Interactions between high-molecular-weight poly(ethylene oxide) and sodium dodecyl sulfate

In this work, we study interactions between poly(ethylene oxide) (PEO) and sodium dodecyl sulfate (SDS) in aqueous solutions, using surface tension, electrical conductivity and shear rheometry. The main distinguishing feature of this investigation with respect to previous works is the use of high-molecular-weight PEOs (up to 8 × 10⁶ g/mol). The aggregation pattern of the surfactant in the form of micellar aggregates attached to the polymer chain causes specific changes in surface tension, electrical conductivity and zero-shear-rate viscosity that qualitatively resemble those found previously for lower-molecular-weight PEOs when no additional electrolytes are present in the solution. In the presence of 0.1 M NaCl and for PEOs with molecular weights of 600,000 g/mol and more, the electrical conductivity and surface tension of the solutions remain constant when surfactant is added beyond the critical aggregation concentration, until saturation of the polymer with micellar aggregates is achieved. This behavior indicates complete complexation of the dodecyl sulfate ions into micellar aggregates attached to the polymer, as well as a strong binding of the counterions to the PEO/SDS complex.