Emulsion

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Introduction

Emulsions are mixtures composed of two or more liquids types, where one is like droplets, of tiny or even ultramicroscopic size, distributed throughout each other. Usually, these are formed from the liquid components either in natural form or, more often, using mechanisms such as the agitation, provided that these fluids mixed have no type of mutual solubility.

Emulsions are stated as stabilized by some of the agents forming films at the droplet surfaces or those which impart to them as a kind of mechanical stability. Eventually, the unstable form of emulsions separates into two different forms of liquid layers. The stable emulsions are destroyed either by destroying or by deactivating the emulsifying agent. An emulsifying agent example is, by the addition of suitable third party substances or even by the process of heating or by freezing.

A few of the common emulsions are milk (where the fat molecules or droplets dispersion happens in the aqueous solution) and butter (the dispersion of droplets of particles of an aqueous solution present in the fat).


What Is Emulsion?

An emulsion is a colloid consisting of two or more non-homogeneous liquid types wherein one of such liquids contains the dispersion of the different forms of liquids.


Emulsion Examples

Emulsions consist of a dispersion of two liquids, where each other are immiscible. One of the liquids acts as the dispersion medium, whereas the other will act as the dispersed phase. In other words, emulsions are the colloids in which both the dispersion medium and the dispersed phase are liquids. The oil and water mixtures are the emulsions when they are shaken together. Then, the oil forms drop and disperse throughout the water.

The term emulsion can also be applied to a group of mixed systems, which are called as solutions, or suspensions, or gels. For example, the photographic emulsion type is a gelatin gel consisting of tiny crystals that are dispersed in it. A few other examples of emulsions include butter, egg yolk containing lecithin, and an emulsion of water in fat.

Dispersed Phase

Dispersion Medium

Type of Colloid

Example

Solid

Solid

Solid

Some Coloured Glasses And Gemstones

Solid

Liquid

Solid

Paints, Cell Fluids

Solid

Gas

Aerosol

Smoke, Dust

Liquid

Solid

Gel

Cheese, Butter, Jellies

Liquid

Liquid

Emulsion

Milk, Hair Cream

Liquid

Gas

Aerosol

Fog, Mist, Cloud, Insecticide Sprays

Gas

Solid

Solid

Pumice Stone, Foam Rubber

Gas

Liquid

Foam

Froth, Whipped Cream, Soap Lather


Types Of Emulsion

Based on the properties of the dispersion medium and the dispersed phase, emulsions can be classified into two types. They are given below.

1. Oil in Water (O/W)

In this emulsion type, the oil will be the dispersed phase, whereas the water will be the dispersion medium. The best example of this emulsion type is milk. The fat globules (acts as dispersed phase) contained in the milk are suspended in water (acts as dispersion medium).

2. Water in Oil (W/O)

In this emulsion type, water will be the dispersed phase, whereas oil will be the dispersion medium. Margarine (a spread used for baking, flavouring, and working) is an example of water in the oil emulsion.


Working of Emulsifiers

Before going to understand this, we need to understand the process of coalescing first. Coalescing is the process where similar particles in the emulsions come together to form bulkier and larger particles leading to the separation of the dispersion medium and dispersed phase.

The meaning of Emulsifiers can be defined as it helps in preventing the coalescing by forming as a physical barrier between the dispersed phase and the dispersion medium. As noticed in the previous emulsifiers, such as soap, it has both a hydrophobic end and a hydrophilic end. Hence, they can attach to both polar substances and non-polar substances. If we take the example of sodium stearate, the C17H35COO–Na can be represented as follows.

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When this is added to an Oil in Water emulsion type (O/W), the C17H35COO– molecules surround the oil droplet with their non-polar hydrophobic/tails end (hydrocarbon chain) extending into the oil & their polar hydrophilic/heads end (carboxylate ion) facing the water as given in the below figure.

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This complete arrangement brings a stronger adhesive force between both the oil (dispersed phase) and water (dispersion medium). This newly formed adhesive force will be more compared to the cohesive force between oil - oil and water - water. Thus, the oil particles will not tend to come together to form larger particles. This also helps in preventing the coalescing, thereby stabilizing the emulsion.

Note: For w/o type of emulsion, the orientation of the emulsifier would be the opposite of the o/w emulsion type. i.e. the non-polar (hydrophobic end) tail extends outside, and the polar (hydrophilic end) head faces inwards.


Methods to Identify The Type of Emulsions

  1. Dilution test

On adding water to an o/w emulsion type, still, it will remain stable as the water is the dispersion medium, whereas, on adding oil, it will get destabilised because oil & water are immiscible. Likewise, w/o emulsion type can be diluted with oil & would be stable still, but would get destabilised on the addition of water.

  1. Conductivity test

In this test, the emulsion is kept between the two electrodes, and a bulb is connected in the circuit, as represented in the below diagram. An o/w type of emulsion will conduct electricity as water conducts electricity, but a w/o emulsion will not conduct electricity.

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  1. Dye test

Here, a water-soluble dye is added to the emulsion. If it is an o/w emulsion type, the dispersion medium appears red and the dispersed phase as colourless and vice-versa.


Properties Of Emulsions

  • Emulsions have a cloudy appearance because of the various phase interfaces scattering light passing through the emulsions

  • Emulsions contain both a the dispersed and continuous with the boundary coming between the phases, called “interface”

  • If the emulsion is dilute, then the higher-frequency and low-wavelength type of light will be scattered in more fractions, and this emulsion kind will appear blue. This is also called the Tyndall effect

  • When the light is dispersed in equal proportions, emulsions appear in white colour

FAQ (Frequently Asked Questions)

1. Explain the applications and uses of Emulsion.

Ans: Emulsions are much famous in various science fields. It can be utilized in the dyeing and tanning industries, in the manufacturing process of synthetic rubber and plastics.

  • Micro-emulsions are used to deliver vaccines to kill different microbes

  • Use of emulsion can be applied in cosmetics, personal hygiene, and pharmaceuticals usually

  • It is also used in chemical synthesis mainly in the polymer dispersions manufacturing

  • Nanoemulsions like soybean oil are used to kill microbes

  • It is used in firefighting

  • Mayonnaise, an oil in water emulsion with sodium stearoyl lactylate or egg yolk

2. Explain the Separation of Emulsion and Theories of Emulsification.

Ans: Separation of Emulsions

The various methods where emulsions can be separated into its constituent liquids are listed below.

  • Centrifuging

  • Heating

  • Freezing, and more

Theories of Emulsion or Emulsification

Since there are different mechanisms and processes (chemically and physically) involved in the process of emulsification, there are various theories that accompany it.

  • Repulsion Theory

We learn that the emulsifying agent produces a film over one phase that leads to the formation of globules further with this theory. These compounds also tend to repel each other, and the repulsive force that exists between them helps them to remain suspended in the dispersion medium.

  • Surface Tension Theory

This theory describes or states emulsification as a process that occurs by the reduction of interfacial tension between the two phases.