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

Anja Müller, Thomas Heinrich, Sven Tougaard, Wolfgang S.M. Werner, Martin Hronek, Valentin Kunz, Jörg Radnik, Jörg M. Stockmann, Vasile Dan Hodoroaba, Sigrid Benemann, Nithiya Nirmalananthan-Budau, Daniel Geißler, Katia Sparnacci, Wolfgang E.S. Unger*

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

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Abstract

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 (T-SEM), 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 (ToF-SIMS) 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.

Original languageEnglish
JournalJournal of Physical Chemistry C
Volume123
Issue number49
Pages (from-to)29765-29775
Number of pages11
ISSN1932-7447
DOIs
Publication statusPublished - 12. Nov 2019

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