What is a Microemulsion

1 What is a Microemulsion - As shown in Table 2, microemulsions, as well as emulsions, are colloidal systems. An emulsion is a thermodynamically unstable suspension of liquid droplets in a second immiscible liquid. 

The term microemulsion was initially introduced in 1959 by Schulman who suggested the following definition A microemulsion is formed on addition of an aliphatic alcohol (co-surfactant) to an ordinary emulsion. Generally, micro-emulsions are defined as thermodynamically stable homogeneous mixtures of oil and water stabilised by surfactants and, in some cases, by co-surfactants. Thus, a water in oil microemulsion, i.e. a reversed micellar solution, is a transparent, isotropic and thermodynamically stable fluid in which nanometer-sized water droplets are dispersed in a continuous oil phase. 

Three factors distinguish a microemulsion from an emulsion (i) the transparency, as the microemulsion is an optically isotropic solution, (ii) the thermodynamic stability of a microemulsion and the (iii) heterogeneity at the molecular level with droplets of the size 60-800 A (micelles). 

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What is a microemulsion This question was very much in focus when I first came in contact with the field by the end of the 1960s and early 1970s. The very fact that a question like this arises leads to considerable confusion and unnecessary work. Thus, had the true nature of microemulsions been understood, a resort to the basic literature on surfactant self-assembly would have given logical explanations to many observations. 

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