Emulsions – Definition, Types, Preparation, Properties

Did you know that “emulsion” comes from the Latin word “mulgeo,” which meaning “to milk”? Milk is a fat-water emulsion containing a variety of additional ingredients. But what precisely are Emulsions, and what role do they play in our daily lives and in the workplace?

Emulsions are combinations of two or more types of liquids, one of which is a droplet of microscopic or even nanoscale size that is spread throughout the other. These are often made from liquid components in their natural state or, more commonly, through methods such as agitation, assuming that the fluids being mixed do not have any mutual solubility. Let take a closer look at each of them individually.

Emulsions

“Colloidal solutions in which both the dispersed phase and the dispersion medium are liquids are known as emulsions.”

Milk, which has fat globules scattered in the water, is a nice example of an emulsion. Emulsified globules are about 10^-6m in size. In some ways, emulsions are similar to lyophobic sols.

A set of mixed systems known as solutions, gels, or suspensions are also referred to as emulsions. Consider the photographic emulsion, which is a gelatin gel with microscopic crystals distributed throughout. Other types of emulsions include butter, which is a water-in-fat emulsion, and egg yolks with lecithin.

Types of Emulsions

Emulsions are characterized as follows based on the nature of the dispersed phase:

1. Oil-in-water Emulsions (O/W): An oil-in-water emulsion is one in which oil serves as the dispersed phase and water serves as the dispersion medium. A good example of an oil-in-water emulsion is milk. Liquid fat globules in milk are distributed in the water. Other examples are disappearing cream and so on.
2. Water-in-oil Emulsions(W/O): A water-in-oil emulsion is one in which water serves as the dispersed phase and oil serves as the dispersion medium. Oil emulsions are another name for these emulsions. Emulsions such as butter and cold cream are common examples. Other examples are cod liver oil and so on.

Preparation of Emulsion

Emulsions are made by vigorously churning a mixture of the necessary oil and water with a high-speed mixer or ultrasonic vibrators. Simple mechanical stirring results in unstable emulsions. Oil and water have a tendency to separate. A suitable stabilizing agent is usually added to achieve a stable emulsion. An emulsifier or emulsifying agent is the name of the stabilizing ingredient. In the beginning, the emulsifier is combined with the oil and water.

Soaps, detergents, long-chain sulphonic acid, and lyophilic colloids such as gelatin, albumin, and casein are examples of compounds that can operate as emulsifiers.

Nature of Emulsion

In the event of a certain emulsion, different emulsifiers may behave differently.

For Example :

• Preparing oil-in-water emulsions requires sodium oleate.
• Water-in-oil is made with magnesium and calcium oleates. When calcium oleate is introduced to a sodium oleate-stabilized emulsion, the system’s stability suffers. The oil-in-water emulsion becomes unstable at a specific ratio of Na⁺, Ca⁺. If the concentration of Ca²⁺ ions is rapidly raised, the emulsion type is reversed, and the oil-in-water emulsion becomes a water-in-oil emulsion.

Identification of Emulsion

There are several methods for determining if an emulsion is an oil-in-water or a water-in-oil emulsion. The following are the characteristics of an emulsion.

1. Dye test: The emulsion is shaken with an oil-soluble colour. It is an oil-in-water type emulsion if colour is visible while gazing at a drop of the emulsion. A water-in-oil type is one in which the entire background is coloured.
2. Dilution test: To the emulsion, add water. If the emulsion can be diluted with water, water serves as the dispersion medium, and the emulsion is an oil-in-water emulsion. If the oil isn’t diluted, it functions as a dispersion medium, and the result is a water-in-oil emulsion.
3. Conductivity test: Add a small amount of an electrolyte (Example: KCl) to the emulsion. If this makes the emulsion electrically conducting, then water is the dispersion medium. If water is not in the dispersed phase.

Relationship Between Concentration and Appearance

The interface is a border that exists between the dispersed and continuous phases. Because the phase interphases present in the emulsion scatter light at different wavelengths, the emulsions have a hazy look.

The emulsion’s colour is determined by its concentration. When all light is distributed evenly, emulsions appear white. Low-wavelength light is dispersed more in dilute emulsions, causing the emulsion to look blue in colour. The “Tyndall Effect” is the name given to this phenomenon. The colour will be warped to substantially longer wavelengths and seem more yellow if the emulsion is concentrated enough.

The system appears translucent in colour when particular kinds of emulsions, such as nano-emulsions and micro-emulsions, are used. This attribute arises from the fact that light waves are only scattered by droplets whose diameters exceed one-quarter of the wavelength of the incident light. These systems have a translucent appearance because the particle size is less than 100 nm.

Properties of Emulsion 

• Emulsions exhibit all of the properties of a colloidal solution, including Brownian movement, Tyndall effect, and electrophoresis.
• The addition of electrolytes containing polyvalent metal ions coagulates the globules, demonstrating their negative charge.
• In emulsions, the size of the dispersed particles is bigger than in sols. It has a range of 1000 to 10,000 Ă. The size, on the other hand, is less than that of particles in suspensions.
• By heating, centrifuging, freezing, and other means, emulsions can be separated into two liquids. Demulsification is the term for this procedure.

Emulsifier / Emulsifying agent

To comprehend this, we must first comprehend the merging process. Coalescing occurs when identical particles in an emulsion join together to produce larger, bulkier particles, causing the dispersed phase and dispersion medium to separate.

