N. Kozlovich et al., FLUCTUATION MECHANISM OF THE DIELECTRIC POLARIZATION OF WATER-IN-OIL MICROEMULSIONS WITH IONIC SURFACTANT, Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics, 58(2), 1998, pp. 2179-2187
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.