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Autor

  • Silbernagl, Dorothee (16)
  • Sturm, Heinz (10)
  • Ghasem Zadeh Khorasani, Media (6)
  • Cappella, Brunero (5)
  • Hodoroaba, Vasile-Dan (4)
  • Cano Murillo, Natalia (2)
  • Hahn, Marc Benjamin (2)
  • Agudo Jácome, Leonardo (1)
  • Altmann, Korinna (1)
  • Arnold, J. (1)
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Erscheinungsjahr

  • 2021 (1)
  • 2020 (2)
  • 2019 (3)
  • 2017 (1)
  • 2016 (3)
  • 2010 (1)
  • 2009 (2)
  • 2008 (1)
  • 2007 (2)

Dokumenttyp

  • Zeitschriftenartikel (13)
  • Beitrag zu einem Tagungsband (2)
  • Posterpräsentation (1)

Sprache

  • Englisch (15)
  • Deutsch (1)

Referierte Publikation

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  • nein (4)

Schlagworte

  • AFM (4)
  • Epoxy (4)
  • Mechanical properties (4)
  • Atomic force microscopy (3)
  • Boehmite (2)
  • Force-distance curves (2)
  • Indentation (2)
  • Interphase (2)
  • Rheology (2)
  • AFM cantilever vibration (1)
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Organisationseinheit der BAM

