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Bicontinuous Cubic Mesoporous Materials with Biphasic Structures
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
2011 (English)In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 17, no 48, 13510-13516 p.Article 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.

##### Place, publisher, year, edition, pages
2011. Vol. 17, no 48, 13510-13516 p.
##### Keyword [en]
bicontinuous structures, epitaxial growth, liquid crystals, mesoporous materials
##### National Category
Chemical Sciences
##### Research subject
Structural Chemistry
##### Identifiers
ISI: 000298059600019OAI: oai:DiVA.org:su-82372DiVA: diva2:567459
Available from: 2012-11-13 Created: 2012-11-13 Last updated: 2017-12-07Bibliographically approved
##### In thesis
1. A structural investigation into the complexity of mesoporous silica crystals: From a view of curvature and micellar interaction to quasicrystallinity
Open this publication in new window or tab >>A structural investigation into the complexity of mesoporous silica crystals: From a view of curvature and micellar interaction to quasicrystallinity
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. 110 p.
##### Keyword
electron microscopy, mesoporous silica, quasicrystal, minimal surface
##### National Category
Chemical Sciences
##### Research subject
Structural Chemistry
##### Identifiers
urn:nbn:se:su:diva-82382 (URN)978-91-7447-602-6 (ISBN)
##### 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

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