Emulsions – their Characteristics and Types

What is an emulsion?  

An emulsion is a mixture of two immiscible liquids, one being dispersed phase and the other being dispersion medium. Its particle size lies between the true solution and suspension, an emulsion, is a colloidal solution.

To simply put the definition of emulsion, we need to know some of the crucial phrases of emulsion – hydrophobic and hydrophilic. 

Hydrophobic is anything that doesn’t dissolve in water like oil; vice-versa, hydrophilic is anything that easily dissolves in water like sugar, salt, etc.

Colloidal system :  A colloid system is a mixture in which one part is dispersed through another in a constant motion and it is usually formed when both parts do not combine to form a solution, but instead get dispersed through another. 

Disperse phase – the component which is present in small portions and consists of particles of colloidal dimension.  

Dispersion medium –  the medium in which colloidal particles are dispersed is called colloidal medium.

Dispersed medium and the dispersed phase has been categorized into the sol, solid sol, aerosol, emulsion, gel, foam, etc. 

Some examples of emulsions include homogenized milk, biomolecule condensates, vinaigrettes, butter, and some cutting fluids for metalworking. 

 Types of emulsions  

There are two types of emulsions. These types of emulsions can be classified as -O/W type and W/O type.  

• O/W is oil in water emulsion. In oil in water emulsion, oil acts as the dispersed phase, and water acts as the dispersion medium. Mayonnaise and Hollandaise sauce are some examples of oil in water emulsions. 
• W/O is water in oil emulsions. In the water in oil emulsion, water acts as the dispersed phase, and oil acts as the dispersion medium. Butter, cold cream and coated olive oil are some examples of water in oil emulsions.

By simply changing the portion of the dispersed phase and the dispersion medium, these two types of emulsions become interconvertible.  

Distinguish between oil in water and water in oil emulsions

There are a few tests that can be used to distinguish between oil in water and water in oil emulsions:  

• Dye test: Some oil-soluble is added to the emulsion. If the droplets become coloured, then the emulsion is oil in water type, and if the background becomes coloured, then the emulsion is water in oil type. 

1. Conductance measurement: This type of method adds a small amount of electrolyte to the emulsion. Then a change in its electrical conduction is observed. If there is no significant change in conductance, it is water in oil emulsion. But if there is an increase in conductance, then the emulsion is an oil in water.  
2. Dilution test: If the emulsion is possibly separated in a layer by adding water, it indicates that it is water in oil type. But in the case of dilution, adding water then indicates that water is the dispersion medium and the emulsion is oil.    

Theories of emulsions

There is actually more than one theory that proves the process of emulsions as it involves several mechanisms of both chemical and physical science.

• Surface tension theory – Emulsification is defined as a process in which the interfacial tension between two phases is reduced in this theory.
• Repulsion theory – According to the repulsion theory, the emulsifying agent produces a coating over one phase, which causes the production of globules. They stay suspended in the dispersion medium as these chemicals act as opposing elements with each other because of the repulsive force that exists between them.

Characteristics of emulsions

The physical properties of the emulsion results have a different form from either of its two components. For example, emulsions can be made as thick as cream, which does not flow, while water and oil are thin free-flowing liquids. As a result, opaque emulsion-like thick cream can be designed to have a lustrous, pearlized appearance. While water and oil are transparent.  

One of the most characteristic of emulsions is their inherent instability. However, though the dispersed drops are small, gravity obviously exerts a measurable force. Over time, the particles come together to form whole or larger drops, which then tend to rise to the top of the mixture or settle down at the bottom of the mixture. The internal and external phases are thus ultimately separated into their original components due to this process. The separation depends upon how the emulsions are formulated and what kind of physical environment to which it was exposed.  

Emulsions exhibit the tyndall effect, Brownian movement, electrophoresis, etc.

Tyndall effect: when the light is scattered in a colloidal solution by colloidal particles is called the Tyndall Effect.

Brownian movement: the common colloidal particle exhibits zig-zag, criss-cross movement in colloidal solution is called Brownian movement.

Electrophoresis: under the influence of an electric field, the movement of colloidal particles in a colloidal solution is called electrophoresis.

Emulsion and its properties

• Interface in emulsion contains both the dispersed and the continuous within the boundary coming between the phases. 
• Emulsions appear white when light is dispersed in equal proportions.
• Due to various phase interfaces scattering light passing through the emulsions, it can have a cloudy appearance.

Emulsion’s uses

The process of emulsion is employed in industries like tanning and dyeing, as well as the plastics and synthetic rubber manufacturing processes.

What is multiple emulsion?

A complex polydisperse system where oil in water and oil in oil emulsions exist together, stabilized by the lipophilic and hydrophilic elements, respectively, is called a multiple emulsion. The ratio of the water in oil and oil in water is very important to achieve stable multiple emulsions. 

Conclusion

An emulsion is a mixture of two immiscible liquids, one being dispersed phase and the other being dispersion medium. The dispersed phase is when the component is present in small portions and consists of particles of colloidal dimension. The dispersion medium in which colloidal particles are dispersed is called a colloidal medium. There are two types of emulsions – oil in water and water in oil. The physical properties of the emulsion results have a different form from either of its two components. The most important characteristic of emulsion is its inherent instability. Three tests can be done to identify the emulsion –dye test, dilution test, and conductance measurement. The ratio of the water in oil and oil in water is very important to achieve stable multiple emulsions.