A SURFACTANT-WATER-OIL SYSTEM WITH WEAKLY CHARGED FILMS

We have studied the effects on microstructure and phase equilibria of a nonionic surfactant-water-oil system when replacing one per hundred of the surfactant molecules by ionic surfactant, sodium dodecyl sulfat e (SDS). This degree of substitution corresponds to introducing approx imately one charge per 4400 Angstrom(2). The nonionic surfactant syste m contains pentaethylene glycol dodecyl ether (C(12)E(5)), water, and decane, at a constant surfactant to oil weight ratio of 52/48. The wat er content is varied from 60 to 100 wt %. In this composition range th e initial phase sequence consisted of L(1) phase-lamellar phase-L(3) p hase as a function of increasing temperature. Adding the small amount of SDS has a large impact on the phase behavior. A reverse hexagonal p hase (H-2) and a reverse micellar microemulsion phase (L(2)) are added to the phase sequence at temperatures above the L(3) phase. The micro structures in the different phases were studied by the NMR self-diffus ion technique and by small angle X-ray scattering.