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  • 1. Alfonso E., Garcia-Bennett
    et al.
    Xiao, Changhong
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Chunfang, Zhou
    Toen, Castle
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Keiichi, Miyasaka
    Osamu, Terasaki
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bicontinuous Cubic Mesoporous Materials with Biphasic Structures2011In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 17, no 48, p. 13510-13516Article in journal (Refereed)
    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.

  • 2. Cho, Kanghee
    et al.
    Ryoo, Ryong
    Asahina, Shunsuke
    Xiao, Changhong
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Klingstedt, Miia
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Umemura, Ayako
    Anderson, Michael W.
    Terasaki, Osamu
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Mesopore generation by organosilane surfactant during LTA zeolite crystallization investigated by high-resolution SEM and Monte Carlo simulation2011In: Solid State Sciences, ISSN 1293-2558, E-ISSN 1873-3085, Vol. 13, no 4, p. 750-756Article in journal (Refereed)
    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.

  • 3. Han, Lu
    et al.
    Ohsuna, Tetsu
    Liu, Zheng
    Alfredsson, Viveka
    Kjellman, Tomas
    Asahina, Shunsuke
    Suga, Mitsuo
    Ma, Yanhang
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Oleynikov, Peter
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Miyasaka, Keiichi
    Mayoral, Alvaro
    Diaz, Isabel
    Sakamoto, Yasuhiro
    Stevens, Sam M.
    Anderson, Michael W.
    Xiao, Changhong
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Fujita, Nobuhisa
    Garcia-Bennett, Alfonso
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Yoon, Kyung Byung
    Che, Shunai
    Terasaki, Osamu
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Korea Advanced Institute of Science & Technology (KAIST), South Korea.
    Silica-Based Nanoporous Materials2014In: Zeitschrift für Anorganische und Allgemeines Chemie, ISSN 0044-2313, E-ISSN 1521-3749, Vol. 640, no 3-4, p. 521-536Article, review/survey (Refereed)
    Abstract [en]

    Ordered nanoporous structures are among the most fascinating and industrially important materials currently in use. The archetypal zeolite material has now been joined by an eclectic array of new structures that exhibit porosity over a wide range of length scales and with order/disorder expressed in a multitude of ways. This raises the bar in terms of characterization and extends a real challenge to the scientific community to fully understand the properties and potential future applications of such materials. In this review we discuss the importance of modern microscopy tools combined with diffraction in this endeavour and show how the details of even the most complex quasi-crystalline nanoporous architectures can be elucidated. We show by using the appropriate spherical aberration (C-s) corrections in scanning transmission electron microscopy it is possible to decipher all the individual silicon and aluminum atoms in a zeolite structure. Automated routines for using large electron diffraction datasets for crystal structure determination of nanocrystals is described making the need for large single crystal synthesis less-and-less important. The power of complementary combinations of surface tools such as atomic force microscopy and high-resolution scanning electron microscopy is discussed to elucidate crystal growth mechanisms. For mesoporous materials synthesized from self-organized organic mesophases electron microscopy reveals the details of the complex hierarchy of porosity so crucial for the functional performance of the structure.

  • 4.
    Lin, C.
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Xiao, Changhong
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Shen, Zhijian James
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Nano Pores Evolution in Hydroxyapatite Microsphere during Spark Plasma Sintering2011In: Science of Sintering, ISSN 0350-820X, Vol. 43, no 1, p. 39-46Article in journal (Refereed)
    Abstract [en]

    Micron-spherical granules of hydroxyapatite (HAp) nanoparticles were prepared by powder granulation methods. Through subsequent sintering, porous HAp microspheres with tailored pore and grain framework structures were obtained. Detailed microstructure investigation by SEM and TEM revealed the correlation of the pore structure and the necking strength with the sintering profiles that determine the coalescence features of the nanoparticles. The partially sintered porous HAp microspheres containing more than 50% porosity consisting of pores and grains both in nano-scale are active in inducing the precipitation of HAp in simulated body fluid. The nano-porous HAp microspheres with an extensive surface and interconnecting pores thus demonstrate the potential of stimulating the formation of collagen and bone and the integration with the newly formed bones during physiological bone remodeling.

  • 5. Liu, Zheng
    et al.
    Fujita, Nobuhisa
    Miyasaka, Keiichi
    Han, Lu
    Stevens, Sam M.
    Suga, Mitsuo
    Asahina, Shunsuke
    Slater, Ben
    Xiao, Changhong
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Sakamoto, Yasuhiro
    Anderson, Michael W.
    Ryoo, Ryong
    Terasaki, Osamu
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Korea Advanced Institute of Science & Technology (KAIST) .
    A review of fine structures of nanoporous materials as evidenced by microscopic methods2013In: Microscopy, ISSN 2050-5698, Vol. 62, no 1, p. 109-146Article, review/survey (Refereed)
    Abstract [en]

    This paper reviews diverse capabilities offered by modern electron microscopy techniques in studying fine structures of nanoporous crystals such as zeolites, silica mesoporous crystals, metal organic frameworks and yolk-shell materials. For the case of silica mesoporous crystals, new approaches that have been developed recently to determine the three-dimensionally periodic average structure, e. g., through self-consistent analysis of electron microscope images or through consideration of accidental extinctions, are presented. Various structural deviations in nanoporous materials from their average structures including intergrowth, surface termination, incommensurate modulation, quasicrystal and defects are demonstrated. Ibidem observations of the scanning electron microscope and atomic force microscope give information about the zeolite-crystal-growth mechanism, and an energy for unstitching a building-unit from a crystal surface is directly observed by an anatomic force microscope. It is argued how these observations lead to a deeper understanding of the materials.

