Emulsion
Emulsion
Emulsions are created by surfactants
An emulsion is a two-phase system that has at least one immiscible liquid (one incapable of being and remaining mixed), called the dispersed phase, distributed in another liquid or solid, called the dispersion medium, in the form of tiny droplets. It is an unstable system, which can be made more stable by the presence of a surfactant. (A surfactant is any soluble substance that reduces the surface tension between two liquids, or one solid and one liquid. A detergent is a common surfactant.) Humans have used emulsions for centuries. They continue to find application in a variety of industries. The word emulsion is from the seventeenth century Latin words emulgere and emulsum, which means to milk.
Emulsions provide a variety of benefits such as the ability to deliver water insoluble active materials from water based products, to improve control over a prod-uct’s physical properties, and effectively dilute expensive or hazardous functional materials. These properties make emulsions useful in a variety of products including pharmaceuticals, cosmetics, paints and inks, pesticides, and foods.
Emulsions throughout history
Emulsions in one form or another, have been used for centuries. Early societies learned to take advantage of this natural phenomenon; for example, the ancient Egyptians used eggs, berry extracts, and oils to form crude emulsified paints. In recent times, emulsions have been developed to deliver medicine in the form of ointments. Today, many products including drugs, paints and inks, cosmetics, and even certain foods, are made possible through the use of emulsions.
Emulsions are created by surfactants
An emulsion can be described as a collection of tiny droplets of one liquid (e.g., an oil) dispersed in another liquid (e.g., water) in which it, the first liquid, is insoluble. Emulsions are formed by mixing these two liquids with a third substance, known as an emulsifier, which creates a uniform, stable dispersion of the first liquid in the second.
Emulsifiers belong to the class of chemicals known as surfactants, or surface active agents, which are able to reduce the surface tension of liquids. This ability is important because surface tension, (one of the physical properties that determines how liquids behave) must be overcome for the two liquids to effectively intermingle. Surfactants are able to create this effect by virtue of the dual nature of their molecular structure. One part of the molecule is soluble in water, the other in oil; therefore, when an emulsifying surfactant is added to a mixture of oil and water it acts similar to a bridge between the two immiscible materials. This bridging effect reduces the forces between the liquid molecules and allows them to be broken into, and maintained as, separate microscopic droplets.
In an emulsion, millions of these tiny surfactant bridges surround the dispersed droplets, shielding them from the other liquid in which they are mixed. The dispersed drops are called the internal phase, the liquid that surrounds the drops is known as the external phase. Depending on the desired characteristics of the finished emulsion, either water or oil may comprise the external phase. The emulsion is further characterized by the type of charge carried by its emulsifiers: it can be anionic (containing a negative charge), cationic (containing a positive charge), or nonionic (containing no charge).
Characteristics of emulsions
The resulting emulsion has physical properties different from either of its two components. For example, while water and oils are transparent, emulsions are usually opaque and may be designed to have a lustrous, pearlized appearance. While water and oil are thin free flowing liquids, emulsions can be made as thick creams that do not flow. Furthermore, the tactile and spreading properties of emulsions are different than the materials of which they are composed.
One of the most important characteristics of emulsions is their inherent instability. Even though the dispersed drops are small, gravity exerts a measurable force on them and over time they coalesce to form larger drops that tend to either settle to the bottom or rise to the top of the mixture. This process ultimately causes the internal and external phases to separate into the two original components. Depending on how the emulsion is formulated and the physical environment to which it is exposed, this separation may take minutes, months, or millennia.
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 that 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 that 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 nonionic emulsions are used to deliver various oils and waxes that 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 divided finely into 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 influence taste because emulsified oils coat the tongue, imparting mouthfeel (or an interaction of the food’s physical and chemical characteristics with the tongue and mouth). Emulsions are useful tools in industries that 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
KEY TERMS
Anionic— A type of surfactant characterized by a net negative charge on its water soluble portion.
Cationic— A type of surfactant characterized by a net positive charge on its water soluble portion.
Dispersion— A mixture composed of tiny particles suspended in a medium such as water.
Immiscible— Compounds that will not dissolve or form solutions with one another.
Microemulsions— A dispersion mixture that consists of particles so small that it is transparent.
Nonionic— A type of surfactant that has no net charge on its water soluble portion.
Surface tension— A force that causes a liquid to resist an increase in its surface area.
Surfactant— Chemical that has both water soluble and oil soluble portions and is capable of forming nearly homogenous mixtures of typically incompatible materials. Also known as an emulsifier.
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. They 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.
Resources
BOOKS
Bibette, J. Emulsion Science: Basic Principles (An Overview). Berlin, Germany, and New York: Springer, 2002.
Pave, Marc, et al. Handbook of Cosmetic Science and Technology. New York: Taylor & Francis, 2006.
