|441. Polzer, F.; Holub-Krappe, E.; Rossner, H.; Erko, A.; Kirmse, H.; Plamper, F.A.; Schmalz, A.; Müller, A.H.E.; Ballauff, M.: Structural Analysis of Composites of MnOx and a Polymer Colloid, Coll. Polym. Sci. 291, 469 – 481 (2013) -- DOI: 10.1007/s00396-012-2725-8|
We report on the detailed structure of MnOx nanoparticles (MnOxNP) which are either stabilized by cationic spherical polyelectrolyte brushes or by star-shaped cationic polyelectrolyte chains. In both cases, the polycation is composed of 2-(trimethylammonium)ethyl methacrylate chloride (TMAEMC). The analysis by transmission electron microscopy (TEM), cryogenic transmission electron microscopy (cryoTEM) and powder X-ray diffraction (PXRD) leads to the conclusion that the MnOx nanoparticles in aqueous dispersed state are composed of only a few or even single lamellae of c-disordered potassium birnessite (birnessite). Using star-shaped pTMAEMC homopolymer for the synthesis of composite particles we obtain MnOxNP with an average diameter of about 5 nm. MnOxNP immobilized on cationic spherical polyelectrolyte brush (SPB) have a length of about 20 nm and a width of 1.6 nm. Comparison of the extended X-ray absorption fine structure (EXAFS) spectra of the MnOx composites with reference spectra leads to the conclusion that all materials include c-disordered birnessite-type nanoparticles. A comparison of the energy shift of the Mn K edge absorption peak of the X-ray absorption near edge structure (XANES) spectra of different manganese oxide reference materials with the different MnOxNP revealed an average oxidation state of about 3.5-3.7 for synthesized compounds. No distinct structural difference is found when comparing the dried samples to samples dispersed in water. A comparison of the EXAFS data of the birnessite nanoparticles with the crystal structure of macroscopic systems showed a compression along the c-direction accompanied by a slight elongation within the ab-plane of the layered material.