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A structural investigation into the complexity of mesoporous silica crystals: From a view of curvature and micellar interaction to quasicrystallinity
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
##### Abstract [en]

Mesoporous silica crystals have a large variety of structures mainly due to the versatility of their structure template. The configuration and the chemical state of the templating micellar surfactants, together with the kinetic process of silica will determine the final outcome of the synthesis. Increasing the understanding of the complex formation processes involved will enable a possibilityto fine tune the material for specific uses, today focused into the fields of photoniccrystals, drug delivery, catalysis and separation technology.

In this thesis emphasis is put on (1) increasing the understanding the formation mechanism yielding the different species of mesoporous silica crystals through an in depth study of quasicrystallinity (2) Characterization and description of the structural complexity through various characterization techniquesand also by studying the kinetic structural transformation phenomenon related to the minimal G- and D-surfaces. (3) The structural studies of the versatile surfactant liquid crystals for establishing a thermodynamically stable basis to evaluate the kinetic mesoporous silica growth processes. Furthermorethe thesis both enlightens the possibilities of and contributes to the developmentof electron microscopy characterization techniques.

In these studies, electron microscopy is largely employed in the characterization to give a thorough picture of the mesoporous structures. This is combined with the sample preparation techniques cross-section polishing and ionslicing. Low voltage scanning electron microscopy is utilized for studying the surfaces and cross-sections of various materials at the limit of the resolution. Here, a deep understanding of the electron beam-material interaction is used for a better interpretation of the detected signals. Transmission electron microscopyis combined with electron crystallographic reconstruction to yield a three dimensional structural model. For determination of the quasicrystallinity level for a structure of dodecagonal tiling, revealed in the scope of this study,a phason strain analysis was made.

##### Place, publisher, year, edition, pages
Stockholm: Department of Materials and Environmental Chemistry (MMK), Stockholm University , 2012. , p. 110
##### Keyword [en]
electron microscopy, mesoporous silica, quasicrystal, minimal surface
##### National Category
Chemical Sciences
##### Research subject
Structural Chemistry
##### Identifiers
ISBN: 978-91-7447-602-6 (print)OAI: oai:DiVA.org:su-82382DiVA, id: diva2:567504
##### Public defence
2012-12-21, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 13:30 (English)
##### Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 7: Manuscript.

Available from: 2012-11-29 Created: 2012-11-13 Last updated: 2012-11-20Bibliographically approved
##### List of papers
1. Dodecagonal tiling in mesoporous silica
Open this publication in new window or tab >>Dodecagonal tiling in mesoporous silica
2012 (English)In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 487, no 7407, p. 349-353Article in journal (Refereed) Published
##### Abstract [en]

Recent advances in the fabrication of quasicrystals in soft matter systems have increased the length scales for quasicrystals(1) into the mesoscale range (20 to 500 angstroms). Thus far, dendritic liquid crystals(2), ABC-star polymers(3), colloids(4) and inorganic nanoparticles(5) have been reported to yield quasicrystals. These quasicrystals offer larger length scales than intermetallic quasicrystals (a few angstroms)(1,6), thus potentially leading to optical applications through the realization of a complete photonic bandgap induced via multiple scattering of light waves in virtually all directions(7-9). However, the materials remain far from structurally ideal, in contrast to their intermetallic counterparts, and fine control over the structure through a self-organization process has yet to be attained. Here we use the well-established self-assembly of surfactant micelles to produce a new class of mesoporous silicas, which exhibit 12-fold (dodecagonal) symmetry in both electron diffraction and morphology. Each particle reveals, in the 12-fold cross-section, an analogue of dodecagonal quasicrystals in the centre surrounded by 12 fans of crystalline domains in the peripheral part. The quasicrystallinity has been verified by selected-area electron diffraction and quantitative phason strain analyses on transmission electron microscope images obtained from the central region. We argue that the structure forms through a non-equilibrium growth process, wherein the competition between different micellar configurations has a central role in tuning the structure. A simple theoretical model successfully reproduces the observed features and thus establishes a link between the formation process and the resulting structure.

