Microemulsions: Some Basic Concepts

Abstract

Quite early in the history of studies on micelle formation, it was understood that the core of a micelle could take other substances. This involves the term “solubilization” which was defined as a method of “bringing into solution substances that are otherwise insoluble in a given medium” [1]. It may not be difficult to appreciate that the concept of solubilization is associated with and follows those of surfactant aggregation and micelle formation. Figure 3.1 gives only a general idea, and more details will be discussed through this Chapter. The phenomenon should be valid, with obvious differences, for both normal and reverse micelles. The latter is especially important for us, because when we have solubilized a certain minimum amount of water (or an aqueous solution or a sol) in the core of a reverse micelle, we have progressed from reverse micelles to the so-called “swollen micelles”; with further increase in water, we have a water pool that is several times larger than the ordinary “dry” core, and has been used by various workers as “nanoreactors” for particle synthesis. As dictated by the respective phase behavior of a surfactant/oil phase/water phase, the system may form a W/O (reverse) microemulsion in a certain specific (oil-rich) compositional domain (Section 3.2). By the same logic, with oil droplets in the cores of normal micelles and water as the continuous phase, a O/W microemulsion may form in another, water-rich, compositional domain.