Colloids are non – homogeneous mixtures composed of a dispersed phase, which is almost always a solid with very small particles, and a dispersing or continuous phase, which is usually liquid or gaseous . For example: cream, latex paint, gelatin .
There may also be colloids in which both phases are in any of the three states of aggregation, except if they are both gaseous phases (if both phases are gases, it will not be a colloid but a solution ).
The word “colloid” was coined by Scottish chemist Thomas Graham in 1861 and is derived from the Greek root kolas (κoλλα), meaning “adherent” or “unctuous.” This relates to the property of these substances to avoid passing through conventional filters.
When a light beam passes through a colloid, it disperses and becomes visible. This phenomenon is known as the Tyndall effect. The presence of this optical effect allows a colloid to be distinguished from a solution. Colloid particles have a diameter between 1 nanometer and 1 micrometer; those of solutions are less than 1 nanometer, and those of suspensions are greater than 1 micrometer. Colloids have properties that are intermediate between those of solutions and suspensions .
- It may be useful for you: Gels
Types of colloids
If the dispersing phase is water, colloids can be hydrophilic (attraction of their particles to water) or hydrophobic (repulsion of their particles to water).
If the dispersing phase is liquid, colloids can be lyophobic or lyophilic . In lyophobic colloids, there is little attraction between the dispersed phase and the dispersing phase. On the other hand, in lyophilic colloids, there is a strong attraction between the two phases.
The physical state of a 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 it is always a liquid or a solid.
Colloids can also be classified into:
- Sols. These are colloids in which the dispersing phase is liquid. When they are lyophobic, they can coagulate when the temperature increases .
- Aerosols. The dispersing 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 of a sol to a gel through a gradual process called gelation.
- Foams. The dispersing phase can be a liquid or a solid, and the dispersed phase is a gas.
- Emulsions. The dispersing 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 commonly used industrial materials, such as paints, plastics, agricultural insecticides , inks, cements, soaps, lubricants, detergents, adhesives, and various food products. The colloids contained in soil contribute to its water and nutrient retention .
In medicine, colloids or plasma expanders are administered to expand intravascular volume for longer periods than what is achieved with the use of crystalloids.
List of examples of colloids
- Plasma
- Organic matter
- Cream
- Milk
- Latex paints
- Foam rubber
- Gelatin
- Fog
- Smoke
- Montmorillonite and other silicate clays
- Bovine cartilage
- Albumin derivatives
- Dextrans
- Hydroethyl starches
- Bone tissue
- Smog
- Detergents
- Silica gel
- Titanium oxide
- Ruby
