FLUCTUATION MECHANISM OF THE DIELECTRIC POLARIZATION OF WATER-IN-OIL MICROEMULSIONS WITH IONIC SURFACTANT

A statistical model is proposed to describe the dielectric polarizatio n of ionic microemulsions at a region far below percolation in which t he microemulsions consist of spherical single droplets with water in t he central core surrounded by a layer of surfactant molecules. The mod el describes the effect of temperature and dispersed phase content on the behavior of the dielectric polarization of ionic water-in-oil micr oemulsions and explains the experimentally observed increase of the st atic dielectric permittivity as a function of temperature. The microem ulsions formed with surfactant sodium bis(2-ethylhexyl) sulfosuccinate have been analyzed with the help of this model. The systems are consi dered to consist of nanometer-sized spherical noninteracting water dro plets of equal size with negatively charged head groups, staying at th e interface, and positive counterions, distributed in the electrical d iffuse double layer of the droplet interior. It is shown that the drop let polarizability is proportional to the mean-square fluctuation dipo le moment of the droplet. This mean-square dipole moment and the corre sponding value of the dielectric increment depend on the equilibrium d istribution of counterions within a diffuse double layer. The density distribution of ions is determined by the degree of the dissociation o f the ionic surfactant. The relationship between the dielectric permit tivity, the constant of dissociation of surfactant, the content of the dispersed phase, and the temperature has been ascertained.