Rosen, Milton J. Surfactants and Interfacial Phenomena. Hoboken, NJ: Wiley-Interscience, 2004.
Schramm, Laurier Lincoln. Emulsions, Foams, and Suspensions: Fundamentals and Applications. Weinheim, UK: Wiley-VCH, 2005.
Sjoblom, Johan, ed. Emulsions and Emulsion Stability. Boca Raton, FL: Taylor & Francis, 2006.
Randy Schueller
Perry Romanowski
Emulsion
Emulsion
An emulsion is a two phase system of immiscible liquids in which one liquid is dispersed in the other in the form of microscopic droplets. This dispersion is achieved through the use of emulsifying agents, known as surfactants, which act as chemical bridges between the two liquids. Emulsions provide a variety of benefits such as the ability to deliver water insoluble active materials from water based products, to improve control over a product's physical properties, and effectively dilute expensive or hazardous functional materials. These properties make emulsions useful in a variety of products including pharmaceuticals, cosmetics, paints and inks, pesticides , and foods.
Emulsions throughout history
Emulsions in one form or another, have been used for centuries. Early societies learned to take advantage of this natural phenomenon; for example, the ancient Egyptians used eggs, to emulsify berry extracts, with oils to form crude emulsified paints. In more recent times, emulsions have been developed to deliver medicine in the form of ointments. Today, many products including drugs, paints and inks, cosmetics, and even certain foods, are made possible through the use of emulsions.
Emulsions are created by surfactants
An emulsion can be described as a collection of tiny droplets of one liquid (e.g., an oil) dispersed in another liquid (e.g., water) in which it, the first liquid, is insoluble. Emulsions are formed by mixing these two liquids with a third substance, known as an emulsifier, which creates a uniform, stable dispersion of the first liquid in the second.
Emulsifiers belong to the class of chemicals known as surfactants, or surface active agents, which are able to reduce the surface tension of liquids. This ability is important because surface tension, (one of the physical properties which determines how liquids behave) must be overcome for the two liquids to effectively intermingle. Surfactants are able to create this effect by virtue of the dual nature of their molecular structure. One part of the molecule is soluble in water, the other in oil; therefore, when an emulsifying surfactant is added to a mixture of oil and water it acts as a "bridge" between the two immiscible materials. This bridging effect reduces the forces between the liquid molecules and allows them to be broken into, and maintained as, separate microscopic droplets.
In an emulsion millions of these tiny surfactant bridges surround the dispersed droplets, shielding them from the other liquid in which they are mixed. The dispersed drops are called the internal phase, the liquid that surrounds the drops is known as the external phase. Depending on the desired characteristics of the finished emulsion, either water or oil may comprise the external phase. The emulsion is further characterized by the type of charge carried by its emulsifiers: it can be anionic (containing a negative charge), cationic (containing a positive charge), or nonionic (containing no charge).
Characteristics of emulsions
The resulting emulsion has physical properties different from either of its two components. For example, while water and oils are transparent, emulsions are usually opaque and may be designed to have a lustrous, pearlized appearance. While water and oil are thin free flowing liquids, emulsions can be made as thick creams which do not flow. Furthermore, the tactile and spreading properties of emulsions are different than the materials of which they are composed.
One of the most important characteristics of emulsions is their inherent instability. Even though the dispersed drops are small, gravity exerts a measurable force on them and over time they coalesce to form larger drops which tend to either settle to the bottom or rise to the top of the mixture. This process ultimately causes the internal and external phases to separate into the two original components. Depending on how the emulsion is formulated and the physical environment to which it is exposed, this separation may take minutes, months, or millennia.
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.
Resources
books
Garrett, H.E. Surface Active Chemicals. New York: Pergamon Press, 1972.
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.
Randy Schueller
Perry Romanowski
KEY TERMS
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .- Anionic
—A type of surfactant characterized by a net negative charge on its water soluble portion.
- Cationic
—A type of surfactant characterized by a net positive charge on its water soluble portion.
- Dispersion
—A mixture composed of tiny particles suspended in a medium such as water.
- Immiscible
—Compounds which will not dissolve or form solutions with one another.
- Microemulsions
—A dispersion mixture which consists of particles so small that it is transparent.
- Nonionic
—A type of surfactant which has no net charge on its water soluble portion.
- Surface tension
—A force which causes a liquid to resist an increase in its surface area.
- Surfactant
—Chemical which has both water soluble and oil soluble portions and is capable of forming nearly homogenous mixtures of typically incompatible materials. Also known as an emulsifier.
emulsion
emulsion
emulsion
e·mul·sion / iˈməlshən/ • n. a fine dispersion of minute droplets of one liquid in another in which it is not soluble or miscible.