In Situ Small-Angle Neutron Scattering Investigation of Adsorption-Induced Deformation in Silica with Hierarchical Porosity
In Situ Small-Angle Neutron Scattering Investigation of Adsorption-Induced Deformation in Silica with Hierarchical Porosity
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DOI：
10.1021/acs.langmuir.9b01375
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发表时间：
2019-08
期刊：
影响因子：
3.9
通讯作者：
Lukas Ludescher;Roland Morak;C. Balzer;Anna M. Waag;S. Braxmeier;Florian Putz;S. Busch;G. Gor;A. Neimark;N. Hüsing;G. Reichenauer;O. Paris
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作者：
Lukas Ludescher;Roland Morak;C. Balzer;Anna M. Waag;S. Braxmeier;Florian Putz;S. Busch;G. Gor;A. Neimark;N. Hüsing;G. Reichenauer;O. Paris
采用原位小角中子散射（SANS）和原位膨胀法研究了一系列具有分层孔隙度的二氧化硅样品的吸附诱导变形。单片样品由六边形有序圆柱形介孔和介孔壁内无序微孔的二维晶格构成的无序大孔支撑网络组成。通过分析SANS数据中有序介孔晶格的Bragg反射位移，得到了在介孔水平的应变等温线。因此，SANS本质上测量的是圆柱形介孔的径向应变，包括微孔变形引起的介孔壁体积变化。采用净相干中子散射长度密度为零的H2O/D2O吸附材料，以避免孔隙填充过程中强度变化带来的明显应变效应。与SANS相反，原位膨胀法获得的应变等温线是轴向和径向介孔变形以及微孔变形的结合结果。结合氮吸附等温线和水吸附等温线的信息，利用微/中孔变形理论模型定量分析应变数据，估计水-硅相互作用。结果表明，原位SANS为膨胀法提供了补充信息，并允许定量估计介孔壁的弹性特性。
Adsorption-induced deformation of a series of silica samples with hierarchical porosity has been studied by in situ small-angle neutron scattering (SANS) and in situ dilatometry. Monolithic samples consisted of a disordered macroporous network of struts formed by a 2D lattice of hexagonally ordered cylindrical mesopores and disordered micropores within the mesopore walls. Strain isotherms were obtained at the mesopore level by analyzing the shift of the Bragg reflections from the ordered mesopore lattice in SANS data. Thus, SANS essentially measured the radial strain of the cylindrical mesopores including the volume changes of the mesopore walls due to micropore deformation. A H2O/D2O adsorbate with net zero coherent neutron scattering length density was employed in order to avoid apparent strain effects due to intensity changes during pore filling. In contrast to SANS, the strain isotherms obtained from in situ dilatometry result from a combination of axial and radial mesopore deformation together with micropore deformation. Strain data were quantitatively analyzed with a theoretical model for micro-/mesopore deformation by combining information from nitrogen and water adsorption isotherms to estimate the water–silica interaction. It was shown that in situ SANS provides complementary information to dilatometry and allows for a quantitative estimate of the elastic properties of the mesopore walls from water adsorption.