Bioinspirierte Partikeladsorption: Polyelektrolyt-Multilayer auf strukturierten Substraten

Pollen sind in der Lage auf ihren Oberflächen Feinstaub zu fixieren. Diesem natürlichen Vorbild folgend war das Ziel dieser Arbeit die Entwicklung verschiedener Polyelektrolyt-Multilayer (PEM) auf glatten und strukturierten Substraten zur Erforschung der Korrelation von Oberflächeneigenschaften und...

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Bibliographic Details
Main Author: Große, Xenia
Contributors: Hampp, Norbert (Prof.) (Thesis advisor)
Format: Doctoral Thesis
Published: Philipps-Universität Marburg 2013
Online Access:PDF Full Text
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Pollen accumulates small particles like fine dust on their surface. Following this principle, different polyelectrolyte multilayers on flat and linearly structured silicon wafers were analysed in this thesis for the correlation of surface structure and the potential to immobilize particles. The strategic approach focuses on both topological and chemical aspects of the obtained surfaces. Novel and established multilayers (16 layers) were assembled on the flat and structured silicon surfaces by the layer-by-layer approach by dipping in oppositely-charged polyelectrolytes and were subsequently characterised. Utilised polyelectrolyte combinations of poly(L-lysine)/poly(L-glutamic acid), poly(allylamine)/ poly(L-glutamic acid) and poly(L-histidine)/poly(L-glutamic acid) were chosen upon the occurrence of similar surface functionality as pollen. The design of structures in the silicon substrates was inspired by pollen as well. A core problem in this project was the essential analysis of nm-sized coatings upon µm-sized substrates. A combination of energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, infrared spectroscopy, ellipsometry, X-ray reflectometry, atomic force microscopy, electron microscopy, as well as contact angle, streaming current and streaming potential measurements was applied to resolve these fundamental aspects. The structured substrates did not affect the coatings with respect to homogeneity and morphological reproduciblity in any observable way in all experiments. No difference in topology, roughness or the multilayer thickness occurred in comparison to multilayers on flat coatings and the structural transitions did not cause accumulations or holes in the coatings. Remarkably, topological differences were observed for the multilayer compositions: (PLL/PGA)8 provides 20 nm protrusions from a closed bottom layer, (PAH/PGA)8 results in a netlike surface structure with elevations up to 60 nm, whilst (PLH/PGA)8 shows globular shapes of 5 nm, partly in agglomerated form embedded in a conformal bottom laye. The latter provides a not yet reported surface topology. The occurrence of these tightly bound round structures can in all cases be explained by the random coil structure of the applied components. Effects of impurities and/or saturation effects could be ruled out during analyses. The resulting layer thickness obtained by physical and optical methods was found to be comparably thin with 37 nm ±2 nm for (PLL/PGA)8, 75 nm ±14 nm for (PAH/PGA)8 and 17 nm ±1 nm for (PLL/PGA)8. Coatings were highly reproducible, homogeneous and the thickness correlated with the growth type. Exponential, stronger exponential and linear behaviour was observed respectively upon analysis in solution and in dry state. Nevertheless, no real layer boundaries could be defined by optical, chemical or physical means. Based on preliminary stability-in-air and adhesion tests all coatings show sufficient stability and adhesiveness for spherical carbon for the potential application in customised filters. Mixed coatings seem to provide preferable properties here. In conclusion, the industrially accessible, cheap polyelectrolyte multilayers seem to provide an excellent coating for structured substrates as a basis for customised filters. Future investigations will be performed on a library of substrate structures to access their influence on adhesion.