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 E 18B 10–SDS system (E = poly(ethylene oxide) and B = poly(butylene oxide)) development of large surfactant–polymer aggregates was observed. In the case of B 20E 610–SDS, B 12E 227B 12–SDS, E 40B 10E 40–SDS, E 19P 43E 19–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 E 40B 10E 40–SDS and E 19P 43E 19–SDS, but positive deviations for E 18B 10–SDS. Ultrasonic studies performed for the E 19P 43E 19–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.