Probing Molecular Mobility in Nanostructured Composites by Heteronuclear Dipolar NMR Spectroscopy
2014 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 48, 28308-28313 p.Article in journal (Refereed) Published
Conformational and reorientational dynamics of surfactant molecules confined within solid inorganic frameworks of nanostructured composites are studied by solid-state NMR. Since the organic part in the nanocomposites exhibits a great variation in the local molecular mobility, a significant challenge in these materials is to develop an experimental method efficient both for nearly immobilized and for highly dynamic flexible molecules. We introduce a dipolar recoupling NMR technique to study local molecular motion via heteronuclear dipolar spin interactions in a wide range of coupling constant values. The approach is efficient in both rigid and mobile molecules. The method is applied to ordered nanostructured composites to obtain model-independent information on the local molecular dynamics. On the basis of experimentally determined local order parameters of the molecular segments, we put forward physical models for the motion of surfactant molecules in nanoconfined assemblies. In composites with lamellar structure, the hydrocarbon chains adopt well-ordered essentially all-trans conformations and, depending on sample composition, undergo either small-angle wobbling or free rotation around the long molecular axes. In contrast, surfactant molecules in hexagonal mesoporous silica exhibit highly dynamic conformationally disordered chains.
Place, publisher, year, edition, pages
2014. Vol. 118, no 48, 28308-28313 p.
Chains, Mesoporous materials, Molecular dynamics, Molecules, Nanocomposites, Nuclear magnetic resonance spectroscopy, Surface active agents, Dipolar recoupling, Experimental methods, Flexible molecules, Hexagonal mesoporous silica, Nanostructured composites, Reorientational dynamics, Surfactant molecules, Trans conformations
IdentifiersURN: urn:nbn:se:kth:diva-158436DOI: 10.1021/jp510016zISI: 000345891900081ScopusID: 2-s2.0-84915822388OAI: oai:DiVA.org:kth-158436DiVA: diva2:777854
QC 201501092015-01-092015-01-082015-02-25Bibliographically approved