Salt-free aqueous solutions of polyelectrolytes: Small angle X-ray and neutron scattering characterization

We give an introduction to the application of small angle X-ray and neutron scattering techniques to the study of the structure of polyelectrolyte solutions. The goal is not to be exhaustive and to describe the latest progress in the field of polyelectrolytes but rather to present the potential of the technique. We aim to give an overview on the main features of the scattering curves, and discuss the structural information that can be drawn. We will first give the basics of small angle scattering and highlight the role played by neutron scattering and isotopic labeling. Thus, we will discuss the significance of the monomer and counterion partial scattering functions according to the scattering length densities of both components, and will emphasize the unique possibility to separate out the intra- and intermolecular correlations. Then, some examples will show how the dispersion state and the average conformation of macroions can be addressed. We will however focus on salt-free aqueous solutions of linear flexible hydrophilic polyelectrolytes in the semidilute regime.