The interface is the crucial part in composite materials, which maybe natural or man-made. We folloed the the modifcations in inorganic fillers for the incorporation in polymer nanocomposites by <sup>27</sup>Al solid-state NMR. To study molecular dynamics in thin polymer systems like polymer brushes relaxation NMR has been combined with high-resolution solid-state NMR (CRAMPS), providing sufficient resolution to identify functional groups and to separate solvent signals in swelling experiments. This approach shows severe restrictions in the molecular dynamics in polymer brushes compared to bulk polymers.<br/>Special experiments permit the selective excitation at the interface between, the organic and the inorganic phase by frequency selection combined with a relaxation filter. In nanoparticles from hydroxyapatite the OH signal is selectively excited by a chemical-shift selective spin echo, which benefits from the narrow linewidth. Then the magnetization is spread out by a spin diffusion period. The particles had been coated by polyelectrolyte multilayers from poly(maleic anhydride-co- ethylene) and poly(diallyldimethylamonium chloride and the outermost layer from poly(styrene sulfonate) (PSS). The aromatic signal from the PSS is identified in the MAS spectrum can thus be used as a ruler to correlate the spin diffusion time with the independently measured layer thickness. After establishing the techniques on model systems, it has been applied to realistic particle-filled polymer systems and biomimetic hydroxyapatite-gelatine nanoparticles. A similar approach has been combined with solid-state DNP on spin labelled polyelectrolytes providing a localized source of the magnetization. The experiments are complemented with X-band EPR and lineshape analysis for the molecular mobility.

Structure and dynamics at interfaces in hybrid materials

253rd National Meeting (2017)

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