Evelin Jaehne

The Route to Functional Graphene Oxide

We report on an easy-to-use, successful, and reproducible route to synthesize functionalized graphite oxide (GO) and its conversion to graphene-like materials through chemical or thermal reduction of GO. Graphite oxide containing hydroxyl, epoxy, carbonyl, and carboxyl groups loses mainly hydroxyl and epoxy groups during reduction, whereas carboxyl species remain untouched. The interaction of functionalized graphene with fluorescent methylene blue (MB) is investigated and compared to graphite, fully oxidized GO, as well as thermally and chemically reduced GO. Optical absorption and emission spectra of the composites indicate a clear preference for MB interaction with the GO derivatives containing a large number of functional groups (GO and chemically reduced GO), whereas graphite and thermally reduced GO only incorporate a few MB molecules. These findings are consistent with thermogravimetric, X-ray photoelectron spectroscopic, and Raman data recorded at every stage of preparation. The optical data also indicate concentration-dependent aggregation of MB on the GO surface leading to stable MB dimers and trimers. The MB dimers are responsible for fluorescence quenching, which can be controlled by varying the pH value.

Self-assembling adhesion promoters for corrosion resistant metal polymer interfaces

The self-assembly process has been investigated for the replacement of the present chromating procedure on reactive metals like aluminium and to improve the lacquer adhesion and corrosion inhibition. It will be shown, that self-assembled layers can affect adhesion and corrosion inhibition on aluminium and its alloys. For self-assembly molecules (SAMs) substances are required which are able to react spontaneously on the surface for which terminated alkyl-phosphonic and phosphoric acid monoalkyl esters have been synthesised. The best anchor groups for aluminium were ascertained by pH-dependent flotation tests, dynamic contact angle measurements and corrosion tests. Grazing angle Fourier transform infrared spectroscopy (FTIR), angle dependent X-ray photoelectron spectroscopy (XPS) and Auger measurements show the existence and orientation of these new molecular structures. Model surface reactions with isocyanates demonstrate the binding capability to the lacquer.

Synthesis of adhesion promoters for grafting polythiophene onto metal oxides

A new class of compounds, ω-(thiophen-3-yl) alkyl phosphonic acids, was used to link conductive polythiophene layers and several metal oxide substrates. In general, the adhesion between polythiophene films and metal substrates is insufficient for technical and microelectronic applications. The use of adhesion promoters between the substrate and the polymer enables the formation of a strongly bonded composite. Adhesive compounds were synthesized which contained a phosphonic acid group attached to the substrate and a thienyl group for surface polymerization with thiophene monomers. The properties of these created adhesion promoters were characterized on several substrates by contact angle measurements and IR investigations. First successful attempts were made to obtain a structured polymer surface via micro-contact printing.

Ultrathin layers for adhesion promotion

Many technical applications require substances providing special abilities in connecting different materials to each other. Beginning from applications for corrosion inhibition to improved adhesion abilities of laquers on selected metals like aluminium, titanium or tantalum, some special adhesion promoters on base of phosponic acid and trichlorsilane were developed. At last electronic devices basing on conducting polymers need adhesion promoters to bound the conducting polymers to supporting materials consisting of technical polymers or silicon wafers and other inorganic surfaces. This requires new adhesion promoters with polymerizable groups like thiophen or pyrrol.

Reactive dispersions for corrosion inhibition

Several concepts have been developed for the improvement of adhesion promotion and corrosion inhibition of reactive metal surfaces, like aluminum. The aim of these studies was to replace the present technical procedure for pretreatment of aluminum surfaces with chromium acid. Therefore, the adsorption and organization process of mono- and bifunctional alkyl phosphonic acids and mono alkyl phosphoric acid esters has been investigated. The properties of the adsorbed SAMs were confirmed by industrial linked adhesion and corrosion tests. By functionalization of the terminal position with thiophene, molecules are prepared which can graft conducting polythiophene layers via surface polymerisation on silicon/metal substrates. Also polymeric nano-particles with phosphoric acid groups form thin and smooth well-packed films on aluminum surfaces. Stable core-shell polypyrrole (PPy) dispersions were prepared by using polystyrene (PST) or poly (styrene-co-butyl acrylate) (PST-co-BuA) as the core, and polypyrrole as the shell.

Surface modification of aluminium with reactive microgels

The adsorption and organisation process of reactive microgels has been investigated on technical aluminium. The aim was to replace the present chromating procedure on reactive metals like aluminium because this process was been considered as an ecological problem. By means of a two-step emulsion polymerization with phosphate substituted monomer we have obtained polymeric nano-particles with phosphate groups on the surface. The core is synthesized by copolymerization from styrene (St) and butyl acrylate (BuA). The results of several analytical methods like contact angle SEM or TEM measurements showed, that these microgels were able to adsorb spontaneously onto the substrate surface and subsequently a structured molecular order was formed. The properties of the adsorbed microgel layers were confirmed by industrial linked adhesion and corrosion tests.

Adhesion promoters for polythiophene

Polythiophene layers have been grafted onto silicon, iron, platinum and titanium for applications as organic semi-conducting films on solid surfaces. In general, the adhesion between the polymer films and substrates is insufficient for technical and microelectronic applications. The use of adhesion promoters between substrate and polymer and enables the formation of a strongly bonded composite. The polymers were synthesized by chemical or electrochemical surface polymerization.

Novel Modified Pyrrole Monomers, 2: Behaviour in Water Solutions

Aggregate formation of modified pyrroles was investigated in water and water/ethanol mixtures by means of light scattering for novel reactive single-chain alkyl phosphonate containing pyrrole units. The influence of concentration, pH, temperature and organic solvents on the evolution of the vesicle size is discussed. Long-chain alkyl phosphonates functionalized with pyrrole units form stable vesicles in water solutions. Lowering of the pH value results in a partial protonation of the phosphonate groups and in less electrostatic repulsion between the anionic groups, leading to larger vesicle diameters and higher tendency to aggregate. Addition of ethanol, as well as increase in temperature cause an increase in the aggregate size due to better solubility of alkyl phosphonates. The reactive vesicles are extremely interesting templates for oxidative polymerisation of pyrrole and they can provide the formation of novel particles based on conjugated polymers.