  • 6. Miyasaka, Keiichi
    et al.
    Bennett, Alfonso Garcia
    Han, Lu
    Han, Yu
    Xiao, Changhong
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Fujita, Nobuhisa
    Castle, Toen
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Sakamoto, Yasuhiro
    Che, Shunai
    Terasaki, Osamu
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    The role of curvature in silica mesoporous crystals2012In: INTERFACE FOCUS, ISSN 2042-8898, Vol. 2, no 5, p. 634-644Article in journal (Refereed)
    Abstract [en]

    Silica mesoporous crystals (SMCs) offer a unique opportunity to study micellar mesophases. Replication of non-equilibrium mesophases into porous silica structures allows the characterization of surfactant phases under a variety of chemical and physical perturbations, through methods not typically accessible to liquid crystal chemists. A poignant example is the use of electron microscopy and crystallography, as discussed herein, for the purpose of determining the fundamental role of amphiphile curvature, namely mean curvature and Gaussian curvature, which have been extensively studied in various fields such as polymer, liquid crystal, biological membrane, etc. The present work aims to highlight some current studies devoted to the interface curvature on SMCs, in which electron microscopy and electron crystallography (EC) are used to understand the geometry of silica wall surface in bicontinuous and cage-type mesostructures through the investigation of electrostatic potential maps. Additionally, we show that by altering the synthesis conditions during the preparation of SMCs, it is possible to isolate particles during micellar mesophase transformations in the cubic bicontinuous system, allowing us to view and study epitaxial relations under the specific synthesis conditions. By studying the relationship between mesoporous structure, interface curvature and micellar mesophases using electron microscopy and EC, we hope to bring new insights into the formation mechanism of these unique materials but also contribute a new way of understanding periodic liquid crystal systems.

  • 7.
    Qian, Bin
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Forraiová, Lenka
    Institute of Materials Research of the Slovak Academy of Sciences.
    Saeidi, Kamran
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Changhong, Xiao
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Mazaheri, Mehdi
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Zhong, Yuan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Lofaj, František
    bInstitute of Materials Research of the Slovak Academy of Sciences.
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Defect-tolerant characteristics of laser sintered CoCrMo alloy ensured by strong structural hierarchiesManuscript (preprint) (Other academic)
    Abstract [en]

    Laser sintering of a CoCrMo alloy have been found to introduce intergrown structural features on several length scales from nano- to macro-levels, i.e. structural hierarchies. The quenching of the small laser formed melting pool, when the laser focus spot moves away, will preserve high temperature phases or microstructures. A micron-sized cellular microstructure will form with Mo being enriched in a nanometer thin zone at the cell boundaries and carbide formation is suppressed. Clusters of elongated cells (crystallites) join along one common crystal structure direction forming larger up to 100 µm bundles and these grow in different intercrossing directions in the microstructure. The interlocked framework prohibits mechanical creep or deformation by sliding along weak structure planes and consumes the energy of a propagating crack. A macro-scale “weld line” structure can be formed in 3-dimensions by the bottom-up approach; the sintering of layer by layer with a tailored scan track. The sintered alloy contained three types of defects comprising micron sized voids or cracks occurring at the cluster boundaries and larger cracks at the “weld line” boundaries. Unexpected good mechanical properties are achieved despite the observed microstructural defects and the laser sintered Co-Cr-Mo alloy seems very defect tolerant. This positive effect is ascribed to the strong structural hierarchies found in the laser sintered CoCrMo alloy. 

  • 8. Rättö, Peter
    et al.
    Joanna, Hornatowska
    Xiao, Changhong
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Osamu, Terasaki
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Cracking mechanisms of clay-based and GCC-based coatings2011In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 26, no 4, p. 485-492Article in journal (Refereed)
    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.

  • 9.
    Stevens, Sam M.
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Xiao, Changhong
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Klingstedt, Miia
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Grüner, Daniel
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Terasaki, Osamu
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    An Appraisal of High Resolution Scanning Electron Microscopy Applied To Porous Materials2009In: JEOL News, Vol. 44, no 1, p. 17-22Article in journal (Refereed)
    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.

  • 10. Ström, Göran
    et al.
    Hornatowska, Joanna
    Xiao, Changhong
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Terasaki, Osamu
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    A novel SEM cross-section analysis of paper coating for separation of latex from void volume2010In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 25, no 1, p. 107-113Article in journal (Refereed)
    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.

  • 11.
    Xiao, Changhong
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    A structural investigation into the complexity of mesoporous silica crystals: From a view of curvature and micellar interaction to quasicrystallinity2012Doctoral 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.

  • 12.
    Xiao, Changhong
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Fujita, Nobuhisa
    Miyasaka, Keiichi
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Sakamoto, Yasuhiro
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Terasaki, Osamu
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Dodecagonal tiling in mesoporous silica2012In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 487, no 7407, p. 349-353Article in journal (Refereed)
    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.

  • 13.
    Xiao, Changhong
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Keiichi, Miyasaka
    Osamu, Terasaki
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Structures of the C14GlutANa surfactant liquid crystalsManuscript (preprint) (Other academic)
1 - 13 of 13
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