The impact of synthesis parameters and structural properties, respectively, on mechanical properties of porous materials on different structural levels provides valuable information for designing materials for specific applications. Within this study, we apply two nonstandard approaches for determining the mechanical properties of the mesoporous backbone phase in a series of disordered SiO₂-based monolithic materials possessing hierarchical meso-macroporosity, that is, deformation upon mercury porosimetry and in situ dilatometry during nitrogen adsorption analysis. By using ordered porous model materials, the latter method has been recently proven to provide reliable mechanical moduli. This concept was now applied to a SiO₂ monolith developed for high-performance liquid chromatography exhibiting disordered hierarchical meso- and macroporosity, as well as a series of analogue phenyl-modified meso-macroporous SiO₂ monoliths with up to 36.1 at% organic modification. The phenyl group was introduced by adding phenyltrimethoxysilane to the sol–gel mixture. The study aimed at investigating in detail the impact of the organic modification on the morphology of the porous solid and the resulting mechanical properties. The study shows that both Hg porosimetry and in situ dilatometry performed during N₂ adsorption at 77 K provide similar and reasonable moduli of compression for the mesoporous backbone of the silica materials investigated. These data were compared with moduli of the macroscopic sample as determined from sound velocity measurements by describing the fully connected macroporous backbone with a foam model. The comparison reveals an otherwise overseen side effect of the organic modification of the silica framework: in contrast to the pure reference SiO₂ meso-macroporous monoliths, the hybrid material is composed of a more particulate morphology on the mesoscale, that is, mesoporous particles and corresponding necks between them are formed, which results in significant softening of the porous solid on the macroscale.

中文翻译：

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确定不同结构水平上具有分级孔隙率的无序材料的机械模量

合成参数和结构性能分别对不同结构水平的多孔材料机械性能的影响为设计特定应用的材料提供了有价值的信息。在这项研究中，我们应用了两种非标准方法来确定一系列无序 SiO ₂基整体材料中的中孔骨架相的机械性能，这些材料具有分级介孔大孔，即汞孔隙率法和氮吸附过程中的原位膨胀法变形分析。通过使用有序多孔模型材料，后一种方法最近已被证明可以提供可靠的机械模量。这个概念现在被应用于 SiO ₂为高效液相色谱开发的具有无序分级中孔和大孔孔隙率的整体材料，以及一系列具有高达 36.1 at% 有机改性的类似苯基改性的中孔大孔 SiO _{2整体材料。}通过向溶胶-凝胶混合物中添加苯基三甲氧基硅烷来引入苯基。该研究旨在详细研究有机改性对多孔固体形态和由此产生的机械性能的影响。研究表明，Hg 孔隙率测定法和原位膨胀测定法在 N ₂在 77 K 下的吸附为所研究的二氧化硅材料的中孔骨架提供了相似且合理的压缩模量。通过用泡沫模型描述完全连接的大孔骨架，将这些数据与由声速测量确定的宏观样品的模量进行比较。比较揭示了二氧化硅骨架的有机改性的另一个被忽视的副作用：与纯参考 SiO ₂中孔-大孔整体材料相比，混合材料由中尺度上更颗粒的形态组成，即中孔颗粒和它们之间形成相应的颈部，这导致宏观上多孔固体的显着软化。