N. Kozlovich et al., EFFECT OF CHARGE-DENSITY FLUCTUATIONS WITHIN A DROPLET ON DIELECTRIC POLARIZATION OF IONIC MICROEMULSIONS, Colloids and surfaces. A, Physicochemical and engineering aspects, 140(1-3), 1998, pp. 299-312
A statistical model of the dielectric polarization of ionic water-in-o
il microemulsions is proposed. The model makes it possible to describe
the effect of temperature and dispersed phase content on the static d
ielectric permittivity behavior of the microemulsions at a region far
below percolation. With the help of this model, the microemulsions for
med with the surfactant, sodium bis(2-ethylhexyl) sulfosuccinate (AOT)
, have been analyzed. The studied systems are considered to consist of
nanometer-sized spherical non-interacting water droplets of equal siz
e with negatively charged head groups SO3-, staying at the interface a
nd positive counterions Na+, distributed in the electrical diffuse dou
ble layer of the droplet interior. It can be conjectured that two diff
erent mechanisms, that provide an increase of the static dielectric pe
rmittivity as a function of temperature, may take place. These may be
attributed either to the aggregation of droplets or the temperature gr
owth of polarizability of non-interacting and therefore non-aggregatin
g droplets dispersed in oil. The results support the hypothesis that t
he experimental temperature behavior of dielectric polarization far be
low the percolation region is only due to the polarization of a single
droplet and not to an aggregation. The droplet polarizability is prop
ortional to the fluctuation mean-square dipole moment of a droplet. It
is shown that this mean-square dipole moment and the corresponding va
lue of the dielectric increment, depend upon the equilibrium distribut
ion of counterions within a diffuse double layer. The density distribu
tion of ions is determined by the degree of the dissociation of the io
nic surfactant. The dissociation of the ionic surfactant in the system
has been analyzed numerically. The relationship between the constant
of dissociation and the experimental dielectric permittivity has been
ascertained. (C) 1998 Elsevier Science B.V. All rights reserved.