| Abstract: |
Due to the continous increase of complexity and associated functional properties of particulate systems, multi-parameter characterization methods are required to comprehensively describe particle-based phenomena. The technique of analytical ultracentrifugation equipped with a multi-wavelength extinction detector (MWL-AUC) enables the simultaneous measurement of extinction spectra and sedimentation properties of nanoparticles, from which two-dimensional property distributions can be derived. (Wawra et al., 2018)
In our contribution, we present a new analytical method, which combines sedimentation and extinction properties of nanoparticles during gravitational sweep experiments to obtain two-dimensional size-composition distributions of gold-silver alloy nanoparticles. The extinction cumulative distribution of the retrieved AUC data is divided into a finite number of intervals with corresponding mean sedimentation coefficients. This enables the retrieval of interval representative optical spectra. Furthermore, the hydrodynamic particle diameters are resolved. Subsequently, based on the calculated particle core diameters and on all available feasible compositions, provided from our discretization scheme, the composition- and size-dependent extinction cross-sections are calculated. The latter is performed by means of our proposed optical model, that is, Mie’s theory with corrections of the dielectric function.
In a first step, we confirm the functionality of our analytical method with simulated sedimentation data. This data is obtained with an own developed forward model. Our algorithm simulates gravitational sweep data at constant radial position for discrete noble metal content distributions and continuous particle size distributions. In the next step, we apply our analysis to gold-silver alloy nanoparticles synthesized by the chemical co-reduction method. For further validation, the distributions of particle size and composition are compared with the results obtained from electron microscopy and inductively coupled plasma-optical emission spectrometry. The measured and simulated 2D size-composition distributions agree very well. Our method presents great advantages in comparison to tedious SEM or TEM analysis, such as higher throughput, much better statistical significance, less human operating time, and multi-parameter resolution. The development and application of this fast and highly accurate method enables the targeted optimization of the composition and size of novel noble metal nanoparticle synthesis processes. |
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