Aggregation behavior of poly(butadiene-b-ethylene oxide) block copolymers in dilute aqueous solutions: Effect of concentration, temperature, ionic strength, and type of surfactant

The aggregation behavior of a series of poly(butadiene-b-ethylene oxide) block copolymers was investigated in dilute aqueous solutions by static and dynamic light scattering and by viscometry. The aggregation number, size, and polydispersity of the micelles were found to depend on molecular weight and composition of the parent block copolymers. Apart from spherical micelles, micellar clusters and cylindrical micelles were found in some cases. Measurements at different temperatures indicate shrinkage of the spherical micelles by increasing temperature. The presence of NaCl in solution has minimal effects in the structural characteristics of the aggregates. In contrast, the presence of low molecular weight surfactants, namely, sodium dodecyl sulfate and dodecyltrimethylammonium bromide, was found to have a profound effect on the type, size, shape, and polydispersity of the aggregates.