Incorporation of inorganic nanocrystals in polymer fibers is always a challenging process with two major requirements, i.e. the particles should be homogenously distributed in the polymer matrix and the nanomaterial properties must be kept during the processing of the fibers. These criteria become even more demanding if the final product is intended for later medical application, where the material must comply with the high safety standards. However, the incorporated total nanoparticle concentration in polymer fibers is usually very low, which implies that certification of the unaltered crystal structure of the nanomaterial cannot be achieved by conventional XRD methods. Within the present study we demonstrate that Scanning Electron Nano Diffraction (SEND) [1] in a STEM is a suitable alternative technique to XRD for handling this issue. Thus the SEND method was applied on magnetite (Fe₃O₄) nanocrystals incorporated in melt spinned polyvinylidene fluoride (PVDF) fibers for verifying the inverse spinel structure of the iron oxide particles. The diffraction experiments were carried out in a FEI Titan S/TEM @ 300 kV using ultrathin cross section samples received from ultramicrotomy on resin embedded nano magnetite loaded PVDF-fibers. Within one measuring campaign a total number of 100 diffraction patterns were recorded from sample regions ranging from 21×21 nm² to 34×41 nm² in size. Interplanar spacings and angles between the diffraction spots were determined from 12 unambiguous indexed zone axis patterns and used for verifying the structure of magnetite and for calculation of the cubic lattice parameter. Hence evaluation of 90 unique indexed interplanar spacings in the range between 4.8 Å and 1.0 Å yielded a lattice parameter of a = 8.36(9) Å for the cubic unit cell with Fd-3m symmetry. 

References:

[1] J.M. Zou and J. Tao, Scanning Electron Nanodiffraction and Diffraction Imaging in Scanning Transmission Electron Microscopy – Imaging and Analysis, Springer Science+Buisness Media, pp. 393–427, 2011.

Figures:

Scanning Electron Nano Diffraction (SEND) patterns in (a) and corresponding simulated electron diffraction patterns for nano-magnetite in (b). The frame colors refer to the position of the electron beam during acquisition of the diffraction patterns.

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EMC Abstracts - https://emc-proceedings.com/abstract/structural-verification-of-magnetite-nanocrystals-in-pvdf-fibers-by-scanning-electron-nano-diffraction-send/