Ordering of urchin-like charged copolymer micelles: Electrostatic, packingand polyelectrolyte correlations

We report the results of small-angle neutron scattering (SANS) studies on a queous solutions of spherical polyelectrolyte micelles formed by associatio n of charged-neutral diblock copolymers. The neutral moieties are found to self-assemble into small dense spheres (cores of the micelles) whose sizes are independent of the polymer concentration c. In the dilute regime, c < c *, where c* is the overlap concentration of the micelles, the conformation of the charged groups, which form the corona of the micelles, is found to b e extended. A liquid-like order is observed over a wide concentration range spanning from the dilute regime to the concentrated regime. For c > c*, po lyelectrolyte correlations appear at smaller spatial scales and coexist wit h the liquid-like order. These results suggest that for dense brushes, abov e c*, the rod-like statistics of the charged chains begin to disappear due to contraction of corona arms or by interpenetration of coronae. For less d ense brushes, the charged chains are found to be extended up to concentrati ons far above c*, before the progressive development of polyelectrolyte cor relations.