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Setting Directions : Anisotropy in Hierarchically Organized Porous Silica
VerfasserPutz, Florian ; Morak, Roland ; Elsaesser, Michael S. ; Balzer, Christian ; Braxmeier, Stephan ; Bernardi, Johannes ; Paris, Oskar ; Reichenauer, Gudrun ; Hüsing, Nicola
Erschienen in
Chemistry of Materials, Washington, 2017, Jg. 29, H. 18, S. 7969-7975
ErschienenWashington : American Chemical Society, 2017
DokumenttypAufsatz in einer Zeitschrift
Projekt-/ReportnummerI 1605-N20
URNurn:nbn:at:at-ubs:3-11822 Persistent Identifier (URN)
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Setting Directions [6.05 mb]
Zusammenfassung (Englisch)

Structural hierarchy, porosity, and isotropy/anisotropy are highly relevant factors for mechanical properties and thereby the functionality of porous materials. However, even though anisotropic and hierarchically organized, porous materials are well known in nature, such as bone or wood, producing the synthetic counterparts in the laboratory is difficult. We report for the first time a straightforward combination of solgel processing and shear-induced alignment to create hierarchical silica monoliths exhibiting anisotropy on the levels of both, meso- and macropores. The resulting material consists of an anisotropic macroporous network of struts comprising 2D hexagonally organized cylindrical mesopores. While the anisotropy of the mesopores is an inherent feature of the pores formed by liquid crystal templating, the anisotropy of the macropores is induced by shearing of the network. Scanning electron microscopy and small-angle X-ray scattering show that the majority of network forming struts is oriented towards the shearing direction; a quantitative analysis of scattering data confirms that roughly 40% of the strut volume exhibits a preferred orientation. The anisotropy of the materials macroporosity is also reflected in its mechanical properties; i.e., the Youngs modulus differs by nearly a factor of 2 between the directions of shear application and perpendicular to it. Unexpectedly, the adsorption-induced strain of the material exhibits little to no anisotropy.

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