Emulsions - Definition, Types, Emulsifying Agent, Demulsification, Applications, Practice Problems and FAQ

Assume it's a warm, sunny day. Don't we use sunscreen lotion to protect ourselves from the sun's harmful UV rays?

We usually use water-resistant sunscreen so as to protect ourselves even when we sweat.

Water-resistant sunscreens are an oil-in-water emulsion of lubricants, emulsifiers, thickening agents, colouring agents, perfume, UV filters, and absorbers such as zinc oxide.

Milk, vanishing cream, cold cream, and cod liver oil are some of the other common emulsions.

Let’s get to know more about emulsions in this article!

TABLE OF CONTENTS

Emulsions
Types of Emulsions
Working of Emulsifying Agents
Identification of Emulsions
Applications of Emulsions
Practice Problems
Frequently Asked Questions - FAQ

Emulsions

Emulsion is a liquid-liquid colloidal system in which the finely disperses finely divided droplets of one liquid in another. When two immiscible or partially miscible liquids are shaken together, they form a coarse dispersion of one liquid in the other, known as an emulsion.

Preparation of Emulsions

When oil is added to vinegar and shaken, oil in water (O/W) type emulsion is obtained.

It is unstable and sometimes separates into two layers on standing.

Types of Emulsions

1. Oil-in-Water Type Emulsion (O/W Type)

This type of emulsion are formed when oil is the dispersed phase and water is the dispersion medium. Example: Milk, vanishing cream, etc. In milk, fat globules act as the dispersion phase, water as the dispersion medium and casein as the emulsifying agent.

2. Water-in-Oil Type Emulsion (W/O Type)

This type of emulsion are formed when water is the dispersed phase and oil is the dispersion medium. Example: Butter, hair cream, cold cream, etc.

Emulsifying Agents

Generally, emulsions are unstable and they separate into two layers when standing. So, a third component called an emulsifying agent or emulsifier is added for stabilisation. The emulsifiers form an interfacial film between suspended particles and the medium.

Generally, the emulsifiers added in O/W emulsions are gums, proteins, and synthetic and natural soaps; in W/O emulsions, the common emulsifiers added are long-chain alcohols, lamp black, etc.

Emulsification is the process of adding an emulsifier to stabilise an emulsion.

Working of Emulsifying Agents

Emulsifiers or emulsifying agents stabilise the emulsion by reducing the interfacial tension between the liquids forming the emulsion.

The best example to illustrate the working of emulsifiers is soap. Soaps are potassium or sodium salts of fatty acids like sodium stearate (C₁₇H₃₅COONa). Soap molecules consist of two parts namely, the non-polar hydrocarbon part (E.g. C17H35) that is hydrophobic and the polar part (^-COO^- Na⁺) that is hydrophilic.

During the action of soap on oil, the oil drop is surrounded by the soap molecules with the non-polar hydrocarbon part in the oil and the polar hydrophilic part in the water. Subsequently, soap molecules concentrate over the oil drop and form a protective layer. This results in a decrease in the interfacial tension between water and oil and are mixed to form an emulsion.

When the dispersion medium is added in excess, the emulsion is diluted; when the dispersed phase is added in excess, they form a separate layer.

Demulsification

Demulsification is the process of yielding the constituent liquids by breaking an emulsion. Centrifugation, freezing, electrostatic precipitation, heating, or chemical methods that disintegrates the emulsifying agent are some of the methods of demulsification.

Identification of Emulsions

1. Dilution test

When water is added to an O/W emulsion, it stays stable since water is the dispersion medium. On the contrary, when oil is added to an O/W emulsion, the emulsion is destabilised because oil and water are incompatible.

Similarly, when oil is added to an O/W emulsion, the emulsion stays stable, but when water is added, the emulsion is destabilised.

2. Conductivity test

The emulsion is held between two electrodes with an added electrolyte, and a bulb is connected to the circuit as shown in the diagram. An O/W emulsion will transmit electricity in the same way that water does, while a W/O emulsion will not.

