Colloids are heterogeneous systems composed of particles (distributed phase) broken down into microscopic particles (dispersion medium). Colloidal particles have a significant surface area/unit mass due to their small size. Their scattered phase is larger than genuine solutions but a lower size than suspension. As a result, they have distinct properties.

The Physical State’s Dispersion Medium And Dispersed Phase

A colloidal system is a complex homogeneous particle in which particles are distributed uniformly throughout the fluid and it depends on the dispersion medium and dispersed phase’s state: solids, liquids, or gases. 

There are eight different types/states of colloidal systems. We can divide colloids into eight groups based on the phase of the dispersion medium and the dispersed phase:

• Aerosol
• Solid Aerosol 
• Sol
• Emulsion
• Foam
• Solid foam
• Gel
• The Solid Sol

Classification of Colloidal Systems 

Colloidal systems are classified into the following categories:

Lyophobic colloids

• Lyophobic colloids don’t like the solvents (Lyo means solvent, and phobic means hating). Therefore, the dispersed phase particles have little or no affinity for the dispersion medium. 
• For example, metals and sulphides simply mix with the dispersion medium and do not create colloids. This form of colloid necessitates unique processes for preparation and stabilisation to be preserved, and the mixing is irreversible. The mixture cannot be returned to its original state after precipitating it. Thermodynamically, a lyophobic sol is unstable. 
• The existence of electrical charges on the surfaces of the particles is the sole factor that keeps them stable. A modest amount of electrolyte added to a lyophobic sol stabilises the system by charging the particles. Colloidal sols of gold, silver, Fe(OH)3, As2S3, and other metals are examples of lyophobic colloids.

Lyophilic colloids

• Lyophilic colloids were solvent-friendly (Lyo means solvent and philic means loving).
• Colloidal solutions are those in which the dispersed phase particles have a strong affinity for the dispersion medium.
• These are generated immediately by substances such as gum, gelatine rubber, and so on when they are mixed with a suitable liquid (the dispersion medium).
• Gels are frequently generated by cooling lyophilic sols with big linear molecules and a significantly higher viscosity than the solvent.
• Lyophilic sol is simply created by combining a colloid with a liquid solvent.
• Stability is achieved primarily by applying an electric charge to the dispersed particles and surrounding each particle with a protective solvent sheath that inhibits mutual adhesion when the particles collide due to Brownian movement.
• Similarly, adding a small quantity of an electrolyte to a lyophilic colloid in a considerable amount does not result in coagulation.

Amphiphiles

Amphiphiles, also known as related colloids, are surface-active agents with a hydrophilic head and a lipophilic tail. Amphiphiles exist clearly and in a sub-colloidal size range when present in a liquid at low concentrations. 

Multimolecular colloid

Multimolecular colloids are made up of numerous atoms or tiny molecules (diameter 1 nm). These colloids are typically lyophobic. As an example, consider gold and sulphur sols. 

Weak Van der Waal interactions hold small molecules (or atoms) together. Therefore, these colloids are typically lyophobic. This implies that these colloids have little or no attraction forces with the dispersion medium.

Macromolecular colloid

The molecules in macromolecular colloids have sizes and dimensions similar to colloidal particles (100 nm). Proteins, starch, and cellulose are a few examples of colloids that are comparable to actual solutions:

• Aerosol is a solid or liquid that is dispersed in a gas.

• Emulsion is a liquid-in-liquid phase.
• Foam is a gas that disperses in a liquid (or solid).
• Gel is made up of two interpenetrating networks, and it’s difficult to tell which is dispersed and which is continuous.

The Types of Dispersed Phases

Dispersible particles of multimolecular colloids are held together by Van der Waals forces. As an example, consider gold sol, sulphur sol, and so on.

A gold sol may have particles of varying sizes of multiple gold atoms. Sulphur sol, for example, is made up of particles that have a lot of S8 molecules.

Colloids with Macromolecular Structure

The dispersed phase particles in this colloid are large enough to have a colloidal dimension. These molecules are known as macromolecules because they have an extremely high molecular mass. Colloidal solutions generated when such compounds are dispersed amidst the best suitable dispersion media are macromolecular colloids.

The majority of lyophilic sols are macromolecular colloids.

Natural macromolecules include starch, proteins, gelatin, cellulose, nucleic acids, etc. Synthetic polymers, such as polyethene and synthetic rubber, are examples of created macromolecular colloids.

Associated Colloids

Some compounds act as colloids at high concentrations due to aggregation formation. At low concentrations, however, they operate like regular strong electrolytes. Moreover, the micelles are the aggregates that form due to this process, and such colloids are referred to as linked colloids.

Colloids’ Applications

A colloid is used to thicken industrial items such as toothpaste, lotions, lubricants,  coatings, etc. In addition, colloids are important in the production of paints and inks. For example, the ink used in ballpoint pens is a gel (liquid-solid colloid).

Here are a few more examples:

• Smoke electrical precipitation
• Drinking water purification 
• Medicines
• Tanning
• Soap and detergent cleaning action
• Films and photographic plates
• Industrial products from the rubber industry

Conclusion

In this article, we have investigated the colloids classification system, which consists of eight varieties of colloids based on dispersion phase and dispersion medium. The definitions and examples of lyophilic colloid, lyophobic colloid, macromolecular colloid, multimolecular colloid, and allied colloids were examined.