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Molecular Order and Dynamics in Nanostructured Materials by Solid-State NMR
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
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.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2015:7
Keyword [en]
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
Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-160636ISBN: 978-91-7595-424-0 (print)OAI: oai:DiVA.org:kth-160636DiVA: diva2:790653
Public defence
2015-03-20, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20150225

Available from: 2015-02-25 Created: 2015-02-25 Last updated: 2015-02-25Bibliographically approved
List of papers
1. Low rf power high resolution H-1-C-13-N-14 separated local field spectroscopy in lyotropic mesophases
Open this publication in new window or tab >>Low rf power high resolution H-1-C-13-N-14 separated local field spectroscopy in lyotropic mesophases
2012 (English)In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 223, 73-79 p.Article in journal (Refereed) Published
Abstract [en]

Efficiency of the proton detected (encoded) H-1-C-13-N-14 local field spectroscopy technique at low radiofrequency power is examined when applied to concentrated ionic lyotropic mesophases exhibiting heteronuclear and homonuclear dipolar couplings in kHz range. We demonstrate that highly resolved heteronuclear dipolar spectra can be obtained with limited radiofrequency power corresponding to decoupling B-1 field of 20 kHz and with superior spectral resolution and sensitivity provided by standard solution state probes. To maintain sufficiently large spectral window in indirect dimension, power level alternation scheme for homonuclear decoupling was introduced. In anisotropic mesophases of an ionic surfactant, pair-wise coupling constants in the three-spin system H-1-C-13-N-14 were accurately determined. Relative signs of heteronuclear dipolar couplings to nitrogen were obtained employing frequency selective decoupling.

Keyword
Separated local field spectroscopy, PDLF, Heteronuclear dipolar coupling, Liquid crystal
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-105666 (URN)10.1016/j.jmr.2012.07.012 (DOI)000309570600013 ()2-s2.0-84865824129 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20121129

Available from: 2012-11-29 Created: 2012-11-23 Last updated: 2017-12-07Bibliographically approved
2. Sign-sensitive determination of heteronuclear dipolar coupling to spin-1 by selective decoupling
Open this publication in new window or tab >>Sign-sensitive determination of heteronuclear dipolar coupling to spin-1 by selective decoupling
2012 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 137, no 23, 234902- p.Article in journal (Refereed) Published
Abstract [en]

This paper presents a theoretical and experimental study of nuclear magnetic resonance technique for sign-sensitive determination of the dipolar couplings of rare spins-1/2 to spin-1 with a strong quadrupolar interaction. The technique is based on low-power transition-selective single-quantum decoupling of spin-1 in the presence of high-power decoupling of abundant (proton) spins. Single-transition operator formalism is employed to calculate the time evolution of the density matrix in the presence of low-power irradiation of spin-1. Generally, the sign of dipolar coupling is unavailable from intrinsically symmetric shapes of dipolar-coupled spectra. Asymmetric dipolar multiplets, resulted from selective decoupling, reveal both the signs and magnitudes of the heteronuclear dipolar couplings. The approach is used to develop the experimental strategy for sign-sensitive measurements of short- and long-range heteronuclear dipolar couplings in highly ordered anisotropic samples. The technique is demonstrated for 13C-2H and 13C-14N spin pairs and for 13C- 2H2 three-spin system in liquid crystals.

Keyword
liquid crystals, long-range order, nuclear magnetic resonance, quadrupole coupling, short-range order, spin systems
National Category
Chemical Sciences Physical Sciences
Identifiers
urn:nbn:se:kth:diva-116657 (URN)10.1063/1.4771697 (DOI)000312780300038 ()2-s2.0-84871956006 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20130123

Available from: 2013-01-23 Created: 2013-01-22 Last updated: 2017-12-06Bibliographically approved
3. Probing Molecular Mobility in Nanostructured Composites by Heteronuclear Dipolar NMR Spectroscopy
Open this publication in new window or tab >>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
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.

