The
migration of SiO2 nanoparticles (NPs) was investigated
during agarose gel electrophoresis with various gel mesh sizes. As
a model system, spherical SiO2 NPs of different sizes were
synthesized by Stöber synthesis, and the surface was modified
by covalently binding different types of ligands to tailor the ζ-potential
as required. In the following step, agarose gels were cast with Tris/borate/EDTA
(TBE) buffer solution, thereby controlling the mesh sizes by varying
agarose concentrations, with higher concentrations leading to smaller
mesh sizes. Additionally, the applied voltage could be varied for
different electrophoretic experiments. Generally, large mesh sizes
and high applied voltages lead to faster particle migration. The migration
of SiO2 NPs occurs under two regimes: restricted migration,
where small mesh size interferes with large particles so that the
gel is acting similar to a sieve; and unrestricted migration, where
the mesh size does not influence the particles’ migration behavior
and they move according to their ζ-potential. Following these
regimes, two different mechanisms of NP separation were possible inside
agarose gels. Both mechanisms were used to separate binary mixtures
into the former individual fractions, as proven by scanning electron
microscopy (SEM) or the ninhydrin test.
Atomic-scale characteristics of individual nanocrystals (NCs), such as the crystallographic orientation of their facets and the kind and density of crystal structure defects, play a tremendous role for the functionality and performance of the whole NC population. However, these features are usually quantified only for a small number of individual particles, and thus with limited statistical relevance. In the present work, we developed the multiscale approach available in transmission electron microscopy (TEM) further, and applied it to describe features of different types of Au NCs in a statistical and scale-bridging manner. This approach combines high-resolution TEM, which is capable of describing the characteristics of NCs on atomic scale, with a semi-automatic analysis of low-magnification high-angle annular dark-field scanning TEM images, which reveals the nanoscopic morphological attributes of NCs with good statistics. The results of these complementary techniques are combined and correlated. The potential of this multiscale approach is illustrated on two examples. In the first one, the habitus of Au NCs was classified and assigned to multiply twinned nanoparticles and nanoplates. These classes were quantified and related to different stacking fault densities. The second example demonstrates the statistical determination of crystallographic orientations and configurations of facets in Au nanorods.
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