December 14, 2023 in 

An emulsion is the result of mixing two or more immiscible liquids, in which one component disperses into another through very fine droplets. Emulsions belong to the class of two-phase systems known as colloids and should only be considered an emulsion when both spread and continuous phases are liquid. Although colloids and emulsion are often used interchangeably, in an emulsion, one component disperses into both successive phases; distributed components do not settle out from either phase; sufficient interfacial tension exists between both phases to prevent their separation; dispersed-phase droplets typically range between 1 micrometer (um).

Emulsion derives its name from the Latin “lac,” the most well-known emulsion type. Milk is composed of fat droplets in water; butter contains water-in-fat, while margarine contains oil in fat form. Emulsions are used extensively throughout food products like mayonnaise, salad dressings, sandwich spreads, and ice cream and can even be found in cosmetics and pharmaceutical products.

Many factors can destabilize an emulsion and cause its dispersed phase to aggregate and separate from its continuous phase, such as temperature or pH fluctuations, the addition of certain compounds, or mechanical agitation.

Emulsions are used in printing to produce half-tones (variations in shade of gray) and color photographs. Lithography involves dispersing an oil-based ink into water before applying it to a printing plate. Hydrophobic (water-repelling) ink adheres to its surface, while hydrophilic water (attracting) water dissipates over time, eventually being transferred from the printing surface onto paper sheets through ink transference.

In intaglio printing techniques like engraving and etching, an emulsion of wax or resin is used to protect areas of the printing plate that do not need to be printed. After applying ink to these areas of the plate, the excess is removed before being set onto a press where paper passes over it, picking up ink from any engravings or etchings on its way through.

Offset lithography uses printing plates coated with light-sensitive material after exposure to light, which hardens only those areas intended to remain white on the plate’s light-sensitive coating and later develops by stripping away unhardened areas.

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