Authors: Wieland, Florian D. C.
Title: Formation of organic and inorganic thin films at the aqueous solution-gas interface
Language (ISO): en
Abstract: Interfaces are of great importance as there processes can be observed which are governed by the properties of the neighboring media. The phenomena appearing at such phase boundaries can be significantly altered compared to the bulk. The investigation of interfacial reactions is crucial as the knowledge on the mechanisms can help to understand and control adsorption and growth processes. In this thesis the structure of different modified interfaces along with the influence on the adsorption of iron compounds is studied by different in-situ x-ray scattering techniques being x-ray reflectivity, grazing incidence diffraction and surface sensitive x-ray absorption spectroscopy. The structure of the solution-air interface modified by mono molecular films was investigated as function of the pH value in the interfacial region. The grade of the lateral linking of polysiloxane membranes was found to depend strongly on the pH condition of the subphase, thus offering the possibility to tune the structure and homogeneity. In natural systems complex materials and structures are formed by organisms holding fasci- nating properties which surpass materials manufactured by mankind. Understanding the growth principles can yield the development of new materials with outstanding properties. In nature the control is provided by different mechanisms one being the interaction with interfaces. In order gain insight to the early stages of the nucleation of iron compounds at cell membrane like structures, in situ x-ray experiments were performed to evaluate the structure on sub nanometer length scales. XRR and GID experiments proved the formation of structures at the solution air interface lacking long range order. X-ray absorption spectroscopy measurements revealed the existence of a short range order around the iron atoms. Depending on solution parameters the ongoing process bears the formation of crystalline structures. The stabilization of interfaces can be performed by surfactants or nanoparticles which is important for the production of emulsion and foams. The combined use of both educts promises advantages due to synergetic effects. By combining a solution containing nanoparticles and surfactants composite nanoparticles form. The adsorption of these composite nanoparticles was investigated by x-ray reflectivity measurements showing the formation of films composed of a single mono layer. Furthermore, the experiments proved that the degree of surface adsorption depends on the ratio between nanoparticles and surfactants.
Subject Headings: adsorption
iron complex
Langmuir layer
x-ray absorption spectroscopy
x-ray reflectivity
Subject Headings (RSWK): Adsorption
Grenzflächenaktiver Stoff
Issue Date: 2012-06-04
Appears in Collections:Experimentelle Physik I

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