3. Dye test

A water-soluble colour is added to the emulsion in this method. The dispersion medium appears coloured while the dispersed phase appears colourless in an O/W emulsion.

Similarly, if an oil-soluble colour is added to a W/O emulsion, the dispersion medium appears coloured while the dispersion phase appears colourless.

Properties of Emulsions

1The properties of emulsions are comparable to the properties of colloids such as Brownian movement, electrophoresis and the Tyndall effect.

Brownian movement is the random movement of microscopic particles in a liquid or gaseous phase caused by collisions with surrounding particles.

Electrophoresis is the movement of charged particles in a fluid when an electric field is applied.

Tyndall effect is the scattering of light by the dispersed particles in the emulsion.

1. The dispersed particles range from 100 Å to 1000 Å in size, which is larger than that of sols.

2. By heating, centrifuging, adding large quantities of electrolytes to precipitate out the dispersed phase or by the chemical destruction of the emulsifying agent, emulsions can be broken to yield the constituent liquids. This process is known as demulsification.

Applications of Emulsions

1. Disinfectants like phenyl and Dettol form emulsions when mixed with water.
2. Emulsion facilitates fat digestion in the small intestine.
3. Emulsion is used in metallurgical processes to concentrate ore using the froth flotation method.
4. The production of emulsions is responsible for soap's cleansing activity.
5. Certain operations such as the building of roads, construction of buildings, etc., use emulsion.

Practice Problems

Q 1. Which type of emulsion is milk?

a. Oil in water
b. Water in oil
c. Both A and B
d. None of the above

Answer: In milk, fat globules act as the dispersed phase and water as the dispersion medium. So, it is an example of oil in water type emulsion.

So, option A) is the correct answer.

Q 2. Which of the processes leads to demulsification?

a. Freezing
b. Heating
c. Centrifugation
d. All of the above

Answer: Demulsification is the process of yielding the constituent liquids by breaking an emulsion. Centrifugation, freezing, electrostatic precipitation, heating, or chemical methods that disintegrates the emulsifying agent are some of the methods of demulsification.

So, option D) is the correct answer.

Q 3. The correct statement about emulsifying agents is:

a. It is added for the stabilisation of two separable layers.
b. It forms an interfacial film between the medium and the suspended particles
c. Both A and B
d. None of the above

Answer: Generally, emulsions are unstable and so they separate into two layers on standing. Therefore, emulsifiers, a third component, is added to stabilise the emulsion. The emulsifier forms an interfacial film between the medium and the suspended particles.

So, option C) is the correct answer.

Q 4. Which of the following is correct when oil is added to an O/W emulsion?

a. O/W emulsion stays stable
b. O/W emulsion gets destabilised
c. It stablises O/W emulsion in the same manner when water is added to the same
d. None of the above

Answer: When oil is added to an O/W emulsion, the emulsion is destabilised because oil and water are incompatible. On the contrary, when water is added to an O/W emulsion, it stays stable since water is the dispersion medium.

So, option B) is the correct answer.

Frequently Asked Questions - FAQ

Q 1. How do emulsions help in building roads?
Answer: Asphalt emulsified in water is leveraged in the entire process of building roads. This helps to reduce the cost of melting asphalt.

Q 2. How does the formation of an emulsion help in the concentration of ores?
Answer: In metallurgical processes, the ore is concentrated by froth floatation by treating the powdered ore with an oil emulsion. The valuable ore particles form, rise to the surface and are skimmed off.

Q 3. Can emulsion droplets be seen with naked eyes?
Answer: Emulsion droplets are larger than sol particles and can be viewed with a conventional microscope or even a magnifying glass.

Q 4. How are emulsifiers removed?
Answer: Emulsifiers are removed by adding a better solvent for them, such as alcohol, phenol, or other demulsifiers.

Related Topics

Preparation of Lyophobic Colloids - Condensation Methods, Dispersion Methods	Adsorption - Important terms, Mechanism of Adsorption
Colloids - Classification (Multimolecular, Associated, Macromolecular Colloids)	Coagulation of Colloids
Properties of Colloids	Colloidal Solutions