Emulsions-Microemulsions-Lyotropic Liquid Crystals

One of the most important aspects of surface and colloid chemistry is the subject of oil-water emulsion technology. Oil is sparingly soluble in water, and vice versa. Science of emulsion is also important since many biological systems use the same principles, such as milk. The essential subject of emulsion is based on the fact that oil and water do not mix if shaken. 

As is well known, if one shakes oil and water, oil breaks up into small drops (about few mm diameters) but these drops join together rather quickly to return to their original state (as shown here). 

Step I Oil phase and water phase Step H Mixing 

Step III Oil drops in water phase Step IV After short time 

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The expression single phase means that all observable properties are independent from the macroscopic locus of the sampling point. By using this definition, micellar solutions, microemulsions, lyotropic liquid crystals or colloids covered by surfactants are single-phase fluids, while emulsions, i.e. microphase... 

Ionic Liquids can be mixed with surfactants and other solvents to give all types of association colloids that are known with water and other surfactants [28]. Microemulsions can be made as well as different types of lyotropic liquid crystals and emulsions. The Ionic Liquids can play the role of the polar (pseudo-) phase, the apolar one, or of the surfactant. Even two of the three components can be Ionic Liquids. Possible advantages are in the wide temperature range over which such systems show a reasonable stability and the low vapor pressure. Further advantages are the reduced viscosity compared to pure Ionic Liquids (in the cases where the ILs are the inner phase) and the possibility to work in water-free systems [29-31]. 

Microemulsions are microstructured mixtures of oil, water, emulsifiers, and other substances. Since their structures differ in many ways from that of ordinary emulsions, it will be described separately. Liquid crystals (LC) are substances that exhibit special melting characteristics. Further, some surfactant-water-cosurfactant mixtures may also exhibit LC (lyotropic crystal) properties. 

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