Statistical Thermodynamics of Water-in-Oil Microemulsions Stabilized with an Ionic Surfactant

We present a review of theoretical studies dealing with the statistical thermodynamics of water-in-oil (w/o) microemulsions and application thereof for the synthesis of nanoparticles. The general theory of composition fluctuations in reverse micelles has been described. For w/o microemulsions based on ionic surfactants, a model has been formulated, which enables one to explain the experimentally observed spherical shape of reverse micelles, to calculate the enthalpy of water solubilization and the chemical potentials of water and surfactants, and to plot the phase diagrams of the microemulsions. Two models that explain limitation of nanoparticle growth in w/o microemulsions have been described, namely, a thermodynamic model, which is based on the search for the minimum free energy of a nanoparticle-containing microemulsion, and a kinetic model based on the consideration of the coagulation activation energy of nanoparticles as depending on their sizes and the water-to-surfactant molar ratio.