ABSTRACT
In surfactant science, oil and water, the two nonmiscible phases, can be mixed forming a more or less stable system via the addition of amphiphilic molecules. Depending on the ability of these molecules to decrease the interfacial tension between both phases, complex uids with various isotropic or anisotropic supramolecular organizations can be formed with different length scales from nanometers up to microns as a function of their respective concentration. These molecules are called surfactants and the mixture can be investigated in terms of the solubilization of one phase in the other one. The solubilization mechanism is based on the ability of surfactants to self-assemble “laterally” in the form of a lm that originates from their amphiphilic character, that is, having a polar and an apolar part. Indeed, at relatively low concentrations, “hydrophilic” surfactants spontaneously form micelles in water by regrouping their apolar parts and by pointing out their polar parts toward water (Tanford, 1973). An opposite situation corresponds to hydrophobic surfactants assembling as reverse micelles (Eicke, 1975); aqueous phase solubilization in reverse micelles (in oil) is formed by hydrophobic surfactants pointing out their hydrophobic chains toward the oil and by regrouping their polar parts around water molecules (and solvated solute). Increasing their concentration and varying the relative proportion of water and oil, these micelles can swell and grow, interact or fuse forming gels, liquid crystals bicontinuous three-dimensional (3D) structures, or large vesicles. The development of interfaces, if it does not cost too much energy, permits a substantial increase in the system entropy that stabilizes the overall complex uid. A system like microemulsion in which the interface between oil and water is highly developed and remains uid and dynamic is a potentially interesting and important subject for investigating species exchange or partitioning, solubilization, chemical reactions across or on the interfaces.
