(148c) Multidimensional Nanoparticle Characterization

An important trend in particle science and technology is the requirement to understand and design systems of ever increasing complexity. Available techniques for particle characterization are predominantly focused on size characterization, even simultaneous size and shape characterization is a major challenge, in particular for nanoparticles. Property functions as a comprehensive description of such particle systems must address both, single particles and the structure of their assemblies. The property function defines the target in product design and is understood along the five dimensions of particle size, particle shape, particle surface, particle structure (i.e. amorphous, crystalline, internal pore size distributions and defects), particle composition and their respective distributions. While the characterization of 1D particle size distributions is well established, the independent description and measurement of two or more distributed properties of a particle ensemble is a highly challenging task. Recent progress in the description and characterization of multivariate particle property distributions will be presented and discussed [1].

The typical way of particle characterization via imaging technologies like optical image analysis, SEM or TEM allow access to the 2D projections of particles. AFM imaging together with statistical RAMAN mapping can provide information on particle dimensions together with information on the complex chemical composition. Most of these techniques, in particular those for submicron particles, are very time-consuming, require complex sample handling and share the common problem of poor statistics. The obtained information is based on a limited number of counts and does not necessarily contain sufficient particles to approximate the underlying nD distributions properly.

Progress in analytical ultracentrifugation (AUC) combines outstanding resolution with high reproducibility down to particles of 1 nm in size. Novel sensors based on absorption and emission optics [2] provide access to the optical properties of size-selected nanoparticles. This allows accurate the size measurement of multimodal samples due to the excellent separation power in strong centrifugal fields. In principle, all particle systems with size, shape or compositional, respectively density, dependency of sedimenation and optical properties can be analyzed avoiding tedious TEM- or AFM-based counting. AUC was employed for the efficient characterization 2D materials such as graphene oxide or MoS₂ giving fast access during process development. Full 2D characterization of core-shell nanoparticles by the analysis of sedimentation profiles based on sedimentation and diffusion properties are demonstrated and validated by combined SAXS/SANS measurements. This enables, for instance, the characterization of size-band gap dependencies of quantum dots. Recent approaches based on size-dependent optical properties of plasmonic nanoparticles allow to measure full number-weighted 2D distributions of size and length distributions of gold nanorods or of 5-sided gold double pyramids in one single experiment [3,4]. In a similar approach, size and compositional distributions of noble metal alloy nanoparticles can be obtained [5]. Analytical ultracentrifugation is considered as gold standard in nanoparticle characterization due to the unprecedented resolution, accuracy and reproducibility.

Funding by DFG of the Collaborative Research Center 1411 “Design of Particulate Products” is greatfully acknowledged (https://www.crc1411.research.fau.eu/).

References

[1] Frank U., Uttinger M.J. Wawra S.E., Lübbert C., Peukert W., Progress in multidimensional particle characterization, KONA (invited review) 39 (2022) 3-28

[2] Lautenbach V., Onishchukov, G., Wawra S., Frank U., Hartmann L., Peukert W., Walter J., Development of an advanced multiwavelength emission detector for the analytical ultracentrifuge, Nanoscale Advances (2024), in press

[3] Wawra S., Thajudeen T., Pflug L., Kryschi C., Stingl M., Peukert W., Determination of the two-dimensional distributions of gold nanorods by multiwavelength analytical ultracentrifugation, Nature Communications 9 (2018) 4898

[4] Frank U., Drobek D., Sanchez-Iglesias A., Wawra S., Nees N., Walter J., Pflug L., Apeleo Zubiri B., Spiecker E., Liz-Marzan L., Peukert W., Determination of 2D particle size distributions in plasmonic nanoparticle colloids via analytical ultracentrifugation - Application to gold bipyramids, ACS Nano 17 (2023) 5785-5798

[5] Cardenas Lopez, P., Uttinger M.J., Traore N.E., Drobek D., Apeleo Zubiri B., Spiecker E., Peukert W., Walter J., Multidimensional characterization of noble metal alloy nanoparticles by multi-wavelength analytical ultracentrifugation, Nanoscale 9 (2022) 14, 12928-12939