SAXS Investigations of Structure and Phase Behavior of Polyelectrolyte–Nanoparticle Assemblies

Aqueuous mixtures of oppositely charged polyelectrolytes (PE) and nanoparticles (NP) self-assemble into dense complexes. This self-assembly forms the basis of diverse phenomena ranging from flocculant action in water treatment, where the PE-NP flocs phase separate and sediment, to DNA compaction around histone proteins into chromatin. Factors such as the PE length, architecture and concentrations; NP charge, morphology and concentrations; and solution conditions (pH and ionic strength) play key roles in directing these PE-NP assemblies. In this presentation, we will delineate fundamental investigations into the phase behavior and structure of polycation-silica NP assemblies using small angle X-ray scattering, turbidimetry and thermogravimetric analysis with systematic variation of PE sizes and flexibility, NP sizes, and a wide range of concentrations of both components. Trends in interparticle spacings and correlations as well as fractal dimensions of assemblies with varying PE and NP concentrations will be discussed, presenting a comprehensive narrative of the hierarchical structure of PE-NP self-assemblies. Near-contact compaction of NPs in the PE-NP assemblies above a critical ratio of PE and NP concentrations will be highlighted.