**1. Introduction**

In this chapter we will be briefing about the emulsion and its types. We will also be discussing in detail about nanoemulsions, its types, fabrication, application and its properties.

#### **1.1 Emulsion systems and its types**

An emulsion system generally consists of two or more liquids that are immiscible. They are a type of colloids, which are two-phase systems of matter. In emulsion systems, the two phases are dispersed and continuous. One liquid is dispersed (the disperse phase) in the other (the continuous). The different types of emulsion systems can include: oil-in-water (o/w), water-in-oil (w/o), and oil-in-oil (o/o) [1]. The oil-in-oil phase can be polar oil dispersed in non-polar oil, or vice versa. An emulsifier is usually used to disperse immiscible liquids. The emulsifier also plays an important role in the formation and long-term stability of the emulsions. Emulsions can also be classified on the type of emulsifier or the structure of the system. Emulsions being liquids do not have any static internal structure. The droplets are assumed to be statistically distributed in the liquid matrix. According to IUPAC, in emulsions the droplets can be amorphous, liquid-crystalline, or any mixture. The droplet diameters in the dispersed phase range between 10 nm and 100 μm (which may exceed the size limits for colloidal particles) [2]. Some common example of emulsion systems are homogenized milk, some cutting fluids for metal working, egg yolk is an emulsion with the emulsifying agent lecithin, butter is an emulsion of water in fat, and an emulsion of silver halide in gelatin is used as a coating in the photosensitive side of a photographic film [3].

Emulsion system can be classified based on their droplet size as macroemulsion, nanoemulsion, and miniemulsion (**Table 1**).

Emulsion systems find a wide range of applications in the field of food, cosmetics, agriculture, pharmaceuticals (preparation of drugs and drug delivery).