Keyword
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
Identifiers
urn:nbn:se:kth:diva-158436 (URN)10.1021/jp510016z (DOI)000345891900081 ()2-s2.0-84915822388 (Scopus ID)
Note

QC 20150109

Available from: 2015-01-09 Created: 2015-01-08 Last updated: 2017-12-05Bibliographically approved
4. Chain dynamics of surfactants in mesoporous silica
Open this publication in new window or tab >>Chain dynamics of surfactants in mesoporous silica
2013 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, no 42, 18620-18626 p.Article in journal (Refereed) Published
Abstract [en]

Mesostructured porous materials possess unique surface, structural, and bulk properties that lead to important practical applications. By retaining structure-directing species in the product material, mesostructured organic-inorganic composites are obtained which are of broad interest for fundamental studies of confinement effects and surface interaction on structural and dynamic properties of organic molecules. In the present study, solid state dipolar C-13-H-1 NMR spectroscopy is applied to quantitatively characterize the conformational dynamics of organic surfactants in the mesostructured composite CTAB-MCM41. Such an approach does not require assumptions and adjustable parameters and reflects the changes in conformational dynamics without relying on specific motional models. The conformational dynamics of the surfactant confined in solid hexagonal arrays is compared to that in hexagonal aggregates formed in a concentrated aqueous solution. The study showed that in cylindrical pores of hexagonal mesoporous silica the order parameter gradually decreases towards the end of the chain. The degree of order and the order parameter profile is similar to that observed in hexagonal liquid crystalline phases. However, the mobility of segments close to the head group is more restricted compared to that in the mesophase, as the result of interaction with the solid silica interface.

Keyword
Solid-State Nmr, Heteronuclear Dipolar Couplings, Mesostructured Materials, Polarization Transfer, C-13 Nmr, Liquid-Crystals, Lipid-Bilayers, Fast Mas, Spectroscopy, Diffusion
National Category
Other Chemistry Topics
Identifiers
urn:nbn:se:kth:diva-133672 (URN)10.1039/c3cp52562g (DOI)000325728400034 ()2-s2.0-84885589136 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20131108

Available from: 2013-11-08 Created: 2013-11-08 Last updated: 2017-12-06Bibliographically approved
5. Conformational Dynamics of Surfactant in a Mesolamellar Composite Studied by Local Field NMR Spectroscopy
Open this publication in new window or tab >>Conformational Dynamics of Surfactant in a Mesolamellar Composite Studied by Local Field NMR Spectroscopy
2013 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 46, 24511-24517 p.Article in journal (Refereed) Published
Abstract [en]

Ordered mesostructured materials possess unique surface, structural, and bulk properties that lead to important practical applications. Mesostructured organic inorganic composites are also of broad interest for fundamental studies of confinement effects and surface interaction on structural and dynamic properties of organic molecules. In the present study, solid state dipolar C-13-H-1 NMR spectroscopy is applied to quantitatively characterize the conformational dynamics of a surfactant in a mesolamellar composite. By applying dipolar recoupling and separated local field spectroscopy techniques, the motion of surfactant molecules was studied in a wide range of mobilities from an essentially immobilized rigid state to a highly flexible and anistropically tumbling state. From the analysis of the measured heteronudear dipolar couplings, the orientational order parameters of C-H bonds along the surfactant chain were determined. The study shows that in surfactant bilayers in AIPO layered structure at room temperature the highly ordered chains in all-trans conformation undergo fast rotation about the molecular axis. In a higher temperature phase, the order parameter is gradually decreasing toward the chain end due to conformational transitions; however, the dynamics of the segment in the vicinity of the headgroup is only slightly affected. The conformational dynamics in the surfactant bilayers confined between solid inorganic sheets is also compared to that in fluid bilayers in an aqueous lamellar phase.

Keyword
Solid-State Nmr, Heteronuclear Dipolar Couplings, Nuclear-Magnetic-Resonance, Mesostructured Aluminophosphates, Mesoporous Silica, C-13 Nmr, Polarization Transfer, Liquid-Crystalline, Segmental Order, Lipid-Bilayers
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-138362 (URN)10.1021/jp409450j (DOI)000327557300049 ()2-s2.0-84888634355 (Scopus ID)
Note

QC 20131220

Available from: 2013-12-20 Created: 2013-12-19 Last updated: 2017-12-06Bibliographically approved
6. Phase Transitions and Chain Dynamics of Surfactants Intercalated into the Galleries of Naturally Occurring Clay Mineral Magadiite
Open this publication in new window or tab >>Phase Transitions and Chain Dynamics of Surfactants Intercalated into the Galleries of Naturally Occurring Clay Mineral Magadiite
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.

Keyword
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
Identifiers
urn:nbn:se:kth:diva-148608 (URN)10.1021/la501898x (DOI)000338806500029 ()2-s2.0-84903974295 (Scopus ID)
Note

QC 20140811

Available from: 2014-08-11 Created: 2014-08-11 Last updated: 2017-12-05Bibliographically approved

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