(38e) Structure and Composition of Mixed Micelles Formed By Ionic Surfactants and Nonionic Block Copolymers in Water

The interactions between surfactants and polymers in solution give rise to association structures and corresponding properties which are a strong function of the overall composition and solvent quality. The structure and composition of assemblies (mixed micelles) formed in aqueous solution between the ionic surfactant sodium dodecyl sulfate (SDS) and poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymers (Pluronics) are determined from an analysis of small-angle neutron scattering (SANS) intensity data obtained at two different contrasts. The present study concludes that the SDS+Pluronic mixed micelles include polymer and some water in the micelle core that is formed primarily by alkyl chains. This is different than what was previously reported, but is consistent with a variety of experimental observations. The effects on the mixed micelle structure and composition of the surfactant concentration and the polymer hydrophobicity are discussed in the context of interactions between the different components. Fundamental insights are thus obtained which benefit the diverse applications of complex fluids comprising surfactants and polymers.