ABSTRACT
Static light scattering and dynamic light scattering are useful experimental tools for the investigation of the structure and dynamics of polyelectrolyte solutions as well as for the characterization of polymer systems in general. The structure can be probed by static light scattering (SLS) on a certain length scale (typically from 20 nm to several microns) limited mainly by the light wavelength. Therefore the accessible structural information is usu ally on the level of a whole polymer chain, interchain correlations, and the solution structure on a large length scale exceeding single chain dimensions and interchain separation distances. Light scattering does not yield direct information on the local structure inside the chain, referred to also as the primary and secondary structure. However, smaller length scales can be probed by very similar techniques in which x-rays or neutrons are used instead of visible light (small-angle x-rays and small-angle neutron scatter ing). The dynamics probed by dynamic light scattering (DLS) is limited by the technical possibilities of currently available instrumentation (from ca 0.5 μ£ to seconds). Naturally, the dynamics is related also to the structure. Therefore some structural information can be calculated from the dynamic data, too. In this case, the length scale probed is not limited by light wave length and extends below 1 nm. Charge interactions in polyelectrolyte so lutions dominantly influence the structure and dynamics on the above-men tioned length and time scales, and therefore light scattering is a source of information on the character of these interactions. Absolute values of scat tering intensities are thermodynamic quantities that enable us under certain circumstances to calculate such important parameters as polymer molecular weight or the second virial coefficient in the virial expansion of osmotic
pressure. As will be shown throughout this chapter, light scattering from polyelectrolyte solutions is a rather complex and variable subject, and the interpretation of light scattering data is often a nontrivial task. The aim of this chapter is to present the issue of the structure and dynamics of poly electrolyte solutions by light scattering in a compact form. It is based on the author’s own work, which is complemented by selected literature results. It is not intended to be a complete review, and therefore the selection of cited literature is to some extent personal. We acknowledge at this point many valuable works in the field that are not included. Our presentation is focused mainly on linear flexible polyelectrolytes, but many properties are universal and apply also to other polyelectrolyte classes unless explicitly specified in another way. Excluded is the case of polyelectrolyte solutions with multivalent counterions, which will be discussed in a different chapter, and some other special cases specified in the text.