  • 6 Materialchemie (10)
  • 6.6 Physik und chemische Analytik der Polymere (10)
  • 6.1 Oberflächenanalytik und Grenzflächenchemie (4)
  • 1 Analytische Chemie; Referenzmaterialien (2)
  • 5 Werkstofftechnik (2)
  • 1.2 Biophotonik (1)
  • 1.4 Prozessanalytik (1)
  • 4 Material und Umwelt (1)
  • 4.0 Abteilungsleitung und andere (1)
  • 5.1 Materialographie, Fraktographie und Alterung technischer Werkstoffe (1)
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Reconstruction of a hidden topography by single AFM force-distance curves (2009)
Silbernagl, Dorothee ; Cappella, Brunero
Force–distance curves have been acquired with an Atomic Force Microscope on polymethyl methacrylate with embedded glass spheres. The glass spheres provide a stiff substrate with an irregular and complex topography hidden underneath a compliant and even polymer film. This situation is a special case of a mechanical double-layer, which we examined in detail in previous experiments. Up to now uniform and non-uniform polymer films on an even substrate were examined. The film thickness on each point of the sample surface was known and force–distance curves could be averaged in groups according to the film thickness. In this way we were able to develop a semi empirical approach which allows describing the shape of averaged force–distance curves depending on the Young’s moduli of the involved materials and on the film thickness. In this experiment we reconstruct a hidden topography, i.e., we determine the polymer thickness on each point of the sample by analyzing single force–distance curves with our semi empirical equation. The accuracy reached by this approach permits to obtain a reconstruction of the shape and position of the embedded particles limited by a maximum detection depth. Single curves are also analyzed qualitatively in order to locate areas where the adhesion at the polymer/glass interface is weak or the two phases are detached.
Mechanical properties of thin polymer films on stiff substrates (2010)
Silbernagl, Dorothee ; Cappella, Brunero
Force–displacement curves have been acquired with a commercial atomic force microscope on thin films of poly(n-butyl methacrylate) on glass substrates in order to examine the so-called 'mechanical double layer' topic, i.e. the influence of the substrate on the mechanical properties of the film in dependence of the film thickness. The hyperbolic fit, a novel semi-empirical equation introduced in previous articles, has been further corroborated. The interpretation of this equation has been deepened, yielding a quantitative and demonstrative characterization of the mechanical properties of double layers. Provided that the Young's moduli of bulk polymer and substrate are measured from the deformation curves, this mathematical model permits to fit the deformation–force curves on the double layers and to determine the thickness of the polymer films in wide range (0–200 nm).
Nanomechanical properties of mechanical double-layers: a novel semiempirical analysis (2007)
Silbernagl, Dorothee
Nanomechanical properties of polymer thin films measured by force-distance curves (2008)
Cappella, Brunero ; Silbernagl, Dorothee
Force–displacement curves have been acquired with a commercial atomic force microscope on thin films of poly(n-butyl methacrylate) on glass substrates. Different film thicknesses, from 10 up to 430 nm, were chosen to examine in detail the so called “mechanical double-layer” topic, i.e., the influence of the substrate on the determination of the mechanical properties of thin films. Taking advantage of the Hertz theory we calculated for all films the contact radius between tip and sample as a function of the applied load. Further Young's modulus of the samples was derived from the experimental data as a function of the applied load and, alternatively, of the deformation. The results of this analysis for 10 different film thicknesses were fitted with several half empirical equations proposed by several researchers. The focus of this work is to evaluate such existing half empirical theories for mechanical double-layers and to show the need for an alternative consistent approach.
Nanomechanica lProperties of Mechanical Double-Layers: A Novel Semiempirical Analysis (2007)
Cappella, Brunero ; Silbernagl, Dorothee
Force-displacement curves have been acquired with a commercial atomic force microscope on a thin film of poly(n-butyl methacrylate) on glass substrates. The film thickness is nonuniform, ranging in the measured area from 0 to 30 nm, and gives the possibility to survey the so-called "mechanical double-layer" topic, i.e., the influence of the substrate on the mechanical properties of the film in dependence of the film thickness. The stiffness and the deformation for each force-distance curve were determined and related to the film thickness. We were able to estimate the resolution of the film thickness that can be achieved by means of force-distance curves. By exploiting the data acquired in the present and in a previous experiment, a novel semiempirical approach to describe the mechanical properties of a mechanical double-layer is introduced. The mathematical model, with which deformation-force curves can be described, permits to calculate the Young's moduli of film and substrate in agreement with literature values and to determine the film thickness in agreement with the topography.
Mechanical properties of Boehmite evaluated by Atomic Force Microscopy experiments and Molecular Dynamic Finite Element simulations (2016)
Fankhänel, J. ; Silbernagl, Dorothee ; Ghasem Zadeh Khorasani, Media ; Daum, B. ; Kempe, A. ; Sturm, Heinz ; Rolfes, R.
