Emulsions are the mixtures of two or more type of liquids where, one is such as droplets, of tiny or even ultramicroscopic size, which are distributed throughout each other. These are usually formed from the component of liquids either in natural form or, more often, using mechanisms such as the agitation, which is provided that these fluids mixed have no kind of mutual solubility.
Some common emulsions are milk (where the dispersion of fat molecules or droplets in the aqueous solution) and also butter (which is the dispersion of droplets of particles of an aqueous solution in the fat).
Types of Emulsion:
Emulsions can be classified on the basis of the properties of the dispersed phase and the dispersion medium.
- Oil in water (O/W): In this type of emulsion, the oil will be the dispersed phase and water will be the dispersion medium. The best example for o/w emulsion is milk. In milk, the fat globules (which act as the dispersed phase) are suspended in water (which acts as the dispersion medium).
- Water in oil (w/o): In this type, water will be the dispersed phase and oil will be the dispersion medium. Margarine (a spread used for flavouring, baking and working) is an example of water in oil emulsion.
Microemulsions- In spite of their similarity, the terms microemulsion and emulsion characterize two very different systems both by their physical and thermodynamic properties and by their structure. In both cases, the systems consist of an aqueous phase, a lipophilic phase and a surfactant agent. A co-surfactant is also required for microemulsions. Microemulsions actually exist when the percentage of oil or water in the internal phase is low (<10%). These dispersions of oil or water nanodroplets in an external phase are stabilized by an interfacial film of surfactant and co-surfactant. The addition of co-surfactant results in a homogeneously dispersed system, which can diffuse the light, appear clear and homogeneous to the naked eye and, as opposed to emulsions, is thermodynamically stable. The co-surfactants have three functions: (1) they provide very low interfacial tensions required for the formation of microemulsions and their thermodynamic stability, (2) they can modify the curvature of the interface based on the relative importance of their apolar groups and (3) they act on the fluidity of the interfacial film.
The main characteristic of microemulsions is their transparent appearance due to the high level of dispersion of the internal phase, the size of which ranges from 100 to 1000 Å.
The microemulsions are Newtonian liquid and are not very viscous. These dispersed systems are isotropic and in terms of the manufacture, their formation is spontaneous, do not require much energy and are thermodynamically stable.
O/w micellar solution- Blending of a small amount of oil with water results in a two-phase system because ‘water and oil do not mix’. If the same small amount of oil is added to an aqueous solution of a suitable surfactant in the micellar state, the oil may preferentially dissolve in the interior of the micelle because of its hydrophobic character. This type of micellar microemulsion is called an o/w micellar solution.
W/o micellar solution- In these systems, sometimes called reverse micellar solutions, water molecules are found in the polar central portion of a surfactant micelle, the nonpolar portion of which is in contact with the continuous lipid phase.
A microemulsion in which a water-insoluble oil or drug is ‘dissolved’ in an aqueous surfactant system plays an important role in drug administration.
|1.||Dilution test||Emulsion can be diluted only with external phase.|
|2.||Dye test||Water-soluble solid dye tints only o/w emulsions, whereas oil soluble dye tints w/o emulsions.|
|3.||Fluorescence test||Since oils Ńuoresce under UV light, o/w emulsions exhibit dot pattern,whereas w/o emulsions Ńuoresce throughout.|
|4.||CoCl2/Filter paper test||Filter paper impregnated with CoCl2 and dried (blue) changes to pink when o/w emulsion is added.|
|5.||Conductivity test||Electric current is conducted by o/w emulsions, owing to the presence of ionic species in water.|
Table 1 – Methods for the determination of type of emulsion
Multiple choice question (MCQs)
1.Dye test which is used to identify type of emulsion is that which dye is used?
2.In conductivity test, if bulb glows on passing electric current so what would be the type of emulsion?
3.In micro emulsion, the size of globule are
4.Multiple emulsion can be designed as
d)both b and c
5.Which emulsion is mainly used for taste masking purpose?
6.Dilute emulsion follows
a)Non Newtonian flow
7.If viscosity of continous phase increase so creaming
d)None of the above
8.In case of coalescence
a)Dispersed droplet does not fuse
b)Globule size decrease
c)No. of globules increase
d)Dispersed droplets tend to fuse
9.If the density of two phase is more so
a)Stability of emulsion is less
b)Stability of emulsion is more
c)Does not affect the stability
d)None of the above
10.In case of o/w emulsion, creaming takes place at
c)At interface between two phase
d)None of the above
11.Ideal phase volume ratio per stable emulsion
12.Thermodynamically emulsion is
d)Difficult to predict
14.Upward creaming is observed in
15.HLB value of w/o emulsifying agent is
- a)Scarlet red
- b)o/w emulsion
- c)0.01 µm
- d)both b and c
- a)Multiple emulsion
- b)Newtonian flow
- d) Dispersed droplets tend to fuse
- a)Stability of emulsion is less
- b)Up side
1. GAURAV KUMAR JAIN – THEORY & PRACTICE OF PHYSICAL PHARMACY, 1st edition 2012 Elsevier, page no. 237-240.
2. Martins Physical Pharmacy, 6th edition 2011, page no. 763.