COLLOID: CHARACTERISTICS, TYPES, APPLICATIONS, EXAMPLES - CHEMISTRY - 2025

The colloids are mixtures where tiny insoluble particles (called disperse phase) are distributed suspended in a continuous dispersing medium (or fluid phase). The particles of the dispersed phase, like those of the dispersing phase, can be gaseous, liquid or solid in nature.

Examples of colloids include fog, where the dispersing medium is air and the dispersed phase is microscopic water droplets. An obvious case would be a juice, the dispersing medium being the water and the dispersing phase the minerals, vitamins, hydrates, etc.

Clouds are an example of gaseous colloids as they contain microscopic drops or crystals of water suspended in the air. Source: pexels.com

The radius of the dispersed phase particles is between 0.001 µm and 0.1 µm (1nm at 1000 nm). This radius is so small that its sedimentation is very low, which is why colloids are considered stable mixtures; although they tend to have a cloudy appearance.

Colloids have a set of characteristics of their own, such as the Tyndall effect. This consists in that the particles of the dispersed phase are capable of scattering light in all directions.

Colloids, due to their affinity for water, are classified as hydrophilic and hydrophobic. In addition, of these, the following classification exists for them: emulsion, solid emulsion, sol, gel, foam, solid foam, liquid aerosol and solid aerosol.

Characteristics of colloids

Composition

All combinations of gas, liquid and solid can cause colloids; except for gas mixtures that form true solutions. Whether the mixture forms a colloidal dispersion, or suspension, depends on the size of the particles, which can be considered analogous to the solute.

Adsorption

As the colloidal particles are finely divided, it follows that their surface area is very large. This causes the colloidal particles to adsorb ions, as well as gases, liquids and solids.

Electrophoresis

Colloidal particles are usually electrically charged; such is the case of proteins and nucleic acids. Therefore, these macromolecules can move in an electric field, moving towards the anode or the cathode, depending on their electrical charge.

Dialysis

Colloidal particles have a radius that prevents them from passing through the pores of dialysis membranes, allowing them to be separated from other smaller suspended particles. This feature is used to remove undesirable substances in colloidal suspensions.

Brownian movement

Colloidal particles are endowed with random vibratory motion in all directions, that is, Brownian motion. This characteristic contributes to the fact that the particles do not sediment and that the homogeneity and stability of the colloidal suspensions is maintained.

Tyndall effect

Colloidal particles in suspension are capable of scattering light in all directions, a characteristic that solutions do not present. For this reason, the path of a light ray passing through a colloidal suspension can be observed. For example, a beam of light that illuminates the fog.

Types of colloids

Emulsion

It is a colloid formed by the mixture of two immiscible liquids; one forms the dispersed phase and the other the dispersant phase. It is usually the oil-water mixture type.

Solid emulsion

It is a type of colloid in which its dispersed phase is a solid, and its phase or dispersing medium is a liquid.

Foam

It is a type of colloid in which the dispersed phase is a gas that forms bubbles, surrounded by the dispersing phase, which is a liquid.

Beer foam is an example of a foam-type colloid, where the fluid phase is the beer liquid and the dispersed phase is air bubbles. Source: Engin Akyurt via Pexels.

Solid foam

The dispersed phase is a gas and the dispersing phase or medium is a solid. This type of colloid is produced in the making of bread and cheese.

Suns and gels

It is a colloidal system in which the dispersing phase is a solid and the dispersed phase is a liquid in the form of clusters. The condensation or hydrolysis of the sol produces a gel that forms a solid material filled with liquid.

Gels are said to have a density similar to liquids, but their structure resembles that of solids.

Liquid aerosol

It is a type of colloid in which the dispersed phase is a liquid, and the dispersing phase or medium is a gas.

Solid spray

It is a colloidal system in which the dispersed phase is a solid, and the dispersing phase or medium is a gas.

Applications

Biological

Colloids are present in the cells of living beings. In the forms of suns and gels they constitute the cytoplasm and the nucleus. Therefore, life is considered as an expression of the presence of colloids.

Industrial

Colloids are used in paints, plastics, insecticides for agriculture, inks, cements, soaps, lubricants, detergents, adhesives, as well as in many foods.

Paints are made up of colloidal pigments dispersed in liquid solvents, capable of forming a stable solid film as the paint dries.

The ink used in newspaper printing is made of colloidal black carbon in oil. Meanwhile, the ink in the pens is made up of gel-type colloids.

Medicinal

Colloidal solutions are used for plasma volume expansion in patients with postoperative hypovolemia. Silver colloids are used as antibiotics that inactivate enzymes in bacteria, fungi, and viruses. Copper colloids are noted to have anticancer activity. Likewise, mercury colloids have antisiphilitic action.

Colloids are part of drug delivery and transport mechanisms, such as hydrogels, microemulsions, liposomes, micelles, nanoparticles and nanocrystals.

Floors

The main colloidal components of soils are mineral sediments in the form of clay and humus. Soil colloids play an important role in the storage and exchange of minerals required by plants, especially Ca ²⁺, Mg ²⁺ and K ⁺.

Thickening agents

Colloids give the medium desirable flow properties to toothpastes, lotions, lubricants, etc., providing them with stabilization and maintenance of their phases.

Foods

Colloids can be considered to be ubiquitous in foods, as they are present in almost all of them. For example, egg white is a sol-like colloid, which is made up of long-chain protein molecules, tightly wound due to hydrogen bonds.

Heating the egg white breaks the protein bonds and the colloid sol transforms into a hydrogel.

Examples of colloids

Solid emulsion: cheese, butter and jelly.

Emulsion: milk, facial cream and mayonnaise.

Foam: shaving cream, whipped cream and beer foam.

Solid foam: sponge, rubber and pumice stone.

Soles: raw egg white, paint and Chinese ink.

Gels: fried egg white, ballpoint ink and gelatin.

Liquid aerosol: mist, mist, clouds and dew.

Solid aerosol: smoke, automobile exhaust materials, and particulate matter in the air.

References

1. Whitten, Davis, Peck & Stanley. (2008). Chemistry (8th ed.). CENGAGE Learning.
2. Law J., & Brar A. (December 15, 2019). Colloids. Chemistry LibreTexts. Recovered from: chem.libretexts.org
3. Wikipedia. (2020). Colloid. Recovered from: en.wikipedia.org
4. Charles Clay. (April 30, 2018). Characteristics of a Colloid. Sciencing. Recovered from: sciencing.com
5. Cone A. (1995). The use of colloids in clinical practice. British journal of hospital medicine, 54 (4), 155–159.
6. QuimiNet. (February 7, 2013). Colloidal solutions and their uses in medicine. Recovered from: quiminet.com