Uses Of Emulsions
Many functional chemical ingredients (such as drugs) are not water soluble and require alcohol or other organic solvents to form solutions. These solvents may be costly, hazardous to handle, or toxic. Emulsions are useful because they allow ways to deliver active materials in water which is inexpensive and innocuous. A related advantage of emulsions is they allow dilution of these active ingredients to an optimal concentration. For example, in hair conditioning products the oils and other conditioning agents employed would leave hair limp and sticky if they were directly applied. Through emulsification, these materials can be diluted to an appropriate level which deposits on hair without negative side effects.
Emulsions are commonly used in many major chemical industries. In the pharmaceutical industry, they are used to make medicines more palatable, to improve effectiveness by controlling dosage of active ingredients, and to provide improved aesthetics for topical drugs such as ointments. Nonionic emulsions are most popular due to their low toxicity, ability to be injected directly into the body, and compatibility with many drug ingredients. Cationic emulsions are also used in certain products due to their antimicrobial properties.
In the agricultural industry, emulsions are used as delivery vehicles for insecticides, fungicides and pesticides. These water insoluble biocides must be applied to crops at very low levels, usually by spraying through mechanical equipment. Emulsion technology allows these chemicals to be effectively diluted and provides improved sprayability. Nonionic emulsions are often used in this regard due to their low foaming properties and lack of interaction with biocidal agents they are carrying.
In cosmetics, emulsions are the delivery vehicle for many hair and skin conditioning agents. Anionic and non-ionic emulsions are used to deliver various oils and waxes which provide moisturization, smoothness and softness to hair and skin. Emulsions formed with cationic emulsifiers are themselves effective conditioning agents since their positive charge is attracted to the negative sites on the hair, thus allowing them to resist rinse off.
Many paints and inks are based on emulsions. Such products may be true liquid-in-liquid emulsions or they may be dispersions. Dispersions are similar to emulsions except that the dispersed phase is usually finely divided solid particles. The same surfactant technology used to formulate emulsions is used to create dispersions of pigments that are used in paints and inks. These dispersions are designed to dry quickly and form waterproof films, while not affecting the color. In this regard emulsions provide benefits over solvent containing systems because of reduced odor and flammability.
Many food products are in the form of emulsions. An example of a naturally occurring food emulsion is milk which contains globules of milk fat (cream) dispersed in water. The whiteness of milk is due to light scattering as it strikes the microscopic fat particles. Salad dressings, gravies and other sauces, whipped dessert toppings, peanut butter, and ice cream are also examples of emulsions of various edible fats and oils. In addition to affecting the physical form of food products, emulsions impact taste because emulsified oils coat the tongue, imparting "mouth-feel." Emulsions are useful tools in industries which directly impact many aspects of society. Although emulsions have been used for years, science still has much to learn. In part, this is due to the infinite number of combinations of emulsion systems and the task of fully characterizing their structure. New emulsion types are constantly being developed as new needs arise; for example a relatively recent advance in emulsion technology is the microemulsion, a special type of emulsion characterized by an extremely small particle size. Microemulsions are completely transparent and have enhanced stability as compared to conventional systems. As science continues to respond to the needs of industry, more unusual emulsion combinations will be developed resulting in improved medicines, cosmetics, pesticides, and dessert toppings.
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Hibbott, H.W., ed. Handbook of Cosmetic Science. New York: Macmillan, 1963.
Lissant, Kenneth J., ed. Emulsions and Emulsion Technology. New York: Marcel Dekker, 1974.
Rosen, Milton J. Surfactants and Interfacial Phenomena. New York: Wiley, 1978.
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