Abstract
The aggregation behaviour of six amphiphilic poly(ethylene-propylene)-block-polyethylene oxide (PEP-PEO) copolymers in water was investigated with the aim to study systematically the influence of a growing soluble block on the structural properties of the micelle. The polymers were prepared such that they differ in the PEO content over a large range of molecular weights, while the PEP size was kept constant. The micelles were characterized by small-angle neutron scattering (SANS) involving contrast variation experiments. Data analysis was performed by a spherical core/shell model with either constant or radial decreasing density profile in the corona and constant density in the core for both cases. The main new result is that we have observed a coronal shape crossover from a micelle with homogeneous density distribution for polymers of low PEO content to a starlike micelle with a hyperbolic density profile for polymers of high PEO content. With respect to the aggregation number this corresponds to a crossover from the mean-field to the scaling behavior of a starlike micelle.