Film and Solubilisation Theories of Microemulsions

According to the second law of thermodynamics, the free energy of formation of microemulsions AG is given by the following expression, 

In the case of macroemulsions, AAyi2 TAS and AG , 0, and the system is nonspontaneous (i.e., it requires energy for formation of the emulsion drops) and thermodynamically unstable. In the case of microemulsions, AA/jj TAS  

The above analysis shows the contrast between emulsions and microemulsions. 

With emulsions, an increase of the mechanical energy and an increase in surfactant concentration usually results in the formation of smaller droplets which become kinetically more stable. With microemulsions, however, neither mechanical energy nor any increase in surfactant concentration can result in their formation. The microemulsion is based on a specific combination of surfactants and specific interaction with the oil and the water phases, and the system is produced at optimum composition. 

microemulsions have nothing in common with macroemulsions, and in many cases it is better to describe the microemulsion system as swollen micelles. The best definition of microemulsions is as follows [3] System of Water -I- Oil -I- Amphiphile that is a single Optically Isotropic and Thermodynamically Stable Liquid Solution. Amphiphiles refer to any molecule that consist of a hydrophobic and hydrophilic portions, for example surfactants and alcohols. 

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