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A. Müller, T. Heinrich, S. Tougaard, W.S.M. Werner, M. Hronek, V. Kunz, J. Radnik, J. Stockmann, V. Hodoroaba, S. Benemann, N. Nirmalananthan-Budau, D. Geißler, K. Sparnacci, W. Unger:
"Determining the Thickness and Completeness of the Shell of Polymer Core−Shell Nanoparticles by X‑ray Photoelectron Spectroscopy, Secondary Ion Mass Spectrometry, and Transmission Scanning Electron Microscopy";
The Journal of Physical Chemistry C, 123 (2019), 49; 29765 - 29775.

Core−shell nanoparticles (CSNPs) have become indispensable in
various industrial applications. However, their real internal structure usually
deviates from an ideal core−shell structure. To control how the particles perform
with regard to their specific applications, characterization techniques are required
that can distinguish an ideal from a nonideal morphology. In this work, we
investigated poly(tetrafluoroethylene)−poly(methyl methacrylate) (PTFE−
PMMA) and poly(tetrafluoroethylene)−polystyrene (PTFE−PS) polymer
CSNPs with a constant core diameter (45 nm) but varying shell thicknesses
(4−50 nm). As confirmed by transmission scanning electron microscopy (TSEM),
the shell completely covers the core for the PTFE−PMMA nanoparticles, while the encapsulation of the core by the shell
material is incomplete for the PTFE−PS nanoparticles. X-ray photoelectron spectroscopy (XPS) was applied to determine the
shell thickness of the nanoparticles. The software SESSA v2.0 was used to analyze the intensities of the elastic peaks, and the
QUASES software package was employed to evaluate the shape of the inelastic background in the XPS survey spectra. For the
first time, nanoparticle shell thicknesses are presented, which are exclusively based on the analysis of the XPS inelastic
background. Furthermore, principal component analysis (PCA)-assisted time-of-flight secondary-ion mass spectrometry (ToFSIMS)
of the PTFE−PS nanoparticle sample set revealed a systematic variation among the samples and, thus, confirmed the
incomplete encapsulation of the core by the shell material. As opposed to that, no variation is observed in the PCA score plots
of the PTFE−PMMA nanoparticle sample set. Consequently, the complete coverage of the core by the shell material is proved
by ToF-SIMS with a certainty that cannot be achieved by XPS and T-SEM.

http://dx.doi.org/10.1021/acs.jpcc.9b09258