Phase equilibria of polymer-containing microemulsions

This paper reports experimental results of the effect of poly(ethylene glycol) (PEG) on the phase behavior of the system made of sodium bis(2-ethylhexyl)sulfosuccinate (Aerosol OT)water/isooctane. Although the microemulsions and the lamellar phases still exist when pure water is replaced with aqueous solutions of PEG, their stability is significantly affected. It has been found that (1) large amounts of polymer can be solubilized in the lamellar and microemulsions phases, up to 17% in weight of water can be replaced by polymer, (2) the solubility of PEG in the water-in-oil droplets depends on the relative sizes of the water core (R-W) and the polymer (R-G) and on temperature; (3) at high R-W/R-G ratios, PEG enhances the solubilization of water in oil, and (4) PEG changes the sign of the spontaneous curvature of the surfactant film and induces an inversion of microemulsion type from oil-in-water to water-in-oil. This effect is similar to that produced by addition of NaCl. Interestingly enough, there exists a PEG concentration range, where the hydrophile-lipophile property of AOT is just balanced at T = 25 degrees C. Finally electrical conductivity and Light scattering data indicate that the presence of PEG in the water core of inverse micelles leads to a decrease of the attractions between the micelles.