Computational Methods to Evaluate Gas Adsorption and Small Angle Scattering Data from Hierarchically Porous Materials
Research output: Thesis › Doctoral Thesis
The objective of this thesis was the determination and description of adsorption induced deformation in different monolithic hierarchically nanoporous materials. These included two synthetic materials, monolithic hierarchically nanoporous silica and carbon, and one biological material in human root dentin. The mesoscopic structure of the silica material is highly similar to SBA-15, which was used to study adsorption induced deformation with in-situ adsorption small angle x-ray scattering (SAXS) in earlier works, and is equally suited as a model material to investigate adsorption and adsorption induced deformation. The silica monoliths are built up from a disordered network of struts, which are about 1 µm in length and 400 nm in diameter. Everey strut exhibits 2-D hexagonally ordered, cylindrical mesopores with a diameter of 6-7 nm and lattice constant of ~10 nm. Depending on the materials thermal history, different amount of accessible micropores with a characteristic size of <2 nm are embedded in the silica mesopore walls. The monolithic character enables to measure macroscopic deformation using in-situ adsorption dilatometry.In connection with in-situ small angle neutron scattering (SANS), the deformation induced by adsorption of water in three silica materials exhibting different amounts of micropores was determined. The small angle neutron scattering and dilatometry strain isotherms were succesfully modelled using a macroscopic, thermodynamic model of adsorption induced deformationfrom literature. So-called ‘apparent-deformations’, which occur in in-situ adsorption SAXS data of a monolithic, hierarchically porous materials, determined form the difference between water strain isotherms obtained with SAXS and SANS on the same silica material, were determined and successfully modelled using a simple, hierarchical pore model. During the investigation of apparent strains, subtle effects pertaining to the process of adsorption and the compressive or tensile nature of apparent strains were observed, hinting at a unique process of water adsorption in silica materials. In-situ n-pentane and water adsorption SANS and dilatometry experiments on monolithic, hierarchically nanoprorous carbon materials were conducted. These carbon materials exhibit the macroscopic strut-network structure of monolithic silica materials, but on the mesoscopic level they are exactly the inverse of the silica materials mesopore structure, where 2-D hexagonally ordered carbon nanowires with a diameter of about 6-7 nm and a lattice constant of ~10 nm. To interpret the strain isotherms acquired on tree different carbons with different amount of micropores, a model of adsorption in concave mesopore spaces was adapted. This model was able to qualitatively describe nitrogen and n-pentane adsorption isotherms. N-pentane strain isotherms of all carbon sample were interpreted and quantified using the results of the adsorption model. Finally, in-situ water-absorption SAXS data were measured on human root dentin. Using correlation length, swelling of collagen situated between crystalline mineral platelets was observed. Additionally, hints of filling of structures in human root dentin according to their hierarchical level of structures were found.
|Translated title of the contribution||Computergestützte Methoden zur Evaluierung von Gasadsorption und Kleinwinkelstreudaten hierarchisch poröser Materialien|
|Award date||30 Jun 2020|
|Publication status||E-pub ahead of print - 31 Jul 2020|