Quantitative analysis of nanoparticle interactions and their distributions

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Nanoparticle interactions are essential for the understanding of all colloidal systems. However, so far, only few methods exist for their determination like isothermal titration calorimetry, yielding average values. However, nanoparticles are usually not monodisperse and exhibit a distribution of properties. This project addresses this fundamental yet unsolved problem and develops new methodology to determine size- and shape-dependent distributions of dissociation constants, stoichiometry and cooperativity of aggregating nanoparticles using combined sedimentation (s)- and diffusion coefficient (D) distributions from Analytical Ultracentrifugation. These distributions are available as contour maps and a set of binding isotherms can be obtained for different nanoparticle concentrations. Fitting to an appropriate binding model yields the dissociation constant, stoichiometry and cooperativity for each isotherm resulting in a distribution of these constants in dependence of s and D. From the s- and D-distributions, the size, shape and particle density distributions can also be obtained and correlated to the interaction constant distributions. The methodology will first be established for monodisperse spherical particles. Later, interaction constant distributions will be determined for polydisperse spherical nanoparticles and subsequently also anisotropic nanoparticles like nanorods. For anisotropic nanoparticles, crystal face dependent interactions shall be characterized for different concentration regimes. Finally, aggregating nanoparticles with different shape and material will be investigated to reveal the influence of shape versus material onto the nanoparticle interactions.