Emulsifiers act as a physical barrier between the dispersed phase and the dispersion medium, preventing coalescence. Emulsifiers, like soap, have both a hydrophilic and a hydrophobic end, as we’ve seen. As a result, they can cling to both polar and non-polar materials. Consider sodium stearate as an example.

C₁₇H₃₅COO-Na can be represented as:

When added to an o/w emulsion, C₁₇H₃₅COO– molecules surround the oil droplet, with their non-polar tails/hydrophobic end (the hydrocarbon chain) extending into the oil and their polar heads/hydrophilic end (the carboxylate ion) facing the water, as seen in the picture.

The oil (dispersed phase) and water have a stronger adhesive force as a result of this arrangement (dispersion medium). This newly developed adhesive force will be greater than the cohesive force between oil and oil, as well as the cohesive force between water and water. As a result, oil particles will be less likely to clump together to produce larger particles. This helps to keep the emulsion stable by preventing coalescence.

These are compounds that are added to emulsions for the aim of stabilization. The following are the many features of emulsifiers:

• They are compounds that have both a hydrophilic (polar) and a hydrophobic (non-polar) end (non-polar).
• Both water and oil are soluble in them.
• Emulsifiers produce a layer between the dispersed phase and the dispersion medium, preventing the dispersed phase particles from clumping together and separating out.
• Emulsifiers come in a variety of forms, including cationic, anionic, and non-polar.
• The ratio of water and oil in an emulsion determines whether it is an oil-in-water or a water-in-oil emulsion. On the other hand, it is dependent on which of the two liquids can emulsify the emulsifier to a greater amount.
• If the emulsifier is more water-soluble, the water serves as the dispersion medium, while the oil serves as the dispersed phase, resulting in an oil in water emulsion.
• If the emulsifier is more soluble in oil, the oil serves as the dispersion medium, while the water serves as the dispersed phase.

Emulsification Theories

There are multiple theories that accompany the process of emulsification because it involves several processes and mechanisms (both chemical and physical).

• Surface tension theory: This theory defines emulsification as a process that occurs when the interfacial tension between two phases is reduced.
• Repulsion theory: The emulsifying agent generates a film over one phase, which leads to the production of globules, according to this idea. The repulsive force that exists between these chemicals helps them stay suspended in the dispersion medium.

Applications of Emulsions

• Ore concentration in metallurgy
• In the field of medicine
• Soap’s cleaning action
• Emulsification is used to digest lipids in the colon.
• Milk is a fat-in-water emulsion that is an important part of our nutrition.

Sample Questions 

Question 1: Define Emulsion.

Answer :

“Colloidal solutions in which both the dispersed phase and the dispersion medium are liquids are known as emulsions.”

Question 2: Explain the properties of emulsions.

Answer :

Properties of Emulsion

• Emulsions exhibit all of the properties of a colloidal solution, including Brownian movement, Tyndall effect, and electrophoresis.
• The addition of electrolytes containing polyvalent metal ions coagulates the globules, demonstrating their negative charge.
• In emulsions, the size of the dispersed particles is bigger than in sols. It has a range of 1000 to 10,000 Ă. The size, on the other hand, is less than that of particles in suspensions.
• By heating, centrifuging, freezing, and other means, emulsions can be separated into two liquids. Demulsification is the term for this procedure.

Question 3: Explain how to reduce sedimentation and creaming in emulsions.

Answer :

Sedimentation is the downward movement of particles, whereas creaming is the upward movement of dispersed droplets relative to the continuous phase. The factors that impact creaming rate are comparable to those that determine sedimentation rate. Stokes’ law states that

v = (d(ρ-ρ₀)g) / 18η₀

Question 4: Explain emulsifying agent.

Answer :

These are compounds that are added to emulsions for the aim of stabilization. The following are the many features of emulsifiers:

• They are compounds that have both a hydrophilic (polar) and a hydrophobic (non-polar) end (non-polar).
• Both water and oil are soluble in them.
• Emulsifiers produce a layer between the dispersed phase and the dispersion medium, preventing the dispersed phase particles from clumping together and separating out.
• Emulsifiers come in a variety of forms, including cationic, anionic, and non-polar.
• The ratio of water and oil in an emulsion determines whether it is an oil-in-water or a water-in-oil emulsion. On the other hand, it is dependent on which of the two liquids can emulsify the emulsifier to a greater amount.
• If the emulsifier is more water soluble, the water serves as the dispersion medium, while the oil serves as the dispersed phase, resulting in an oil in water emulsion.
• If the emulsifier is more soluble in oil, the oil serves as the dispersion medium, while the water serves as the dispersed phase.

Question 5: How to prepare Emulsion.

Answer :

Emulsions are made by vigorously churning a mixture of the necessary oil and water with a high-speed mixer or ultrasonic vibrators. Simple mechanical stirring results in unstable emulsions. Oil and water have a tendency to separate. A suitable stabilizing agent is usually added to achieve a stable emulsion. Emulsifier or emulsifying agent is the name of the stabilizing ingredient. In the beginning, the emulsifier is combined with the oil and water.

Soaps, detergents, long-chain sulphonic acid, and lyophilic colloids such as gelatin, albumin, and casein are examples of compounds that can operate as emulsifiers.