##### National Category
Chemical Sciences
##### Research subject
Structural Chemistry
##### Identifiers
urn:nbn:se:su:diva-80284 (URN)10.1038/nature11230 (DOI)000306506500039 ()
##### Note

AuthorCount:5;

Available from: 2012-09-26 Created: 2012-09-17 Last updated: 2017-12-07Bibliographically approved
2. Bicontinuous Cubic Mesoporous Materials with Biphasic Structures
Open this publication in new window or tab >>Bicontinuous Cubic Mesoporous Materials with Biphasic Structures
2011 (English)In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 17, no 48, p. 13510-13516Article in journal (Refereed) Published
##### Abstract [en]

The replication of amphiphilic systems within an inorganic silica matrix allows the study of the fundamental properties of mesostructural changes, that is, kinetic and structural parameters. Herein we report a detailed study of the transition between cubic bicontinuous mesostructure with space groups Ia$\bar 3$d and Pn$\bar 3$m symmetry, which are associated with the minimal G and D surfaces, respectively. The transition may be induced through micellar swelling of the anionic amphiphilic surfactant N-lauroyl alanine by trimethylbenzene. Rich kinetic behaviour is observed and has been exploited to prepare particles with biphasic structures. Transmission electron microscopy evidence indicates that there is epitaxial growth from one mesostructure to the other involving the [111] and [110] orientations of the Ia$\bar 3$d and Pn$\bar 3$m symmetry structures, respectively. From kinetic studies, we show that the formation of the Ia$\bar 3$d mesophase is preceded by a hexagonal phase (plane group p6mm) and an epitaxial relationship has been observed involving the sixfold or $\bar 3$ axis orientations of both structures. Our data suggests that the Pn$\bar 3$m mesostructure is kinetically stable at low temperatures whereas the Ia$\bar 3$d mesostructure is the more stable structure after prolonged periods of hydrothermal treatment. We present evidence from transmission electron microscopy and small-angle X-ray diffractograms and also electron crystallography modelling of the unit cells at particular points in the structural change.

##### Keyword
bicontinuous structures, epitaxial growth, liquid crystals, mesoporous materials
##### National Category
Chemical Sciences
##### Research subject
Structural Chemistry
##### Identifiers
urn:nbn:se:su:diva-82372 (URN)10.1002/chem.201101831 (DOI)000298059600019 ()
Available from: 2012-11-13 Created: 2012-11-13 Last updated: 2017-12-07Bibliographically approved
3. Mesopore generation by organosilane surfactant during LTA zeolite crystallization investigated by high-resolution SEM and Monte Carlo simulation
Open this publication in new window or tab >>Mesopore generation by organosilane surfactant during LTA zeolite crystallization investigated by high-resolution SEM and Monte Carlo simulation
2011 (English)In: Solid State Sciences, ISSN 1293-2558, E-ISSN 1873-3085, Vol. 13, no 4, p. 750-756Article in journal (Refereed) Published
##### Abstract [en]

The crystallization of LTA zeolite under a hydrothermal synthesis condition that contained a quaternary ammonium-type organosilane surfactant was studied with X-ray powder diffraction (XRD), high-resolution scanning electron microscopy (HRSEM) and Monte Carlo simulation of the crystal growth. The hydrothermal reaction products were collected at various crystallization times, and investigated with XRD and HRSEM. The HRSEM images of the final zeolite products were taken as synthesized and also after cross-sectioning with an argon ion beam. The HRSEM investigation revealed presence of a disordered network of mesoporous channels that penetrated the microporous zeolite crystal. Unless the loading of the surfactant was exceedingly high, the microporous zeolite particles exhibited truncated cubic morphologies that were almost like single crystals, despite penetration by the mesopores. The outline of the zeolite particle became progressively rounded as the mesoporosity was increased according to the surfactant loading. The mesoporosity in the zeolite crystals was well maintained against crystal-ripening processes for 6 d. This result supports the fact that the organosilane surfactant micelles became incorporated inside the zeolite crystal as a mesopore generator during the crystallization process. Data from Monte Carlo simulation agreed with these experimental results.

##### Keyword
Mesoporous zeolite, Hierarchical zeolite, Zeolite LTA, Organosilane surfactant, Mesopore-generating agent, High resolution SEM, Cross-section polishing technique
##### National Category
Chemical Sciences
##### Research subject
Materials Chemistry; Structural Chemistry
##### Identifiers
urn:nbn:se:su:diva-55035 (URN)10.1016/j.solidstatesciences.2010.04.022 (DOI)000289965900011 ()
Available from: 2011-02-25 Created: 2011-02-25 Last updated: 2017-12-11Bibliographically approved
4. Cracking mechanisms of clay-based and GCC-based coatings
Open this publication in new window or tab >>Cracking mechanisms of clay-based and GCC-based coatings
2011 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 26, no 4, p. 485-492Article in journal (Refereed) Published
##### Abstract [en]

A new method to produce SEM cross sections was used to analyze coated and creased samples. It was found that the binder surrounded the smaller particles leaving the large pores around the larger pigment particles. Consequently, cracks would propagate next to the large particles, and at least one crack area also showed a clear pigment surface, indicating an adhesive failure between the binder and the pigment particles. GCC and clay showed different cracking directions. GCC-based coatings showed cracks that had been initiated at the surface of the coating layer and then went through the thickness direction of the coating layer. The clay-based coatings on the other hand showed cracks that could be initiated anywhere in the thickness direction in the coating layer and then continued at an angle in the thickness direction. The cracking behaviour of the clay based coatings was probably due to anisotropic mechanical properties combined with shear stresses or out-of-plane tensile stresses during creasing.

