People often encounter emulsions in everyday life, sometimes without even suspecting that it is they. What are these substances, what are they?
An emulsion is a homogeneous dispersion system of two immiscible liquids. Outwardly, it is practically no different from just a homogeneous liquid. The difference between the emulsion and the latter is the presence of microscopic droplets of the dispersion phase, distributed in the main liquid, i.e. dispersion medium. The simplest example of such a system, which everyone has encountered in everyday life, is milk. In it, milk fat is dispersed in water.
Types of emulsions
The main factors affecting the ratio of the emulsion to a particular type are:
- composition of liquid phases
- ratio between liquid phases
- emulsification method
- the nature of the emulsifier
- other factors
In accordance with these points, the following types of emulsions are distinguished:
Straight. They are formed from a non-polar liquid dispersed in a polar medium, usually oil-in-water. The best emulsifiers for direct emulsions are potassium and sodium salts of fatty acids, i.e. soaps, which, being adsorbed on the surface of drops, reduce surface tension, increase mechanical strength, and protect against destruction.
Reverse (invert) emulsions. These emulsions include water-in-oil systems. Emulsifiers - insoluble salts of fatty acids, for example, calcium, aluminum, magnesium.
Lyophilic. These emulsions are capable of spontaneous formation, as they are thermodynamically stable. Formed near the critical mixing temperatures of the two phases. An example of such an emulsion is a cutting fluid.
Lyophobic. These emulsions do not form on their own, since they do not have thermodynamic stability. Mechanical influences or the process of the formation of drops of one of the phases from a supersaturated solution are the main pathways for the formation of lyophobic emulsions.
Methods for producing emulsions
There are two ways to obtain emulsions: droplet crushing, film formation and rupture.
Crushing drops. The dispersion phase is slowly added to the dispersion medium in the presence of an emulsifier with stirring. As a result, many small droplets are formed. The number of drops and their size depends on the nature of the emulsifier, stirring speed, temperature, pH of the medium, and the rate of introduction of the dispersion phase.
Film formation and rupture. A liquid that does not mix with the dispersion medium forms a film on its surface, which is burst by air bubbles coming out of a special tube at the bottom of the vessel. In this case, intensive mixing and emulsification occurs. A similar mechanism of action, but more effective, is the use of ultrasound for the formation and mixing of the emulsion.