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Phase Transitions and Chain Dynamics of Surfactants Intercalated into the Galleries of Naturally Occurring Clay Mineral Magadiite
KTH, School of Chemical Science and Engineering (CHE), Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.ORCID iD: 0000-0002-6524-1441
2014 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 30, no 26, 7859-7866 p.Article in journal (Refereed) Published
Abstract [en]

We investigate conformational dynamics and phase transitions of surfactant molecules confined in the layered galleries of the organo-modified, natural polysilicate clay, magadiite. We have shown that our approach to studying this class of materials is capable of delivering detailed information on the molecular mobility of the confined molecules. From the analysis of the measured heteronuclear dipolar couplings, the orientational order parameters of the C-H bonds along the hydrocarbon chain have been determined. Three phases have been observed in the nanocomposite, characterized by distinct dynamical states of the surfactant. At room temperature, restricted mobility of the molecules led to the adoption of an essentially all-trans conformation by the chains. This behavior can be described by a model incorporating small-angle wobbling around the long molecular axes of the chains. Upon heating, dynamic transformation takes place, resulting in a rotator type solid phase where molecules in extended all-trans conformations undergo fast and unrestricted rotation about their respective symmetry axes. The second phase transition is associated with chain melting and the onset of translational dynamics and results in an essentially liquid-crystalline-like state of the organic component. The mobility of the surfactant is one of the key factors facilitating the efficient penetration of macromolecules in the process of preparing of polymer/organoclay nanocomposites. The exploration of dynamic properties of the fimctionalizing organic layer should provide important input into the improved design of new organic-inorganic hybrid materials.

Place, publisher, year, edition, pages
2014. Vol. 30, no 26, 7859-7866 p.
Keyword [en]
Conformational dynamics, Dynamic transformation, Heteronuclear dipolar couplings, Organic-inorganic hybrid materials, Orientational order parameters, Restricted mobilities, Surfactant molecules, Translational dynamics, Chains, Dynamics, Hybrid materials, Molecules, Nanocomposites, Surface active agents
National Category
Chemical Sciences
URN: urn:nbn:se:kth:diva-148608DOI: 10.1021/la501898xISI: 000338806500029ScopusID: 2-s2.0-84903974295OAI: diva2:737075

QC 20140811

Available from: 2014-08-11 Created: 2014-08-11 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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