Journal Article

FZJ-2015-01765

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Structure and Dynamics of Octamethyl-POSS Nanoparticles

Jalarvo, N. (Corresponding Author)FZJ* ; Gourdon, O. ; Ehlers, G. ; Tyagi, M. ; Kumar, S. K. ; Dobbs, K. D. ; Smalley, R. J. ; Guise, W. E. ; Ramirez-Cuesta, A. ; Wildgruber, C. ; Crawford, M. K.

2014
Soc. Washington, DC

This record in other databases:    

Please use a persistent id in citations: doi:10.1021/jp412228r

Abstract: Polyoligosilsesquioxanes (POSS) are a large family of Si–O cage molecules that have diameters of 1–2 nm and can be viewed as perfectly monodisperse silica nanoparticles. POSS can be synthesized with a wide variety of functional ligands attached to their surfaces. Here we report the results of a comprehensive study of the crystal structure and ligand dynamics of one of the simplest POSS nanoparticles, octamethyl-POSS or Si8O12(CH3)8, where the central Si8O12 cage is surrounded by eight methyl ligands. Neutron powder diffraction data highlight the presence of strongly temperature-dependent methyl group rotational dynamics. Vibrational spectra were measured using Raman and inelastic neutron scattering techniques, and the results of the measurements were compared with the predictions of density functional theory calculations. In particular, the inelastic neutron scattering spectra show the fundamental and first overtone transitions of the methyl torsional vibrations; these transitions are forbidden in both Raman and infrared spectroscopy for the molecule with its ideal octahedral symmetry. The energies of these transitions are used to determine the height of the torsional energy barrier. Direct measurements of the methyl group dynamics using quasielastic incoherent neutron scattering provide the hydrogen atom jump distance and the activation energy for rotation of the methyl groups. Together these results provide a detailed picture of the structure and ligand dynamics of this POSS molecule.

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Contributing Institute(s):

1. Neutronenstreuung (Neutronenstreuung ; JCNS-1)
2. JCNS-SNS (JCNS-SNS)

Research Program(s):

1. 54G - JCNS (POF2-54G24) (POF2-54G24)
2. 451 - Soft Matter Composites (POF2-451) (POF2-451)

Appears in the scientific report 2014

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Database coverage:
; Current Contents - Physical, Chemical and Earth Sciences ; IF < 5 ; JCR ; SCOPUS ; Science Citation Index ; Science Citation Index Expanded ; Thomson Reuters Master Journal List ; Web of Science Core Collection

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