Emulsion

This article is about mixtures of liquids. For the light-sensitive mixture used in photography, see Photographic emulsion.
  1. Two immiscible liquids, not yet emulsified
  2. An emulsion of Phase II dispersed in Phase I
  3. The unstable emulsion progressively separates
  4. The surfactant (outline around particles) positions itself on the interfaces between Phase II and Phase I, stabilizing the emulsion

An emulsion is a mixture of two or more liquids that are normally immiscible (unmixable or unblendable) owing to liquid-liquid phase separation. 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 should be used when both phases, dispersed and continuous, are liquids. In an emulsion, one liquid (the dispersed phase) is dispersed in the other (the continuous phase). Examples of emulsions include vinaigrettes, homogenized milk, liquid biomolecular condensates, and some cutting fluids for metal working.

Two liquids can form different types of emulsions. As an example, oil and water can form, first, an oil-in-water emulsion, in which the oil is the dispersed phase, and water is the continuous phase. Second, they can form a water-in-oil emulsion, in which water is the dispersed phase and oil is the continuous phase. Multiple emulsions are also possible, including a "water-in-oil-in-water" emulsion and an "oil-in-water-in-oil" emulsion.[1]

Emulsions, being liquids, do not exhibit a static internal structure. The droplets dispersed in the continuous phase (sometimes referred to as the "dispersion medium") are usually assumed to be statistically distributed to produce roughly spherical droplets.

The term "emulsion" is also used to refer to the photo-sensitive side of photographic film. Such a photographic emulsion consists of silver halide colloidal particles dispersed in a gelatin matrix. Nuclear emulsions are similar to photographic emulsions, except that they are used in particle physics to detect high-energy elementary particles.

IUPAC

A fluid system in which liquid droplets are dispersed in a liquid.

Note 1: The definition is based on the definition in ref.[2]

Note 2: The droplets may be amorphous, liquid-crystalline, or any
mixture thereof.

Note 3: The diameters of the droplets constituting the dispersed phase
usually range from approximately 10 nm to 100 μm; i.e., the droplets
may exceed the usual size limits for colloidal particles.

Note 4: An emulsion is termed an oil/water (o/w) emulsion if the
dispersed phase is an organic material and the continuous phase is
water or an aqueous solution and is termed water/oil (w/o) if the dispersed
phase is water or an aqueous solution and the continuous phase is an
organic liquid (an "oil").

Note 5: A w/o emulsion is sometimes called an inverse emulsion.
The term "inverse emulsion" is misleading, suggesting incorrectly that
the emulsion has properties that are the opposite of those of an emulsion.
Its use is, therefore, not recommended.[3]

  1. ^ Khan, A. Y.; Talegaonkar, S; Iqbal, Z; Ahmed, F. J.; Khar, R. K. (2006). "Multiple emulsions: An overview". Current Drug Delivery. 3 (4): 429–43. doi:10.2174/156720106778559056. PMID 17076645.
  2. ^ IUPAC (1997). "Emulsion". Compendium of Chemical Terminology (The "Gold Book"). Oxford: Blackwell Scientific Publications. doi:10.1351/goldbook.E02065. ISBN 978-0-9678550-9-7. Archived from the original on 2012-03-10.{{cite book}}: CS1 maint: bot: original URL status unknown (link)
  3. ^ Slomkowski, Stanislaw; Alemán, José V.; Gilbert, Robert G.; Hess, Michael; Horie, Kazuyuki; Jones, Richard G.; Kubisa, Przemyslaw; Meisel, Ingrid; Mormann, Werner; Penczek, Stanisław; Stepto, Robert F. T. (2011). "Terminology of polymers and polymerization processes in dispersed systems (IUPAC Recommendations 2011)" (PDF). Pure and Applied Chemistry. 83 (12): 2229–2259. doi:10.1351/PAC-REC-10-06-03. S2CID 96812603.