Hr. Rabie et al., COMPARISON OF THE TITRATION AND CONTACT METHODS FOR THE WATER SOLUBILIZATION CAPACITY OF AOT REVERSE MICELLES IN THE PRESENCE OF A COSURFACTANT, Journal of colloid and interface science, 189(2), 1997, pp. 208-215
The method used to form a reverse micellar phase determines the amount
of water solubilized in the organic phase. The effect of cosurfactant
and salt on the water solubilization capacity per mole of surfactant
was determined for two methods of solubilization: contact with an exce
ss aqueous phase and the titration method. The two methods are intrins
ically different. While in the titration method, there is a transition
from a Winsor IV system to either Winsor I or II system, in the conta
ct method, the experiments are always in a Winsor II system. When the
titration method was used at low salt concentrations, or even without
salt, the water solubilized increased with the concentration of cosurf
actant, at low cosurfactant concentrations. When the contact method wa
s used, the water solubilized per mole of surfactant decreased with an
increase in the cosurfactant concentration. When titration was used,
at a fixed cosurfactant-to-surfactant molar ratio, several solubilizat
ion capacities were obtained at low salt concentrations, whereas a sin
gle solubilization capacity was found when the titrant had a higher sa
lt content. With the contact method, a single solubilization capacity
was observed for all salt concentrations at which reverse micelles wer
e formed. When the same salt solution was used as the titrant in the t
itration method and the initial excess aqueous phase in the contact me
thod, a larger amount of water was solubilized by the latter method. (
C) 1997 Academic Press.