Characterization of size, anisotropy, and density heterogeneity of nanoparticles by sedimentation
velocity
Challenge
Materials science faces a significant
obstacle in accurately characterizing the size-dependent properties of colloidal inorganic
nanocrystals. These nanocrystals display intrinsic polydispersity during synthesis,
resulting in heterogeneity in density (ρ), molar mass (M), and particle diameter (d). The
addition of surfactants during synthesis to regulate the shape, size, and optical attributes
of these nanocrystals complicates the post-synthesis determination of the amount of
passivating ligand bound to the nanocrystal surface. Consequently, accurately gauging the
nanocrystal diameter becomes challenging due to the ligand shell's presence
Solution
The study introduced the Custom Grid
method, incorporated in UltraScan-III, as a technique to characterize nanoparticles and
macromolecules through sedimentation velocity analytical ultracentrifugation. Using CdSe and
PbS semiconductor nanocrystals, along with the ultrastable silver nanoparticle
(M4Ag44(p-MBA)30) as model systems, the researchers demonstrated that the Custom Grid method
can offer high-resolution compositional information for mixtures of solutes heterogeneous in
two of the three parameters. When one property is kept constant, this method can discern
arbitrary two-dimensional distributions of hydrodynamic attributes. As instances, the method
can derive partial specific volume and molar mass where anisotropy remains constant, or it
can pinpoint anisotropy and partial specific volume if the molar mass is predefined.
Conclusion
The Custom Grid method presents an
innovative and effective solution for the intricate challenge of characterizing
heterogeneous nanoparticles, especially in circumstances where traditional methods falter
due to the presence of added surfactants and the complexity of the inherent polydispersity
of nanocrystals. This approach can unveil crucial high-resolution compositional data for
diverse solutes, thereby bolstering the understanding and potential applications of
colloidal inorganic nanocrystals in materials science.
