Definition, Classification of Emulsion and Emulsifying Agents

Emulsion

Definition

Emulsions are biphasic liquid dosage forms that are separated into two components. When two or more liquids are emulsified as droplets, they become miscible when together, but the dispersion is accomplished with emulsifying agents.

The term Emulsion is used in chemistry to refer to a mixture of two or more liquids in which droplets of microscopic or ultramicroscopic size are distributed throughout one of the liquids.

Oil and water are emulsified when mixed with an emulsifier, for instance, a protein, phospholipid, or nanoparticle, which can bind to immiscible liquids. Water-in-oil (W/O) emulsions are dispersed phases consisting of oil and continuous phases consisting of water, or oil in water (O/W) emulsions, which have reversed dispersion and continuous phases. What type of emulsion is created depends on what emulsifier was used. Water- and fat-soluble surfactants are classified as hydrophilic or lipophilic based on their moisture capacity. Hydrophilic surfactants dissolve in water and act as emulsifying agents for O/W whereas lipophilic (or hydrophobic) surfactants dissolve in the oil and act as emulsifying agents for W/O.

In an emulsion, you have two phases. On the one hand, there is the dispersed phase while on the other hand, there is the continuous phase.

Examples - Emulsions are substances that contain fats and liquids. Milk has fat in it, Butter has oil in it, Liquid paraffin has paraffin in it, etc.

Classification

Emulsions can be classified into three categories:
1. Simple emulsions
O/W Emulsion of Oil in Water
W/O emulsion of water in oil 

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

3. Microemulsions
Water-in-Oil Micro Emulsions
Oil-in-Water Micro Emulsions

What separates oil in water emulsions (O/W) from water in oil emulsions (W/O):

O/W emulsion (O/W)	Emulsion of water in oil (W/O)
Emulsions of O/W are continuous emulsions whereas emulsions of oil and water are dispersed emulsions	Emulsions of O/W are continuous emulsions whereas emulsions of oil and water are dispersed emulsions
Easily washable from the skin due to its lower viscosity	Viscose, which cannot be washed from the skin easily with water and is more viscous than oil
Vanishing cream can also be the example	Cold cream can be an example

Multiple emulsion - Emulsions consisting of more than one phase: A dispersed phase containing small droplets of the continuous phase is found in emulsions consisting of more than one phase. 

Uses of emulsions

Pharmaceutical applications: It is used for pharmaceutical purposes because it has an excellent bioavailability and absorption rate. Primarily, it is used as a component of topical products such as creams, lotions, etc.

Cosmetic industry: A large number of cosmetic products use emulsion. Examples: creams, lotions, and hair conditioners.

Food industry: Emulsions are used in some food products, such as milk, peanut butter, ice cream, and so on. Emulsions are easily understood in this industry due to their application.

Paint industry: Emulsion paints and inks are examples of the paint industry.

Fire extinguisher: Thixotropic high internal phase ratio emulsions cannot be ignited. The product is ideal for extinguishing fires.

Advantages

• Make sure the unpleasant taste is covered up.
• Bioavailability should be increased.
• The third type of medication is sustained release.
• The cost of the solution is very reasonable

Disadvantages

• Creating and sedimentation are problems
• difficulty in handling
• Phase inversion

Emulsifying agents

Definition

Using an emulsifier, or surface-active substance, an emulsion can be made that's both fat-soluble and water-soluble. To disperse uniformly in the continuous phase, this method helps disperse the dispersed phase.

Emulsifying agents (Emulsifier) examples include:

Emulsifying agents derived from natural sources: Acacia, Tragacanth, etc.

We use synthetic emulsifiers such as Polysorbate 20, Polysorbate 80, sodium lauryl sulfate (SLS), and Sorbitanlaurate, etc.

Classification

1. Emulsifiers made from natural ingredients:

• Animal sources- Wool fat, Gelatine, etc.
• Vegetable sources- Agar, Tragacanth, Gum acacia, etc.

2. Emulsifying agents that are semi-synthetic: For example, methylcellulose and sodium carboxymethyl cellulose.
3. Emulsifying agents derived from synthetic materials are:

• Inorganic emulsifying agents: Milk of magnesia
• Cationic emulsifying agents: Benzalkonium Chloride
• Anionic emulsifying agents: Sodium lauryl sulfate (SLS)
• Non-ionic emulsifying agents: Glyceryl ester

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