The colloids they are inhomogeneous mixtures made up of a dispersed phase, which is almost always a solid with very small particles, and a dispersing or continuous phase, which is generally liquid or gaseous. For instance: heavy cream, latex paint, jelly.
There may also be colloids in which both phases are in any of the three states of aggregation, except that both phases are gaseous (if both phases are gases, it will not be a colloid but a solution).
The word colloid was introduced by the Scottish chemist Thomas graham in 1861 and is derived from the Greek root kolas (κoλλα), which means “sticky” or “unctuous”. This is related to the property of this type of substance of not passing through the usual filters.
When a beam of light passes through a colloid, it scatters and becomes visible. This event is known as Tyndall effect. The presence of this optical effect makes it possible to distinguish a colloid from a solution or solution. Colloid particles have a diameter between 1 nanometer and a micrometer; that of the solutions are smaller than 1 nanometer and those of the suspensions are greater than 1 micrometer. Colloids have properties intermediate between solutions and suspensions.
Types of colloids
In case the dispersing phase is water, the colloids can be hydrophilic (attraction of its particles with water) or hydrophobic (repulsion of its particles with water).
If the dispersing phase is liquid, the colloids can be lyophobes or lyophilic. In lyophobes there is little attraction between the dispersed phase and the dispersant phase. On the other hand, in lyophiles there is a lot of attraction between both phases.
The physical state of the colloid is generally defined by the physical state of the dispersing phase, which can be liquid, solid or gaseous. The dispersed phase can also correspond to one of these three types, although in gaseous colloids this is always a liquid or a solid.
Colloids can also be classified into:
- Suns. They are colloids in which the dispersing phase is liquid. When they are lyophobic, they can coagulate with increasing temperature.
- Aerosol sprays. The dispersant phase is a gas and the dispersed phase can be very small particles of a liquid or a solid.
- Gases. They are formed by the transition from a sol to a gel through a gradual process called gelation.
- Foams. The dispersant phase can be a liquid or a solid and the dispersed phase is a gas.
- Emulsions. The dispersant phase is a liquid and the dispersed phase is a liquid immiscible with it. These colloids are suspensions of two liquids.
Uses of colloids
Colloidal substances are important in the formulation of numerous industrial materials of habitual and massive use as paints, plastics, insecticides for agriculture, inks, cements, soaps, lubricants, detergents, adhesives and various food products. The colloids contained in the soil contribute to its retention of water and nutrients.
In medicine, colloids or plasma expanders to expand intravascular volume for longer periods than is achieved through the use of crystalloids.
List of examples of colloids
- Organic material
- Milk cream
- Latex paints
- Montmorillonite and other silicate clays
- Bovine cartilage
- Albumin derivatives
- Hydroethyl starches
- Woven bone
- Silica gel
- Titanium oxide