Characterization of Size Anisotropy and DensityHeterogeneity of Nanoparticles by Sedimentation Velocity

摘要

A critical problem in materials science is the accurate characterization of the size dependent properties of colloidal inorganic nanocrystals. Due to the intrinsic polydispersity present during synthesis, dispersions of such materials exhibit simultaneous heterogeneity in density ρ, molar mass M, and particle diameter d. The density increments ∂ρ/∂d and ∂ρ/∂M of these nanoparticles, if known, can then provide important information about crystal growth and particle size distributions. For most classes of nanocrystals, a mixture of surfactants is added during synthesis to control their shape, size, and optical properties. However, it remains a challenge to accurately determine the amount of passivating ligand bound to the particle surface post synthesis. The presence of the ligand shell hampers an accurate determination of the nanocrystal diameter. Using CdSe and PbS semiconductor nanocrystals, and the ultrastable silver nanoparticle (M4Ag44(p-MBA)30), as model systems, we describe a Custom Grid method implemented in UltraScan-III for the characterization of nanoparticles and macromolecules using sedimentation velocity analytical ultracentrifugation. We show that multiple parametrizations are possible, and that the Custom Gridmethod can be generalized to provide high resolution composition informationfor mixtures of solutes that are heterogeneous in two out of threeparameters. For such cases, our method can simultaneously resolvearbitrary two-dimensional distributions of hydrodynamic parameterswhen a third property can be held constant. For example, this methodextracts partial specific volume and molar mass from sedimentationvelocity data for cases where the anisotropy can be held constant,or provides anisotropy and partial specific volume if the molar massis known.