Products
Many pharmaceuticals, cosmetics (personal care products), medical devices, and foods (e.g., milk, mayonnaise) are emulsions.
Structure and properties
Emulsions are liquid or semi-solid preparations for external or internal use. They are dispersed systems (dispersions) in which two or more liquid or semisolid phases are combined by emulsifiers, resulting in a mixture that is heterogeneous at the microscopic level. An emulsion consists of micrometer-sized droplets, which constitute the disperse (inner) phase, and the outer (continuous, closed) phase. It is usually produced under agitation, for example by stirring or shaking. In the narrower sense, only mixtures of liquids are called emulsions. Hydrophilic phases (such as water and aqueous solutions) and lipophilic phases (such as fatty oils or hydrocarbons) are not miscible. Phase separation occurs, with the fat floating on top. They can be combined with the aid of an emulsifier, which is amphiphilic, i.e. it has both a hydrophilic and a lipophilic character. Simple emulsifiers are the salts of fatty acids, which are formed when fatty oils or fats are saponified with a base such as sodium hydroxide or potassium hydroxide. There are numerous other representatives, for example sodium lauryl sulfate, gelatine, the polysorbates and lecithin. Depending on which phase is on the outside and which is on the inside, one speaks of an oil-in-water emulsion (O/W) or a water-in-oil emulsion (W/O). Furthermore, there are also so-called multiple emulsions, e.g. W/O/W and O/W/O. The emulsifiers are designated accordingly. Emulsions intended for ingestion are usually O/W emulsions. This masks the taste of the oil. Emulsions can also be used to increase oral absorption and thus bioavailability. Because of the water content of the emulsion, a preservative is usually needed. This is because water is susceptible to microbial contamination.
Areas of application
Emulsions are widely used in pharmaceuticals, especially for the preparation of semisolid drugs, e.g., for creams and lotions with or without active pharmaceutical ingredients. There are also emulsions, which are intended for ingestion and injection and infusion emulsions, for example for parenteral nutrition.
Adverse effects
Due to their heterogeneous nature, emulsions become unstable and fall apart over time or due to external influences. This can manifest itself, for example, in phase separation, flocculation, creaming, or sedimentation. As a result, the preparation loses its desirable properties.