EFFECT OF ADSORBING POLYELECTROLYTES ON A BALANCED NONIONIC SURFACTANT-WATER-OIL SYSTEM

We have studied the effects of an adsorbing polyelectrolyte (hydrophob ically modified sodium polyacrylate) on the phase behavior of a balanc ed nonionic surfactant-water-oil system. As seen from the variation of phase volumes in a three-phase (Winsor III) equilibrium, the effect o f polymer adsorption can be described as an increase of the spontaneou s curvature of the film away from water. With increasing polymer conce ntration the middle phase microemulsion first increases its water-to-o il ratio, whereas above a certain polymer concentration the trend is r eversed. Following Kabalnov(1) et al., this reversal is interpreted as a saturation in the polymer adsorbtion. The saturation value correspo nds to approximately 0.2 mg of polymer per m(2) of the surfactant film and is similar to that in the Kabalnov experiment with a different po lymer. The phase behavior at equal volumes of water and oil was also s tudied as a function of surfactant concentration for various aqueous p olymer concentrations. While the polymer is readily soluble in the mic roemulsion phase with bicontinuous topology, its solubility in the lam ellar phase, where the surfactant (bilayer) film is planar. was found to depend on the polymer concentration and added salt. The results dem onstrate that film topology and electrostatic interactions are importa nt factors determining the polymer compatibility with these surfactant phases.