Interactions of an anionic surfactant with poly(oxyalkylene) copolymers in aqueous solution

Abstract

The interactions of sodium dodecyl sulfate (SDS) with poly(ethylene oxide)/poly(alkylene oxide) (E/A) block copolymers are explored in this study. With respect to the specific compositional characteristics of the copolymer, introduction of SDS can induce fundamentally different effects to the self-assembly behavior of E/A copolymer solutions. In the case of the E18B10–SDS system (E = poly(ethylene oxide) and B = poly(butylene oxide)) development of large surfactant–polymer aggregates was observed. In the case of B20E610–SDS, B12E227B12–SDS, E40B10E40–SDS, E19P43E19–SDS (P = poly(propylene oxide)), the formation of smaller particles compared to pure polymeric micelles points to micellar suppression induced by the ionic surfactant. This effect can be ascribed to a physical binding between the hydrophobic block of unassociated macromolecules and the non-polar tail of the surfactant. Analysis of critical micelle concentrations (cmc∗) of polymer–surfactant aqueous solutions within the framework of regular solution theory for binary surfactants revealed negative deviations from ideal behavior for E40B10E40–SDS and E19P43E19–SDS, but positive deviations for E18B10–SDS. Ultrasonic studies performed for the E19P43E19–SDS system enabled the identification of three distinct regions, corresponding to three main steps of the complexation; SDS absorption to the hydrophobic backbone of polymer, development of polymer–surfactant complexes and gradual breakdown of the mixed aggregates.