@phdthesis{Balzer2018,
  author    = {Balzer, Christian},
  title     = {Adsorption-Induced Deformation of Nanoporous Materials — in-situ Dilatometry and Modeling},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-157145},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2018},
  abstract  = {The goal of this work is to improve the understanding of adsorption-induced deformation in nanoporous (and in particular microporous) materials in order to explore its potential for material characterization and provide guidelines for related technical applications such as adsorption-driven actuation. For this purpose this work combines in-situ dilatometry measurements with in-depth modeling of the obtained adsorption-induced strains. A major advantage with respect to previous studies is the combination of the dilatometric setup and a commercial sorption instrument resulting in high quality adsorption and strain isotherms. The considered model materials are (activated and thermally annealed) carbon xerogels, a sintered silica aerogel, a sintered hierarchical structured porous silica and binderless zeolites of type LTA and FAU; this selection covers micro-, meso- and macroporous as well as ordered and disordered model materials. All sample materials were characterized by scanning electron microscopy, gas adsorption and sound velocity measurements. In-situ dilatometry measurements on mesoporous model materials were performed for the adsorption of N2 at 77 K, while microporous model materials were also investigated for CO2 adsorption at 273 K, Ar adsorption at 77 K and H2O adsorption at 298 K. Within this work the available in-situ dilatometry setup was revised to improve resolution and reproducibility of measurements of small strains at low relative pressures, which are of particular relevance for microporous materials. The obtained experimental adsorption and strain isotherms of the hierarchical structured porous silica and a micro-macroporous carbon xerogel were quantitatively analyzed based on the adsorption stress model; this approach, originally proposed by Ravikovitch and Neimark, was extended for anisotropic pore geometries within this work. While the adsorption in silica mesopores could be well described by the classical and analytical theory of Derjaguin, Broekhoff and de Boer, the adsorption in carbon micropores required for comprehensive nonlocal density functional theory calculations. To connect adsorption-induced stresses and strains, furthermore mechanical models for the respective model materials were derived. The resulting theoretical framework of adsorption, adsorption stress and mechanical model was applied to the experimental data yielding structural and mechanical information about the model materials investigated, i.e., pore size or pore size distribution, respectively, and mechanical moduli of the porous matrix and the nonporous solid skeleton. The derived structural and mechanical properties of the model materials were found to be consistent with independent measurements and/or literature values. Noteworthy, the proposed extension of the adsorption stress model proved to be crucial for the correct description of the experimental data. Furthermore, it could be shown that the adsorption-induced deformation of disordered mesoporous aero-/xerogel structures follows qualitatively the same mechanisms obtained for the ordered hierarchical structured porous silica. However, respective quantitative modeling proved to be challenging due to the ill-shaped pore geometry of aero-/xerogels; good agreement between model and experiment could only be achieved for the filled pore regime of the adsorption isotherm and the relative pressure range of monolayer formation. In the intermediate regime of multilayer formation a more complex model than the one proposed here is required to correctly describe stress related to the curved adsorbate-adsorptive interface. Notably, for micro-mesoporous carbon xerogels it could be shown that micro- and mesopore related strain mechanisms superimpose one another. The strain isotherms of the zeolites were only qualitatively evaluated. The result for the FAU type zeolite is in good agreement with other experiments reported in literature and the theoretical understanding derived from the adsorption stress model. On the contrary, the strain isotherm of the LTA type zeolite is rather exceptional as it shows monotonic expansion over the whole relative pressure range. Qualitatively this type of strain isotherm can also be explained by the adsorption stress model, but a respective quantitative analysis is beyond the scope of this work. In summary, the analysis of the model materials' adsorption-induced strains proved to be a suitable tool to obtain information on their structural and mechanical properties including the stiffness of the nonporous solid skeleton. Investigations on the carbon xerogels modified by activation and thermal annealing revealed that adsorption-induced deformation is particularly suited to analyze even small changes of carbon micropore structures.},
  subject      = {Nanopor{\"o}ser Stoff},
  language  = {en}
}
@phdthesis{Wagenhoefer2014,
  author    = {Wagenh{\"o}fer, Julian},
  title     = {Mikro- und mesopor{\"o}se Silicate als Wirkstoffspeichersysteme},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-103848},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2014},
  abstract  = {Mesopor{\"o}se Silica-Materialien (MSM) und mikropor{\"o}se Zeolithe besitzen große innere Oberfl{\"a}chen und eine damit verbundene hohe Speicherkapazit{\"a}t von verschiedenen Molek{\"u}len. Auf Grund dieser Eigenschaften stehen por{\"o}se, silicatische Materialien seit etwa 10 Jahren im Focus der Entwicklung neuartiger Wirkstoffspeichersysteme (WSS). Die innerhalb dieser Thematik ver{\"o}ffentlichten wissenschaftlichen Arbeiten konnten die Fragestellungen nach dem exakten Mechanismus der Wirkstoffspeicherung und Wiederfreisetzung bisher nicht komplett beantworten. Die vorliegende Arbeit besch{\"a}ftigt sich im Besonderen mit der Beladung und Abgabe des Lokalan{\"a}sthetikum Lidocain-Hydrochlorid (LidHCl) in bekannten MSM wie SBA15, MCM41 oder HMS, sowie in unterschiedlich modifizierten Zeolithen vom Typ FAU und BEA. Zus{\"a}tzlich wurde der Einfluss von organischen Ankergruppen innerhalb der Porenstruktur von SBA15 auf dessen Sorptions-eigenschaften hin untersucht. Ziel der Promotionsarbeit ist die Aufkl{\"a}rung des Speicher- und Freisetzungs-mechanismus dieses speziellen Speichersystems. Dazu wurden zun{\"a}chst detaillierte Analysen der reinen und der mit Wirkstoff beladenen Matrizes via N2-Sorption (BET-, BJH-, t-plot-Methode), XRD, SAXS, DSC und TG durchgef{\"u}hrt. Außerdem wurden grafische Profile erstellt, die das Verh{\"a}ltnis der ad- bzw. desorbierten Wirkstoffmengen gegen die bei der Beladung eingesetzten Wirkstoffkonzentrationen (Speicherprofil) bzw. gegen die bei der Wiederfreisetzung verstrichene Zeit (Freisetzungsprofil) wiedergeben. Durch die Kombination dieser Untersuchungsmethoden konnte der jeweilige Sorptionsmechanismus, sowie der Speicherort der Wirkstoffmolek{\"u}le innerhalb der ausgew{\"a}hlten Matrix erfasst werden. Der Vergleich der verschiedenen, hier untersuchten Speichersysteme zeigt, dass neben der Porengr{\"o}ße, die Art der Adsorbens-Adsorbat-Wechselwirkung, aber auch die Stabilit{\"a}t der Porenstruktur einen großen Einfluss auf die Sorption von Molek{\"u}len nimmt.},
  subject      = {Silicate},
  language  = {de}
}