Scattering Neutrons along the Polyelectrolyte Complex/Coacervate Continuum

The coil size of narrow molecular weight distribution deuterated poly(styrenesulfonate), PSS, within a polyelectrolyte complex doped with KBr was tracked across the continuum from solid to coacervate to solution using small-angle neutron scattering. While PSS alone in solution exhibited the familiar and pronounced “polyelectrolyte effect” of coil shrinkage with increasing [KBr], the radius of gyration R g of the PSS in the complex remained surprisingly constant up to 1.4 M KBr, which is close to the transition between complex and coacervate behavior. Thereafter, R g decreased with increasing KBr, remaining slightly larger than R g for PSS in KBr alone. Upturns in the scattering at low angle, seen for complexes in lower [KBr], are consistent with porosity, observed macroscopically as whitening of the bulk complex—a universal property of polyelectrolyte complexes. Reasons for this porosity, imaged by scanning electron microscopy, are discussed. At high q ranges, a correlation peak between deuterated coils of PSS was observed.