An emulsion is a colloidal system consisting of at least two immiscible liquids, where one phase is dispersed in the other in the form of droplets.

Emulsifiers are chemical compounds of amphiphilic structure, which means that hydrophilic polar groups (called ‘head’) and hydrophobic non-polar groups (called ‘tail’) are present in their structure. The most common emulsifiers are surfactants. The emulsifier molecules adsorb at the phase boundary, reducing the interfacial tension. After reducing the tension, a spontaneous emulsification process takes place under the influence of the movement of particles. The resulting stable system is called an emulsion.

Two basic types of emulsions are distinguished:

• oil in water (O/W) – formed as a result of dispersion of a non-polar oil phase droplet in the polar aqueous phase; in this system water is a continuous phase and oil is a dispersed phase,
• water in oil (W/O) – formed as a result of water dispersion in the oil phase, where the water layer is a dispersed phase and the oil is a continuous phase.

There are two methods for obtaining emulsions:

• mechanical shaking of immiscible liquids – using shakers or mixers,
• the use of ultrasound – using an ultrasonic field with thousands of vibrations per second.

Emulsifiers are used in almost all branches of industry. Among others, they are used in the production of agrochemicals, detergents, paints, varnishes, food products, packaging, cosmetics; cleaning and industrial washing; in the construction, paper, metallurgy, pharmaceutical, fuel and textile industries.