Emulsifier

The colloidal dispersion of two non-miscible liquids where one liquid acts as the medium of dispersion and the other as a dispersed phase is known as an emulsion. 

In simpler terms, it is a special type of mixture which is prepared by combining two liquids that usually don’t mix. The word emulsion derives from the Latin term “emulgere”, which means to milk as milk is an example of an emulsion of water and fat. Emulsification is the procedure to convert a liquid mixture into an emulsion.

Emulsion Examples 

• Mixtures of water and oil are emulsions when shaken together
• The emulsion of water in fat is butter
• Mayonnaise is an emulsion of oil in water that is stabilised with the help of lecithin in egg yolk
• The cream on top of an espresso

Emulsifiers and Emulsifying agents

An emulsifier is a substance that stabilises an emulsion. 

The following are the various characteristics of emulsifiers: 

• They are both oil and water-soluble
• They consist of both hydrophobic end and hydrophilic end
• We get oil in water emulsion when the emulsifier is more soluble in water, and then the water becomes the dispersion medium, whereas oil becomes the dispersed phase
• When the emulsifier is more soluble in oil rather than water, then oil becomes the medium of dispersion, and water becomes the dispersed phase
• Depending upon the capacity to solvate the emulsifier to a greater extent, it is decided whether the emulsion is an oil-in-water type or water-in-oil type emulsion
• Examples for oil-in-water emulsion include soap, proteins, gum, etc
• Examples of water-in-oil emulsion include long-chain alcohols, heavy metals, etc
• Emulsifiers prevent the dispersed phase and dispersed medium from coming together and forming larger and bulkier particles by forming a layer between both phases
• Emulsifiers can be negatively charged head group, positively charged head group or even uncharged head group

Methods To Identify The Type of Emulsions

We can find out the type of emulsion by the following tests:

• Dilution Test: This test can be conducted by adding water or oil to the emulsion. If water is added, and it gets mixed with the emulsion, then the emulsion is of oil-in-water (o/w) type. If water does not mix with the emulsion, then it is called as water-in-oil (w/o)type. Apart from water, if oil is added to the emulsion and if oil gets mixed up, then it is called water-in-oil type
• Dye Solubility Test: This test can be conducted by adding a water-soluble dye to the emulsion. If the emulsion becomes red, that means it is the oil-in-water type and vice-versa
• Conductivity Test: In this test, some amount of electrolyte is added into the emulsion in order to measure its conductance. If it shows an increase in conductance, then it can be said that the emulsion is of the oil-in-water type. On the other hand, if there is no change in conductance, then it can be concluded that the emulsion is water-in-oil type

Applications of Emulsions

Let us look at the broad applications of emulsions. 

• It is widely used in the pharmaceutical industry to prepare lotions and creams that can be absorbed by the body easily. Several lotions and ointments are emulsions of oil in water and water in oil type
• Properties of emulsions are useful in washing clothes and the whole cleansing actions of soaps are based on it
•  When poured in water, commonly used disinfectants like phenyl work as oil in water type emulsion
• The emulsification process also helps in the digestion process of the human body
• Emulsions are also used in the manufacturing of polymer dispersions
• Emulsifying agents are also commonly used for extinguishing fires
• Emulsions are also used in the manufacturing of vaccines and also widely used in the food industries
• Emulsions like cutting fluid are a type of coolant used in metalworking

 Properties of Emulsions

The following are the properties of emulsions.

• In an emulsion, there is a dispersion medium and dispersed phase
• They show a Cloudy appearance as the light gets scattered between the many phase interfaces when passed through the emulsion
• They exhibit the Tyndall effect. The dilute emulsions with low wavelength light get scattered more in fractions, appearing slightly blue
• By using physical methods such as heating, freezing, centrifuging, emulsions can be broken into their constituent liquids
• Since emulsions are liquid in nature, they do not possess an internal structure that is static
• When dispersed in equal proportions, emulsifiers appear in white colour
• Two liquids can form different types of emulsions, like oil in water emulsion, water in oil emulsion and multiple emulsions like water in oil in water

Mechanism of Emulsification

In the whole procedure of emulsification, several chemical and physical processes and mechanisms are involved. These mechanisms are based on the following theories:

Repulsion Theory

According to this theory, the emulsifying agent makes a film over one stage, which leads to forming globules, and these globules repel each other, and the repulsive force between them forces them to remain suspended in the dispersion medium.

Surface Tension Theory

According to this theory, emulsification is a process that arises by the reduction of interfacial tension between the two mediums.

Conclusion

An emulsion is a mixture that consists of two liquids that don’t mix with each other. They can be categorised into two types, simple and complex emulsions, which can be further divided into oil in water and water into oil types.We can perform three types of tests in order to identify the type of emulsion, namely, conductivity, dye solubility and dilution test. Further, these emulsions come with wide applications such as the preparation of cosmetics, pharmaceutical products, fire retardant materials, and even human digestion.There are several properties of emulsions through which they can be easily identified. These properties include the Tyndall effect, cloudy appearance and white colour when dispersed in equal proportions.