An emulsion is a dispersion of finely divided liquid droplets in another liquid. These are liquid-liquid colloidal systems, however, the two liquids are immiscible. In most cases, one of the two liquids is water and the other is oil since it is immiscible in water.
If the liquids that are mixed have very little or no mutual solubility, emulsions can be formed spontaneously or, more frequently, mechanically via agitation. Emulsions are stabilized by substances that either create films on the droplet’s surface, like soap molecules, or give them mechanical stability like colloidal carbon.
An emulsion is defined as a liquid-liquid colloidal system that is formed by combining two or more immiscible liquids. The process of mixing liquid to form an emulsion is called emulsification.
Examples of Emulsions
Butter, milk, Egg yold, cold cream, hair cream, etc. are some examples of emulsions.
Types of Emulsion
Emulsions are of two types:
- Oil-in-Water type (O/W type): Here, water serves as the dispersion medium while oil serves as the dispersed phase. An example of this type is milk, which contains liquid fats that are dispersed in water.
- Water-in-Oil type (W/O type): Here, the dispersion medium is oil and the dispersed phase is water. Butter and cold cream are examples of it.
Properties of Emulsion
- Dilution: With any quantity of the dispersion medium, emulsions can be diluted. The dispersed liquid, on the other hand, will instantly create a separate layer when combined with it. This property of emulsions is used to detect the type of a given emulsion.
- Demulsification: Emulsions can be “demulsified”—broken into their component liquids—by heating, centrifuging, freezing, or by adding significant amounts of electrolytes. By eliminating the emulsifying agent, they are also broken. A strong acid, for instance, can be added to break up an oil-water emulsion that has been stabilized by soap. Acid changes soap into soluble free fatty acids that cannot be dissolved.
Preparation of Emulsion
Emulsification is the process of dispersing a liquid in the form of an emulsion. Agitating a small part of one liquid with the majority of the other can accomplish this. The process is improved by homogenizing a mixture of the two liquids using a colloid mill.
Simply shaking the two liquids produces unstable emulsions. The dispersed phase’s droplets condense to form a distinct layer. During preparation, a tiny amount of a third material known as the emulsifier or emulsifying agent is introduced in order to create a stable emulsion. Typically, this takes the form of a hydrophilic colloid, synthetic detergent, or soap.
Role of Emulsifier / Emulsifying agent
As one liquid rolls into droplets, the emulsifier concentrates at the interface and lowers surface tension on that side. For instance, soap is composed of a water soluble polar head (COO–Na+) and a lengthy hydrocarbon tail (oil soluble) . In an O/W type emulsion, the head extends into the water while the tail is attached into the oil droplet. As a result, the soap acts as a barrier and prevents the emulsified droplets from coalescing.
Application of Emulsion
Some of the major applications of emulsion are:
- The formation of an oil-in-water type emulsion is the basis for the cleansing activity of soap and synthetic detergents for washing clothes, bathing, etc.
- In the intestine, emulsification is used to break down fats.
- An emulsion of fat and water is milk. Butter and milk cream are examples of emulsions.
- Various body lotions, vanishing creams, cold creams, and other products are all emulsions.
- To facilitate absorption in the body, a number of oily drugs are produced in the form of emulsions.
- Arun Bahl, B. S. Bahl & G. D. Tuli, Essentials of Physical Chemistry, S. Chand and Company Ltd., New Delhi, 2012.
- Principles of colloid and surface chemistry, Paul C. Hiemenz and Raj Rajagopalan
- Introduction to Applied Colloid and Surface Chemistry; Georgios M. Kontogeorgis, Søren Kiil.