Solution microstructures of the micellar phase of Pluronic L64/SDS/water system

Here we report on a study dealing with a self-assembling ethylene oxide–propylene oxide–ethylene oxidetriblock copolymer (Pluronic L64) and an anionic surfactant, sodium dodecyl sulfate (SDS), that in water at25 C form an interesting micellar region (L-phase). We have investigated the sequence of micellestructures in this L-phase across a wide interval of copolymer concentrations using phase diagram determination,steady shear, and NMR self-diffusion (pulsed gradient spin–echo, PGSE) experiments. In solutionswhich have been prepared at moderately low copolymer concentrations (ca. 20 wt.% L64) wereport on a transition from discrete micelles to bicontinuous aggregates on the addition of SDS. This changewas mainly inferred from self-diffusion coefficient patterns (i.e., the variation of copolymers and surfactantdiffusivity vs. SDS content). At midrange and at higher polymer concentrations (i.e., in the interval from 50to 80 wt.% L64) the L-phase occurred with a bicontinuous structure which was not modified by theprogressive addition of SDS. Such a bicontinuous structure was identified by the comparison of self-diffusioncoefficients of both cosolutes and the bulk viscosity (i.e., the behavior of zero-shear viscosity vs.SDS).