Putz Florian, Morak Roland, Elsaesser Michael S, Balzer Christian, Braxmeier Stephan, Bernardi Johannes, Paris Oskar, Reichenauer Gudrun, Hüsing Nicola
Chemistry and Physics of Materials, Paris Lodron University Salzburg, 5020 Salzburg, Austria.
Institute of Physics, Montanuniversität Leoben, 8700 Leoben, Austria.
Chem Mater. 2017 Sep 26;29(18):7969-7975. doi: 10.1021/acs.chemmater.7b03032. Epub 2017 Aug 31.
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 sol-gel 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 material's macroporosity is also reflected in its mechanical properties; i.e., the Young's 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.
结构层次、孔隙率以及各向同性/各向异性是与多孔材料的机械性能及功能密切相关的因素。然而，尽管自然界中存在诸如骨骼或木材等各向异性且具有层次结构的多孔材料，但在实验室中制备其合成对应物却很困难。我们首次报道了一种将溶胶 - 凝胶工艺与剪切诱导取向相结合的直接方法，以制备在介孔和大孔水平上均表现出各向异性的分级二氧化硅整体材料。所得材料由支柱的各向异性大孔网络组成，这些支柱包含二维六方有序排列的圆柱形介孔。虽然介孔的各向异性是液晶模板形成的孔的固有特征，但大孔的各向异性是由网络的剪切诱导产生的。扫描电子显微镜和小角X射线散射表明，大多数形成网络的支柱都朝向剪切方向排列；对散射数据的定量分析证实，大约40%的支柱体积呈现出择优取向。材料大孔率的各向异性也反映在其机械性能上；即，在施加剪切力的方向与其垂直方向之间，杨氏模量相差近2倍。出乎意料的是，材料的吸附诱导应变几乎没有各向异性。
