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Probing Molecular Mobility in Nanostructured Composites by Heteronuclear Dipolar NMR Spectroscopy
KTH, School of Chemical Science and Engineering (CHE), Chemistry. St. Petersburg State University, Russian Federation .
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry. St. Petersburg State University, Russian Federation.ORCID iD: 0000-0002-6524-1441
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
Abstract [en]

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.
Keyword [en]
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
National Category
Chemical Sciences
URN: urn:nbn:se:kth:diva-158436DOI: 10.1021/jp510016zISI: 000345891900081ScopusID: 2-s2.0-84915822388OAI: diva2:777854

QC 20150109

Available from: 2015-01-09 Created: 2015-01-08 Last updated: 2015-02-25Bibliographically approved
In thesis
1. Molecular Order and Dynamics in Nanostructured Materials by Solid-State NMR
Open this publication in new window or tab >>Molecular Order and Dynamics in Nanostructured Materials by Solid-State NMR
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Organic-inorganic nanostructured composites are nowadays integrated in the field of material science and technology. They are used as advanced materials directly or as precursors to novel composites with potential applications in optics, mechanics, energy, catalysis and medicine. Many properties of these complex materials depend on conformational rearrangements in their inherently dynamic organic parts. The focus of this thesis is on the study of the molecular mobility in ordered nanostructured composites and lyotropic mesophases and also on the development of relevant solid-state NMR methodologies.

In this work, a number of new experimental approaches were proposed for dipolar NMR spectroscopy for characterizing molecular dynamics with atomic-level resolution in complex solids and liquids. A new acquisition scheme for two-dimensional dipolar spectroscopy has been developed in order to expand the spectral window in the indirect dimension while using limited radio-frequency power. Selective decoupling of spin-1 nuclei for sign-sensitive determination of the heteronuclear dipolar coupling has been described. A new dipolar recoupling technique for rotating samples has been developed to achieve high dipolar resolution in a wide range of dipolar coupling strength. The experimental techniques developed herein are capable of delivering detailed model-independent information on molecular motional parameters that can be directly compared in different composites and their bulk analogs.

Solid-state NMR has been applied to study the local molecular dynamics of surfactant molecules in nanostructured organic-inorganic composites of different morphologies. On the basis of the experimental profiles of local order parameters, physical motional models for the confined surfactant molecules were put forward. In layered materials, a number of motional modes of surfactant molecules were observed depending on sample composition. These modes ranged from essentially immobilized rigid states to highly flexible and anisotropically tumbling states. In ordered hexagonal silica, highly dynamic conformationally disordered chains with restricted motion of the segments close to the head group have been found.

The results presented in this thesis provide a step towards the comprehensive characterization of the molecular states and understanding the great variability of the molecular assemblies in advanced nanostructured organic−inorganic composite materials.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. 54 p.
TRITA-CHE-Report, ISSN 1654-1081 ; 2015:7
mesoporous materials, organic-inorganic nanocomposites, surfactants, liquid crystals, MCM-41, clays, conformational dynamics, solid-state NMR, local field spectroscopy, dipolar coupling, dipolar recoupling, spin decoupling.
National Category
Physical Chemistry
Research subject
urn:nbn:se:kth:diva-160636 (URN)978-91-7595-424-0 (ISBN)
Public defence
2015-03-20, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)

QC 20150225

Available from: 2015-02-25 Created: 2015-02-25 Last updated: 2015-02-25Bibliographically approved

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Kharkov, Boris B.Dvinskikh, Sergey V.
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