneously.

Emulsifying agents are effective at extinguishing fires on small, thin-layer spills of flammable liquids (class B fires). Such agents encapsulate the fuel in a fuel-water emulsion, thereby trapping the flammable vapors in the water phase.

Emulsions are stabilized by agents that form films at the surface of the droplets (such as soap molecules) or that impart to them a mechanical stability (such as colloidal carbon or bentonite). Unstable emulsions eventually separate into two liquid layers. Stable emulsions can be destroyed by inactivating or destroying the emulsifying agent — by methods like adding appropriate third substances or by freezing or heating.

Rust can occur if an emulsion breaks, in which case the instability of the emulsion renders the rust inhibitors ineffective. Broken and unstable emulsions are often caused by excessive bacterial contamination.

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