Concluding Remarks

Small angle x-ray scattering and static light scattering have been applied since the 1940s to obtain structural information on polymer solutions, though the limit of zero concentration was required to eliminate interchain interference. Thus, these methods could not be applied to the solutions of interacting macromolecules, due to the difficulties of separating the inter- and intra-chain contributions to the structure. However, SANS has removed this limitation and due to a fortuitous combination of several factors: high bulk penetrating power, the ability to manipulate local scattering amplitudes through isotopic labeling or an appropriate choice of solvent (contrast variation), the technique has developed into an extremely powerful tool for the study of polymers. By deuterating a fraction of the polymer, it is possible to measure the single-chain structure factor and thus the Rg of the individual polymer chains in strongly correlated systems. That approach provides exceptional means for investigating the structure of various complex fluids, e.g. solutions of synthetic and biological polyelectrolytes. Recent SANS and DLS

measurements demonstrate a striking universality between structure, thermodynamic and dynamic properties of sub- and supercritical polymer solutions.

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