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Formation Mechanism of Anionic Surfactant-Templated Mesoporous Silica
Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry. (Osamu Terasaki)
2006 (English)In: Chemistry of Materials, ISSN 0897-4756, Vol. 18, 3904-3914 p.Article in journal (Refereed) Published
Abstract [en]

The synthesis mechanism of anionic surfactant-templated mesoporous silica (AMS) is described. A family of highly ordered mesoporous silica structures have been synthesized via an approach based on the self-assembly of anionic surfactants and inorganic precursors by using aminopropylsiloxane or quaternized aminopropylsiloxane as the co-structure-directing agent (CSDA), which is a different route from previous pathways. Mesophases with differing surface curvatures, varying from cage type (tetragonal P42/mnm; cubic Pm-3n with modulations; cubic Fd-3m) to cylindrical (two-dimensional hexagonal p6mm), bicontinuous (cubic Ia-3d and Pn-3m), and lamellar have been obtained by controlling the charge density of the micelle surfaces by varying the degree of ionization of the carboxylate surfactants. Changing the degree of ionization of the surfactant results in changes of the surfactant packing parameter g, which leads to different mesostructures. Furthermore, variation of the charge density of positively charged amino groups of the CSDA also gives rise to different values of g. Mesoporous silicas, functionalized with amino and quaternary ammonium groups and with the various structures given above, have been obtained by extraction of the surfactant. This report leads to a deeper understanding of the interactions between the surfactant anions and the CSDA and provides a feasible and facile approach to the mesophase design of AMS materials.

Place, publisher, year, edition, pages
ACS , 2006. Vol. 18, 3904-3914 p.
Keyword [en]
mesoporous silica, anionic surfactant, formation mechanism
Research subject
Materials Science
URN: urn:nbn:se:su:diva-29613DOI: 10.1021/cm061107+OAI: diva2:234469
Available from: 2009-09-09 Created: 2009-09-08 Last updated: 2009-09-09Bibliographically approved
In thesis
1. Formation mechanism of anionic-surfactant-templated mesoporous silica (AMS)
Open this publication in new window or tab >>Formation mechanism of anionic-surfactant-templated mesoporous silica (AMS)
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This dissertation is focused on synthesis, characterization and formation mechanism of anionic-surfactant-templated mesoporous silica (AMS).

Structural control mechanisms of AMS are investigated. First, different ionization degree of anionic surfactant affected by the acidity or alkalinity of the synthesis system gives rise to different charging density of micelles and therefore determines the organic/inorganic interface curvature, producing mesophases from cage-type to cylindrical, bicontinuous and lamellar. Second, mesocage/mesocage electrostatic repulsive interaction affects the formation of cage-type mesostructure, which is derived from a full-scaled synthesis-field diagram of AMS. The mesocage/mesocage interaction changes with charge density of mesocages and gives rise to their different packing manners. Third, the structural properties of AMS materials could be tuned by molecular features of surfactant and co-structure-directing agent (CSDA).

The pore size of AMS is found to be controlled by alkyl chain length, ionization degree of surfactant and the CSDA/surfactant ratio. Alkyl chain length of surfactant determines size of micelles and thus mesopores. Larger ionization degrees of anionic surfactant give rise to smaller pore sizes due to thermodynamic coiling of alkyl chains of surfactant. The hydrophobic interactions between the pendant organic groups of CSDA on the silica wall and the hydrophobic core of the micelles drive a contraction of the mesopores.

A mesoporous silica with novel bicontinuous cubic Pn-3m structure has been prepared using a diprotic anionic surfactant. 3d-reconstruction of the structure shows that it is bicontinuous composed of an enantiomeric pair of 3d mesoporous networks that are interwoven with each other, divided by a D surface. Inverse replication suggests the possible presence of ordered complimentary micropores in the material.

Place, publisher, year, edition, pages
Stockholm: Department of Physical, Inorganic and Structural Chemistry, Stockholm University, 2009. 75 p.
mesoporous silica, anionic surfactant, formation mechanism, structural control
National Category
Other Basic Medicine
Research subject
Structural Chemistry
urn:nbn:se:su:diva-29628 (URN)978-91-7155-932-6 (ISBN)
Public defence
2009-10-06, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius vägen 16 B, Stockholm, 13:30 (English)
Available from: 2009-09-15 Created: 2009-09-08 Last updated: 2009-09-15Bibliographically approved

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