All substances around us can be classified as elements, compounds and mixture. Elements are considered as pure substance which exhibits all the chemical and physical properties of that substance. The combination of more than one element results the formation of compounds. Mixture can be defined as the combination of two or more substances which retain their identity. On the basis of phases, mixture can be classified as homogeneous and heterogeneous mixture. In a homogeneous mixture, the components are distributed uniformly throughout the mixture. For example mixture table salt or sugar in water forms a uniform solution. The particles cannot be seen by naked eyes and cannot separate by physical methods. Heterogeneous mixtures have two or more separate phases of components.
For example mixture of sand in water makes a heterogeneous mixture. When we mix them sand gets mix with water. After some time sand particles settle down at the bottom of mixture. The particles are visible in this mixture. Usually homogenous mixtures are called as solutions. A solution is composed of solute and solvent. Here solute is present in lesser amount compare to solvent. Like in a solution of table salt, water is solvent and table salt is solute. On the basis of particles size, mixtures can be classified as true solutions, colloidal solutions and suspension. The particle size in true solutions is less than 1 nm. Because of small size, particles in true solutions are not visible by naked eyes. They are homogenous solution. The particles can diffuse rapidly through filter paper as well as parchment paper so cannot filter. Due to small particle size, these solutions do not show Tyndall effect. They are transparent solutions.
Unlike true solutions, suspensions are heterogeneous solutions as the particle size is bigger than 1000 nm. Due to large size, particles do not pass through filter paper and parchment paper and can be seen by naked eyes. They are opaque and may or may not show Tyndall effect.
Colloidal solutions have intermediate properties of true solutions and suspension. The particle size in colloidal solutions lies from 1 to 1000 nm. They are heterogeneous solutions in which Colloidal particles pass through filter paper but not through parchment paper. The particles of colloidal solutions cannot be seen to naked eye. They can be studied through ultra microscope. They are translucent solutions and can show Tyndall effect. In colloidal solutions, a dispersed phase remains disperse in dispersion medium. On the basis of phases of dispersed medium and phase, colloidal solutions can be different types such as foams, emulsions and sols.
In foam, gas is disperse phase which is liquid disperse medium. The distribution of gas in liquid makes it foamy like shaving cream. Emulsions can be defined as the colloidal solutions in which both the disperse phase and dispersion medium are in liquid state. For example mixture of oil in water or water in oil is an example of emulsion. Some common examples of emulsion are milk or mayonnaise. Another type of colloidal solutions is named as sol. In these solutions, solid phase is dispersed in liquid medium. Blood, paint are most common examples of sol.
We can observe many examples of emulsion in everyday life. For example vinaigrette, mayonnaise, mustard, honey and milk are some common examples of emulsions. Cosmetic products like body lotions and creams are also emulsions. Different drugs and medicines like balms, creams, pastes, and ointments are also emulsion solutions.
Micro emulsions are widely used in vaccination process. Milk is also an emulsion as fat droplets are dispersed liquid medium. Many self-mixed salted sauces are examples of emulsions. Emulsifiers are used to stabilize the emulsion. Egg yolks and some mustard are good examples of emulsifiers.
One of the best applications of emulsion in pharmacy is use as drug carriers. Now a day we know a large number of emulsions which are widely used for solubilizing drugs that control their release in body. These emulsions can be delivered by oral, topical, and parenteral. Oil in water emulsions can effectively use for oral absorption and can enhance the bio-availability of less soluble drugs such as griseofulvin, phenytoin and theophylline. In the oral administration of water in oil emulsion has ovalbumin which is a model antigen. This can enhance the immunogenic response.
We can observe several emulsions in our everyday life. Many emulsions are important part of our regular diet. For example, mayonnaise, vinaigrette and homogenized milk are emulsions. Similarly butter, cream, sauce, margarine, ice cream, salad dressings, sausages are also emulsions.
Usually some emulsifier is added to the packaged food item to stabilize them. For example Lecithin, proteins, gums, egg yolks act as emulsifier for different food stuff. These emulsifiers have lecithin and cholesterol that help them to bind with sauces like mayonnaise. Vinaigrette is an emulsion of oil in vinegar whereas Mayonnaise and Hollandaise sauce are oil-in-water emulsions. Egg yolk is used as emulsifier for these emulsions. Today we have many artificial emulsifiers also such as monodiglycerides and diglycerides of fatty acids and also esters.
Let’s discuss 3 most common examples of emulsions. Milk is an emulsion in which fat droplets are dispersed in liquid medium. Presence of casein stablises this emulsion so we can say that it acts as emulsifier for milk. The fat globules in milk range from 0.1 to 15 micrometers in size. Similarly butter is an emulsion of water in fats. So we can say that butter is water in oil type of emulsion. Another common example of emulsion is cream. Cream is oil in water emulsion.