Characterization of Size, Anisotropy, and Density Heterogeneity of Nanoparticles by Sedimentation Velocity

Abstract

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 Grid method can be generalized to provide high resolution composition information for mixtures of solutes that are heterogeneous in two out of three parameters. For such cases, our method can simultaneously resolve arbitrary two-dimensional distributions of hydrodynamic parameters when a third property can be held constant. For example, this method extracts partial specific volume and molar mass from sedimentation velocity data for cases where the anisotropy can be held constant, or provides anisotropy and partial specific volume if the molar mass is known.

Investigation of the size–property relationship in CuInS2quantum dots

“…A possibility to determine the particle size and density in just one AUC experiment is the multidimensional approach of simultaneously fitting the sedimentation and diffusion coefficients. 51,52 For this, the frictional ratio which is the hydrodynamic diameter divided by the volume equivalent diameter has to be equal 1. For the CuInS 2 QDs investigated in this study this is a fair assumption since they are spherical in good approximation as shown by the TEM data of Fig.…”

Centrifugal classification of ultrafine particles: Influence of suspension properties and operating parameters on classification sharpness

“…Applications in particle technology have gradually evolved within the last years. A very promising example is the investigation of heterogeneity in the shape, structure, and density of nanoparticles [11][12][13]. Outside the nanometer range, this method is certainly less important because the influence of diffusion is negligible and general approaches provide sufficient accuracy for technical applications.…”

Simultaneous Identification of Spectral Properties and Sizes of Multiple Particles in Solution with Subnanometer Resolution

“…Recently, the resolution of AUC experiments has been significantly increased by applying more powerful techniques for data evaluation. [8–10] By means of this, size and shape distributions of various nanoparticles have been recently reported with high resolution. [11–12] However, due to single-wavelength detection, correlations between size and optical properties could not be resolved.…”