Emulsion and Suspension Science Glossary

This is a short glossary for terms and definitions of some of the terms used on this web-site, brochures, literature, and industry as a whole. It is not meant to cover every aspect of dispersion science. There are many excellent textbooks specializing for those interested in more detail.

Rather it is meant as a brief synopsis, and impetus -hopefully-, to think about dispersions as highly dynamic and complex systems; and encourage further research in this fascinating, however under apprecaited, field of science. We wish you good luck in your endeavors.

THE CONTENT OF THIS PAGE IS CURRENTLY BEING UPDATE.

Colloid Chemistry

Considering its importance and relevance to everyday life, colloid chemistry is a somewhat neglected and very much underappreciated term in todays world. Colloid comes from the greek word for glue. Its formal recoginition as an independent branch of science is attributed to Thomas Graham in the 1860's. Graham looked at the diffusivities of various substances and noted that while some showed large diffusion velocities (acids, salts), others did not (gelatin, albumin, silicic acid, aluminum hydroxide). The latter he also noted were very unstable. In his publication in the Proceedings of the Royal Society, June 16th, 1864, Graham notes that the hydrated silicic acid solution while remaing stable for days or weeks in a sealed tube, it was sure to gelatinize and become insoluble at last. He goes on to state that "the colloidal is, in fact a dynamic state of matter."

Colloidal Dispersion

The most straightforward and simplest definition of colloid dispersions is a two phase system, where on of the phases (named the dispersed phase) is dispersed in the second phase (called the continous phase). Though it should be noted that there are many systems consisting of 2 or more phases and each of the phases usually consists of multiple components. The dispersed phase can be made up of particles, droplets or bubbles. Ostwald (1907) proposed the following classification scheme for colloid dispersions: solid in gas, and liquid in gas are aerosols, solid in liquid are sols or dispersions, liquid in liqui are emulsions, and gas in liquids are foams. There are no exact size cutoffs when referring to colloidal dispersions, but generally ranges from nanometers up to tens of microns.

Emulsion:

By definition an emulsion is a system consisting of two immiscible liquids, one of which is dispersed in the other in the form of small droplets. Emulsion-based products are found within the chemical and agrochemical, cosmetic, pharmaceutical, and food industries. As emulsion structures are thermodynamically unstable, shelf-life stability Since the majority of emulsions contain water as one of the phases, it is customary to classify emulsions into two types: the oil-in-water (O/W) type consisting of droplets of oil dispersed in water, and the water-in-oil (W/O) type in which the phases are reversed. The continuous liquid is referred to as the dispersion medium, and the liquid which is in the form of droplets is called the disperse phase. Emulsions may be prepared readily by shaking together the two liquids or by adding one phase drop by drop to the other phase with some form of agitation, such as irradiation by ultrasonic waves of high intensity. In industry, emulsification is accomplished by means of emulsifying machines. The breaking of emulsions is necessary in many industrial operations, for example, in the separation of water-in-oil emulsions in the petroleum industry and in product recovery from emulsions produced by the steam distillation of organic liquids. Emulsions may be broken by (1) addition of multivalent ions of charge opposite to the emulsion droplet, (2) chemical action (addition of acids to emulsions stabilized by soaps), (3) freezing, (4) heating, (5) aging, (6) centrifuging, (7) application of high-potential alternating electric fields, and (8) treatment with ultrasonic waves of low intensity. See also Colloid; Soap.

Emulsion stability:

A stable emulsion consisting of two pure liquids cannot be prepared; to achieve stability, a third component, an emulsifying agent, must be present. Generally, the introduction of an emulsifying agent will lower the interfacial tension of the two phases. A large number of emulsifying agents are known; they can be classified broadly into several groups. The largest group is that of the soaps, detergents, and other compounds whose basic structure is a paraffin chain terminating in a polar group. Some solid powders can act as emulsifiers by being wetted more by one phase than by the other. Whichever phase shows the greater wetting power will become the dispersion medium. Many naturally occurring emulsions, such as milk or rubber latex, are stabilized by proteins. Egg yolk proteins stabilize mayonnaise and salad dressing. Certain hydrophilic colloids such as gum arabic or gelatin also stabilize water-in-oil emulsions by a similar mode of action.