What is Emulsion?

There are various mixtures in Chemistry made by combining different substances having different or similar mediums. An emulsion is an important type of colloid used for various purposes in daily life. A lot of emulsions used are man-made and created to perform specific functions. Furthermore, emulsions are also used in manufacturing processes in industries.

Emulsion

A colloid of two immiscible liquids in which one fluid contains a dispersion of the other fluid is known as an emulsion. To put it in another way, an emulsion is a unique type of mixture made by mixing liquids that normally do not mix. The word emulsion is derived from the Latin word ‘emulsus’, which means ‘to milk’. Emulsification is the process that turns mixtures into an emulsion.

Sometimes, the word colloid and emulsions are used together; however, it is important to note that for an emulsion both the combining agents are in the liquid phase while for a colloid the combining agent can be of any medium. Hence, not every colloid is an emulsion but every emulsion can be categorised as a colloid.

Types of mixtures

A group of blended systems, such as gels, suspensions or solutions can also be referred to as emulsions. One example is a photographic emulsion, a gelatin gel with tiny crystals dispersed throughout. Other types of emulsions are butter, a water-in-fat emulsion, and lecithin in egg yolks. 

The table below shows the types of mixtures that are formed when a dispersed phase is combined in a dispersed medium :-

Process of emulsification

• When the contact surface tension between two liquids is reduced, emulsification can occur. Surfactants function in this manner.
• An emulsifier can form a film above one phase of a mixture, resulting in blobs that subdue each other and stay distributed evenly or are suspended.
• The viscosity of the medium is increased by certain emulgents, enabling the granules to stay suspended. Acacia, tragacanth hydrocolloids and glycerine are some of the common examples of the emulsification processes.

Theories on emulsification

The process of emulsification can involve a variety of chemical and physical processes.

• Surface tension theory – This theory states that emulsification occurs when the surface tension between two stages is reduced.
• Repulsion theory – The emulsifying agent forms a film over one phase, forming globules that repel each other, according to the repulsion theory. They remain in suspension in the dispersed phase due to this repulsive force.
• Modification of viscosity – Acacia, tragacanth, polyethylene glycol and other emulgents increase the viscosity of the medium, which aids in the creation and maintenance of globule suspension in the dispersed phase.

Emulsifying agent

Emulsifying agents are active ingredients that are used to stabilise the two phases in emulsions. It works at the interface to improve an emulsion’s kinetic stability, ensuring that the amount of the particles does not alter significantly over time, thereby stabilising the emulsion.

Emulsifiers are chemicals with a polar or hydrophilic (water-soluble) part and a non-polar (hydrophobic or lipophilic) part. As a result, emulsifiers have varying degrees of solubility in both water and oil.

Emulsifiers and emulsifying particles, according to the Bancroft rule, actively promote dispersion of the phase, in that they do not dissolve well. Proteins, for example, dissolve best in liquid than in oil, resulting in oil-in-water emulsions.

Applications of emulsion

• Oil-in-water mixtures are widely used in food. Butter, margarine, homogenised milk, mayonnaise and other similar products are examples.
• In the field of healthcare, emulsions are used in many pharmaceutical and cosmetic dosage forms. Emulsions are cosmetics such as moisturisers, creams and biphasic makeup removers. Emulsions are used in many oral and topical dosage forms.
• Vaccines and microbes are delivered using microemulsions. Emulsion formulations include cod liver oil, cortisol and polysporin.
• Emulsions are used in the production of polymer dispersions in chemical synthesis. These include the basic ingredients used in glues and paints.

Conclusion

The emulsion is an important mixture in the field of chemistry which is used in various pharmaceutical and food-processing industries. These mixtures are commonly used in different products. The types of emulsion display the solubility of the different components which can be experimented with and studied in chemistry.