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 sulfa te solutions. At a high water/oil ratio, the polymer is dissolved in the aq ueous solvent, and at a low water/oil ratio it is incorporated into water-s wollen bilayers or reversed droplets. With the solvent-doped mixtures, we f ound at intermediate polymer and bilayer concentrations a closed-loop lamel lar-lamellar phase separation. In reverse systems (water/oil < 1), added po lymer never enters the sponge phase L-3, even at extremely low concentratio ns. In contrast, it is present over a large concentration range in the lame llar L-alpha and the microemulsion L-2 phases. More interestingly, PEG indu ces the formation of a sponge phase, denoted L-5, lying between L-2 and L-a lpha and thereby generates a new sequence of phases. When the alcohol conte nt is increased, the sequence lamellar-sponge-micelle (L-alpha-L-5-L-2) is obtained instead of sponge-lamellar-micelle (L-3-L-alpha-L-2) as observed i n 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 bilaye r whatever the polymer size and concentration. Perturbations of inverse dro plets by solubilization of PEG were characterized by using small-angle neut ron scattering and light scattering. Upon addition of PEG, the average radi us of the droplet remains constant and the size polydispersity increases. B esides, PEG introduces an attraction between droplets which leads to a seco nd-order phase separation between two microemulsions.