Boehmite nanoparticles show great potential in improving mechanical properties of fiber reinforced polymers. In order to predict the properties of nanocomposites, knowledge about the material parameters of the constituent phases, including the boehmite particles, is crucial. In this study, the mechanical behavior of boehmite is investigated using Atomic Force Microscopy (AFM) experiments and Molecular Dynamic Finite Element Method (MDFEM) simulations. Young’s modulus of the perfect crystalline boehmite nanoparticles is derived from numerical AFM simulations. Results of AFM experiments on boehmite nanoparticles deviate significantly. Possible causes are identified by experiments on complementary types of boehmite, that is, geological and hydrothermally synthesized samples, and further simulations of imperfect crystals and combined boehmite/epoxy models. Under certain circumstances, the mechanical behavior of boehmite was found to be dominated by inelastic effects that are discussed in detail in the present work.The studies are substantiated with accompanying X-ray diffraction and Raman experiments.
Influence of film-substrate adhesion on the mechanical properties of thin polymer films (2009)
Silbernagl, Dorothee ; Sturm, Heinz ; Cappella, Brunero
Influences of nano effects on the flow phenomena of self-compacting concrete (2016)
Schmidt, Wolfram ; Weba, Luciana ; Silbernagl, Dorothee ; Mota Gassó, Berta ; Höhne, Patrick ; Sturm, Heinz ; Pauli, Jutta ; Resch-Genger, Ute ; Steinborn, Gabriele
Chemical admixtures like superplasticisers or stabilising agents are of ever increasing importance for modern concrete technology. They liberate the workability of concrete from its dependency on water content, and thus, open the gate towards innovative and future oriented concrete technologies such as selfcompacting concrete. Meanwhile admixtures have become common practice in concrete technology, but the understanding of these highly complex polymers in the entire concrete system lags far behind their application. Due to its complex time-dependent, multi-phase and multi-scale behaviour, flowable concrete systems are highly complicated and cannot be described comprehensively by simple models. It is therefore extremely challenging to identify the relevant parameters that predominantly control flow phenomena on different size scales, since these may occur on any scale between the nano scale (e.g. superplasticizer adsorption) and macro scale (e.g. grading of the aggregates). The present study discusses fundamental mechanisms at the interface between particle or hydrate surfaces and the fluid phase at a very early stage of concrete formation, and links these effects to macroscopic flow phenomena. Methods are discussed that appear promising interdisciplinary tools for enhancement of the understanding of the relevant interactions that are responsible for the macroscopic flow of flowable concrete.
A Mechanistic Perspective on Plastically Flexible Coordination Polymers (2020)
Bhattacharya, Biswajit ; Michalchuk, Adam ; Silbernagl, Dorothee ; Rautenberg, Max ; Schmid, Thomas ; Feiler, Torvid ; Reimann, K. ; Ghalgaoui, A. ; Sturm, Heinz ; Paulus, B. ; Emmerling, Franziska
Mechanical flexibility in single crystals of covalently bound materials is a fascinating and poorly understood phenomenon. We present here the first example of a plastically flexible one-dimensional (1D) coordination polymer. The compound [Zn(m-Cl)2(3,5-dichloropyridine)2]n is flexible over two crystallographic faces. Remarkably, the single crystal remains intact when bent to 1808. A combination of microscopy, diffraction, and spectroscopic studies have been used to probe the structural response of the crystal lattice to mechanical bending. Deformation of the covalent polymer chains does not appear to be responsible for the observed macroscopic bending. Instead, our results suggest that mechanical bending occurs by displacement of the coordination polymer chains. Based on experimental and theoretical evidence, we propose a new model for mechanical flexibility in 1D coordination polymers. Moreover, our calculations propose a cause of the different mechanical properties of this compound and a structurally similar elastic material
Short- and long-range mechanical and chemical interphases caused by interaction of Boehmite (γ-AlOOH) with anhydride-cured epoxy resins (2019)
Ghasem Zadeh Khorasani, Media ; Elert, Anna-Maria ; Hodoroaba, Vasile-Dan ; Agudo Jácome, Leonardo ; Altmann, Korinna ; Silbernagl, Dorothee ; Sturm, Heinz
Understanding the interaction between boehmite and epoxy and the formation of their interphases with different mechanical and chemical structures is crucial to predict and optimize the properties of epoxy-boehmite nanocomposites. Probing the interfacial properties with atomic force microscopy (AFM)-based methods, especially particle-matrix long-range interactions, is challenging. This is due to size limitations of various analytical methods in resolving nanoparticles and their interphases, the overlap of interphases, and the effect of buried particles that prevent the accurate interphase property measurement. Here, we develop a layered model system in which the epoxy is cured in contact with a thin layer of hydrothermally synthesized boehmite. Different microscopy methods are employed to evaluate the interfacial properties. With intermodulation atomic force microscopy (ImAFM) and amplitude dependence force spectroscopy (ADFS), which contain information about stiffness, electrostatic, and van der Waals forces, a soft interphase was detected between the epoxy and boehmite. Surface potential maps obtained by scanning Kelvin probe microscopy (SKPM) revealed another interphase about one order of magnitude larger than the mechanical interphase. The AFM-infrared spectroscopy (AFM-IR) technique reveals that the soft interphase consists of unreacted curing agent. The long-range electrical interphase is attributed to the chemical alteration of the bulk epoxy and the formation of new absorption bands.
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