Intermolecular structure of spherical polyelectrolyte microgels in salt-free solution.: 1.: Quantification of the attraction between equally charged polyelectrolytes

Static light scattering experiments were performed on spherical polyelectrolyte microgels in dilute aqueous solution. These particles realize a model system that is close to a "pure Coulombic" and "conformation-change free" polyelectrolyte. A more complete picture than in other studies is provided by the systematic examination of macroions over 1 decade of radii (6 nm < R < 70 nm), with its mesoscopic range of molecular mass for the first time covering the gap between linear polyelectrolytes and classical latex spheres. Solution structuring, phase-separation behavior, and concentration dependence of interparticle distances prove the presence of electrostatic attractive forces. This is confirmed by salt concentration and cross-linking-density-dependent experiments. Scattering data are also analyzed in the framework of Coulomb potential/MSA within the primitive model showing the existence of effective repulsive and attractive forces. On the basis of the experimental data, two qualitative pictures for the attraction mechanism are discussed: the "fluctuation model" and the "colloidal orbital approach".