Effect of Confinement of a Polymer on the Phase Behavior of Ternary and Quaternary Lyotropic Mixtures

In this paper, we examine the effect of adjunction of poly(ethylene glycol) (PEG) on the phase behavior of water−dodecane−hexanol−sodium dodecyl sulfate solutions. At a high water/oil ratio, the polymer is dissolved in the aqueous solvent, and at a low water/oil ratio it is incorporated into water-swollen bilayers or reversed droplets. With the solvent-doped mixtures, we found at intermediate polymer and bilayer concentrations a closed-loop lamellar−lamellar phase separation. In reverse systems (water/oil < 1), added polymer never enters the sponge phase L3, even at extremely low concentrations. In contrast, it is present over a large concentration range in the lamellar Lα and the microemulsion L2 phases. More interestingly, PEG induces the formation of a sponge phase, denoted L5, lying between L2 and Lα and thereby generates a new sequence of phases. When the alcohol content is increased, the sequence lamellar−sponge−micelle (Lα−L5−L2) is obtained instead of sponge−lamellar−micelle (L3−Lα−L2) as observed in the polymer-free system. X-ray studies show that the incorporation of PEG in the inverse lamellar phase has no effect on the thickness of the bilayer whatever the polymer size and concentration. Perturbations of inverse droplets by solubilization of PEG were characterized by using small-angle neutron scattering and light scattering. Upon addition of PEG, the average radius of the droplet remains constant and the size polydispersity increases. Besides, PEG introduces an attraction between droplets which leads to a second-order phase separation between two microemulsions.