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C: Plasmonics; Optical, Magnetic, and Hybrid Materials
Selective DNP Signal Amplification to Probe Structures of Core-Shell Polymer Hybrid Nanoparticles Timmy Schäfer, Steffen Vowinkel, Hergen Breitzke, Markus Gallei, and Torsten Gutmann J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b07969 • Publication Date (Web): 20 Dec 2018 Downloaded from http://pubs.acs.org on December 21, 2018
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The Journal of Physical Chemistry
Selective DNP Signal Amplification to Probe Structures of Core-Shell Polymer Hybrid Nanoparticles Timmy Schäfer1, Steffen Vowinkel2, Hergen Breitzke1, Markus Gallei2, Torsten Gutmann1* a Eduard-Zintl
Institute for Inorganic and Physical Chemistry, Technische Universität Darmstadt, AlarichWeiss-Str. 8, D-64287 Darmstadt, Germany b Ernst-Berl Institute for Chemical Engineering and Macromolecular Science, Technische Universität Darmstadt, Alarich-Weiss-Str. 4, D-64287 Darmstadt, Germany.
Corresponding author:
[email protected] Abstract An efficient approach for the characterization of core-shell polymer hybrid nanoparticles is presented. Selective signal amplification by dynamic nuclear polarization (DNP) is employed to shed more light on the molecular structure of surface sites and of the shell of the particles. DNP enhanced 29Si solid-state NMR is used to clearly prove the core-shell structure of the nanoparticles as well as the success of their functionalization with low amounts of trimethylsiloxy groups. By combination of DNP enhanced 1H29Si and 1H13C cross-polarization magic-angle-spinning (CP MAS) experiments, differently substituted alkoxysilane moieties, namely methacryloxypropyltriethoxysilane (MPSEt), 3methacryloxypropyltriisopropoxysilane (MPSIsoprop) and 3-methacryloxypropyltris (methoxyethoxy)silane (MPSMeEt) are investigated, revealing various crosslinking capabilities of the particle shell. This knowledge about efficiency of surface functionalization and cross-linking sites strongly influences the application and properties of the core-shell polymer hybrid particles for instance as materials for photonic crystals, particle film formation and coatings. This is of high importance for the design of tailor-made core-shell particle architectures.
Introduction Functional hybrid films provide excellent electrical, magnetic or optical properties.1-5 These films can be derived by colloidal crystallization based on particles containing typical sizes in the range of 120 – 350 nm, which are obtainable by inexpensive bottom-up approaches, leading to materials with sufficient optical performance, i.e., iridescent reflection colors caused by Bragg diffraction of visible light.6-9 In addition, such artificially generated colloidal crystals can be provided with smart functionalities leading to materials with a variety of potential applications.10 For example the functionalization with stimuliresponsive polymers results in reversibly switchable polymer opals for a variety of optical sensor applications.11-15 The so-called melt-shear organization technique allows for the formation of (hybrid) colloidal crystal films for various applications. 15-17 For this technique, a rather complex core-shell particle architecture consisting of a rigid core and a soft, elastomeric shell is required. Moreover, an interlayer connecting the soft polymer shell with the comparably hard core material is required enabling processing of the particles by for instance extrusion or compression. In general, a major challenge of 1 ACS Paragon Plus Environment
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functional hybrid films is their structural characterization at a molecular level, which is required to gain a deeper understanding of their structure-property relationship. Thus, the development of novel analytical methods that address complex polymer hybrid structures is of enormous importance with regard to a tailor-made design. Since these materials contain complex disordered structures at the nanoscale, a technique is necessary that probe local environments. Solid-state NMR spectroscopy is an important method, which in principle allows for the measurement of local interactions of functionalized materials. However, it suffers from its low intrinsic sensitivity and from its low selectivity for analyzing multicomponent materials. This is especially a disadvantage when low abundant components attached to surfaces have to be addressed. Within the present study, this is the case for functionalized polymer core-shell nanoparticles with diameters in the range of 200-300 nm. Such particles often contain only low amounts of surface functional groups whose detection by multinuclear solid-state NMR is challenging as shown in a recent work.18 Furthermore, detailed information on the structure of the shell of the particles are not accessible, since the 1H13C CP MAS NMR signals of the polymer core of the particles are dominating the spectra.19 Surface enhanced dynamic nuclear polarization (SENS-DNP) at high magnetic fields is a powerful technique to access systems with small specific surface areas (
