A colloid is the end result of dispersing one substance evenly and microscopically in another without any changes in the structure of either. Colloids are distinct from other combinations such as solutions due to the fact that none of the constituent parts of the union dissolve or experience any structural changes during dispersal. Colloids may exist in combinations of all the matter states including gaseous, liquid, and solid unions. In an emulsified state, colloid unions may consist of one or more immiscible constituents where surfactants maintain even distribution of the individual parts. Some well known examples of colloids are milk and fog.
Mixtures or unions of different materials and substances exist in a variety of forms. In most, one or more of the individual parts of the mixture undergo some sort of physical or chemical change. Unlike combinations such as solvents and alloys, colloid mixtures feature an even distribution of all constituent parts in their original, unchanged form. This means that colloids deliver the individual characteristics of all their parts and not a reactive combination of qualities. In this way, active ingredients can be suspended in inert carrier mediums without changing or negatively affecting their characteristics.
Colloid mixtures consist of two distinct parts: a dispersed phase or substance and a dispersal medium. Milk, as an example, is a colloid consisting of a liquid butterfat dispersal phase distributed in a water based dispersal medium. Colloids may consist of combinations of all matter states with common unions including liquid/air mixtures such as fog and mist and solid/air unions such as smoke or cloud masses. Other common combinations include liquid/gas mixes such as whipped cream, liquid/solid gel combinations such as gelatin, and solid/liquid dispersals which include blood and inks. Decorative cranberry glass is an example of a solid/solid colloid and is a combination of red glass and gold chloride.
The individual parts of liquid/liquid colloids are not always miscible or mixable and would gradually separate after combination if no additional additives were introduced. These additives are known as surfactants and alter the surface tension characteristics of the mixture which encourages the immiscible components to remain evenly dispersed. Milk is one of the best known examples of these unions or emulsions. Colloids may also be formulated to exhibit unstable, fractional qualities which allow them to flow when exposed to stress, and then regain cohesion once the stress is ceased. One example of this phenomenon is toothpaste, which flows when the tube is squeezed and then remains stable on the toothbrush.