##### Keyword
Binder, Coating, Cracking, Creasing, Folding, Pigment, Latex, Starch, Electron microscopy
##### National Category
Chemical Sciences
##### Research subject
Structural Chemistry
##### Identifiers
urn:nbn:se:su:diva-82374 (URN)10.3183/NPPRJ-2011-26-04-p485-492 (DOI)000298868000016 ()
Available from: 2012-11-13 Created: 2012-11-13 Last updated: 2017-12-07Bibliographically approved
5. A novel SEM cross-section analysis of paper coating for separation of latex from void volume
Open this publication in new window or tab >>A novel SEM cross-section analysis of paper coating for separation of latex from void volume
2010 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 25, no 1, p. 107-113Article in journal (Refereed) Published
##### Abstract [en]

Coatings prepared in the laboratory and on a pilot coater have been subjected to a SEM cross-sectional analysis without applying an embedding resin. The cross-sectioning was carried out using argon ion beam etching after the coated paper had been stabilized by a resin film and a nano-layer of gold particles had been sputtered on the coated side of the paper to enhance the conductivity of it under SEM. The image quality was excellent. Pigment, latex and voids/pores were clearly seen and subjected to image analysis to give porosity and pore size distribution. The results were compared to the pore structure obtained from mercury porosimetry using the same coating formulation laid on a plastic base. Both the images and the image analysis showed significant deviations from mercury intrusion characterization.

##### Keyword
Coating, Coated paper, Ink, Printing, SEM, Cross-section, Latex, Mercury porosimetry
##### National Category
Chemical Sciences
##### Research subject
Structural Chemistry
##### Identifiers
urn:nbn:se:su:diva-50662 (URN)10.3183/NPPRJ-2010-25-01-p107-113 (DOI)000278043500014 ()
##### Note

authorCount :4

Available from: 2011-01-04 Created: 2010-12-30 Last updated: 2017-12-11Bibliographically approved
6. An Appraisal of High Resolution Scanning Electron Microscopy Applied To Porous Materials
Open this publication in new window or tab >>An Appraisal of High Resolution Scanning Electron Microscopy Applied To Porous Materials
2009 (English)In: JEOL News, Vol. 44, no 1, p. 17-22Article in journal (Refereed) Published
##### Abstract [en]

Nanoporous materials such as zeolites and mesoporous silica crystals have attracted a lot of attention in recent years. In particular, the incorporation of various materials such as organic molecules, or metal nanoparticles and other inorganic compounds within their pores which give rise to fascinating new functions. For such materials, it is essential to determine their structure, composition and mechanisms of growth in order to maximize their utility in future applications.

Recent progress in the performance of SEM is enormous, especially in low energy imaging where we can now directly observe fine surface structures of porous materials even those that are electrical insulators. Furthermore, by precise filtration and detection of emitted electrons by their energy, we can selectively obtain different types of information such as material composition, location of particles inside or outside the pores etc. The physical processes and technologies behind this precise tuning of landing and detection energies for both impact and emitted electrons, respectively, are explained and illustrated using a number of porous materials including zeolite LTA, SBA-15, SBA-16, zeolite LTL, FDU-16 and Au@TiO2 ' rattle spheres,' along with comparisons with other techniques such as atomic force microscopy (AFM) and transmission electron microscopy (TEM). We conclude that, by using extremely low landing energies, advanced sample preparation techniques and through a thorough understanding of the physical processes involved, HRSEM is providing new and unique information and perspectives on these industrially important materials.

##### National Category
Chemical Sciences
##### Research subject
Inorganic Chemistry; Structural Chemistry
##### Identifiers
urn:nbn:se:su:diva-36800 (URN)
##### Note

Totalt antal författare 17 st.

Available from: 2010-01-27 Created: 2010-01-26 Last updated: 2012-11-20Bibliographically approved
7. Structures of the C14GlutANa surfactant liquid crystals
Open this publication in new window or tab >>Structures of the C14GlutANa surfactant liquid crystals
##### National Category
Chemical Sciences
##### Research subject
Structural Chemistry
##### Identifiers
urn:nbn:se:su:diva-82380 (URN)
Available from: 2012-11-13 Created: 2012-11-13 Last updated: 2012-11-20Bibliographically approved

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Cite
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