Lakhasly

4 - Micro emulsion Formulation The properties of the surfactant-oil-water are important in determining the formation of micro emulsions.The formation of a micro emulsion depends on factors such as: (1) oil/surfactant and surfactant/co-surfactant ratio; (2) nature and concentration of the oil, surfactant, co-surfactant and aqueous phase; (3) pH; (4) temperature; and (5) hydrophilicity / lipophilicity of polarity (Bolzinger, et al., 1998; Salager, 2000).4.1 - Formulation Considerations A micro emulsion generally consists of four different components, a lipophilic phase, a hydrophilic phase, surfactant and co-surfactant (Scriven, 1976).The quantities of different substances present, are also likely to change the properties, and are referred to as composition variables which can be expressed as weight, percentage or proportion (Salager, 2000).When four or more components are used pseudo-ternary phase diagrams are used to depict these systems in which each corner represents binary mixtures of two components such as surfactant/co-surfactant, surfactant/water, oil/drug, and water/drug mixtures.

4 - Micro emulsion Formulation
The properties of the surfactant-oil-water are important in determining the formation of micro
emulsions. Deviations from the actual formulation may cause the breaking of the micro emulsion
and formation of an unstable macro-emulsion.
4.1 - Formulation Considerations
A micro emulsion generally consists of four different components, a lipophilic phase, a hydrophilic
phase, surfactant and co-surfactant (Scriven, 1976). The nature of the components like the oil,
surfactant, co-surfactant and water, as well as temperature and pressure which affect the micro
emulsion systems are known as the formulation variables. The quantities of different substances
present, are also likely to change the properties, and are referred to as composition variables which
can be expressed as weight, percentage or proportion (Salager, 2000). In order that the micro
emulsions attain low interfacial tension and good solubilisation ability, it is necessary that the micro
emulsions be formulated accurately. The formation of a micro emulsion depends on factors such as:
(1) oil/surfactant and surfactant/co-surfactant ratio; (2) nature and concentration of the oil,
surfactant, co-surfactant and aqueous phase; (3) pH; (4) temperature; and (5) hydrophilicity /
lipophilicity of polarity (Bolzinger, et al., 1998;
Salager, 2000). All these factors must be considered during the formulation of micro emulsions.
Moreover, it is important to consider the compatibility of the oil, surfactant or co-surfactant for the
desired route of administration.
To study the phase behaviour of simple micro emulsion systems comprising of surfactant, oil and
water at fixed pressure and temperature ternary phase diagrams are used. Each corner of the
ternary phase diagram represents 100% concentrations of a particular component. When four or
more components are used pseudo-ternary phase diagrams are used to depict these systems in
which each corner represents binary mixtures of two components such as surfactant/co-surfactant,
surfactant/water, oil/drug, and water/drug mixtures. A typical ternary phase diagram is shown in
Figure 3.3 (Shaji, 2004)