Publikationen

The siloxyalanes [(Et3SiOAlH2)2AlH3]n (1), [tBuMe2SiOAlH2]2 (2), [(tBuMe2SiO)2AlH]2 (3), and [(tBuMe2SiO)5Al2H] (4) have been synthesized and characterized by IR and NMR spectroscopic means. By X-ray diffraction studies on single crystals it was established that molecule 1 is a coordination polymer in the solid state with tetrameric units [Et3SiOAlH2]4 (almost linear Al∙∙∙Al∙∙∙Al∙∙∙Al arrangement) interlinked by Al2H6 groups to form a one-dimensional chain (formal description with neutral building blocks). Compound 3 is dimeric through Al-O contacts with a cis orientation of the hydride ligands with respect to the central Al2O2 cycle. Compound 4 may be described as a double adduct between the two Lewis acid-base compounds (tBuMe2SiO)2AlH and Al(OSiMe2tBu)3. The bulkiness of the substituents on the silicon atoms plays an important role in the aggregation of the compounds. Hydride bridging between molecules or within the molecular entities is only observed in compound 1.

Thermally and chemically durable hydrophobic oleophobic coatings, containing different ceramic particles such as SiO2, SiC, Al2O3, which can be alternative instead of Teflon, have been developed and applied on the aluminum substrates by spin-coating method. Polyimides, which are high-thermal resistant heteroaromatic polymers, were synthesized, and fluor oligomers were added to these polymers to obtain hydrophobic-oleophobic properties. After coating, Al surface was subjected to Taber-abrasion, adhesion, corrosion, and thermal tests. The effects of the particle size of ceramic powders, organic matrix, and heat on the coating material were investigated. Coating material was characterized by FTIR spectrophotometer. Surface properties and thermal resistance of the coating materials were investigated by SEM and TGA analyses. After thermal curing, contact angles of these coatings with H2O and n-hexadecane were measured. It was observed that coatings like ceramic particles are more resistant against scratch and abrasion than the other coatings. Also, they are harder than coatings, which do not include ceramic particles. It was seen that coatings, containing Fluorolink D10H, have high-contact angles with water and n-hexadecane.

The optical and electrical properties of two types of wet chemical processed tin doped indium oxide (ITO) films deposited by spin coating technique as well as of a commercial sputtered ITO film have been measured. The transmission and reflection spectra in the wavelength range 0.25 to 20 µm have been simulated using the Scout 2 software with different dielectric function models. The electrical parameters obtained from the modeling are compared with those obtained experimentally. The optical data of a low porosity (28%), low specific resistivity (ρ = 6.3 x 10-4 Ω cm) sol-gel film deposited from an ethylene glycol solution of In and Sri salts and sintered at 550 °C, as well as those of all Asahi Glass sputtered film (ρ = 1.9 x 10-4 Ω cm) have been successfully fitted with the Drude model and the electrical parameters deduced from the fitting are in good agreement with the measured ones. On the other hand, the best fit of the optical data of a thick single coating prepared using dispersed crystalline nanoparticles was obtained using the Bruggemann effective medium theory coupled with the extended Drude model. The electrical and structural parameters deduced from the fitting are also in good agreement with those measured. The results are discussed in terms of the morphology of the coatings.

Structure zone models (Movchan-Demchishin, Thornton, etc.) have been proposed to predict the morphology of metal and metal-oxide films produced by PVD or CVD processes. An original model was proposed for metal-oxide coatings made by the sol-gel process, based on a thorough experimental study of the microstructure of many coatings either obtained at INM or reported by other laboratories. The different morphologies – granular, layered, columnar – were described in terms of a parameter q = ICS/SLT, where ICS is a so-called "intrinsic crystallite size" and SLT is the single layer thickness and the homologous temperature T-H = T-Sintering/T-Melting. The influence of these morphologies and parameters on the electrical properties of transparent conducting ZnO:Al coatings is reported.

Transparent coating systems applicable on plastics surfaces by a spray technique are presented. The coatings are based on highly photocatalytically active nanoscaled titania powders, surface modified with silanes containing organic or fluoro-organic side chains. The modification allows for the introduction of the particles in organic inorganic hybrid NANOMER (c) coating systems. In the wet film-due to the evaporation of the solvents – a decompatibilisation of the coated particles to the matrix results in a self-organising gradient layer formation with an up-concentration of the active particles at the interface layer between coating and air. After activation by irradiation with artificial or natural UV-light, highly active transparent photocatalytic coatings for a great variety of materials are obtained. (c) 2005 Elsevier B.V. All rights reserved.

A high-throughput method for viscosity measurement was developed and tested for nanocomposite sols with an easy-to-clean (ETC) effect. The method is based on doping of sols with viscosity sensitive fluorescent dye 4,4'-bis-(2-benzoxazolyl)-stilbene (BOS) and acquisition of fluorescence intensity data. The spectroscopic data were correlated with viscosity data derived from mechanical measurements with a rotational viscometer and show an exponential correlation of both mechanical and spectroscopic measurement methods in the relevant data space of 3-5 mPa center dot s. For application of the spectroscopic viscosity measurement as a high-throughput assay doping of sols with BOS slurry was carried out with an automated liquid handling system, and spectroscopic measurements were performed with a fluorescence microplate reader.

A high-throughput screening method for the exploration of optimal curing parameters and resistance to solvents of NANOMER (R) coating materials based on the temperature-dependent swellability was developed. The screening method was first tested using a model sol made of pre-hydrolyzed (3-glycidoxypropyl)triethoxysilane (GPTES), tetraethoxysilane (TEOS), (heptadecafluoro-1,1,2,2-tetrahydrodecyl)triethoxysilane (FTS) and zirconium complex (prepared of zirconium-tert-butoxide complexed with acetylacetonate) charged with reactive diluent trimethylolpropan-triglycidether and defined amounts of fluorescein and cured at different temperatures. Afterwards, fluorescein was extracted with sodium hydroxide solution and the optical density of the supernatant of all samples was measured at 490 nm which is sensitive to the dye concentration. The optical density (OD) correlates with the degree of curing. According to this screening a temperature >= 140°C is necessary for proper curing. The time dependence of extraction reveals information on resistance against sodium hydroxide solution, i. e. alkali resistance. The time dependent extraction of fluorescein at 60°C of coatings cured at 100 and 140°C, respectively, shows a better resistance against 0.1 M sodium hydroxide solution for the one cured at 140°C, especially in the time range 10 – 60 min. The whole process – sol preparation, mixing of sols with dye, extraction, and optical spectroscopy-can be performed automatically. Further testes were made to proof the usability of this process. 96 hybrid materials were screened in regard to their alkali resistance and finally, a total number of 14 clear organic-inorganic hybrid coating systems with improved stability against sodium hydroxide solution were derived from this study.

Transparent nanocrystalline pure anatase titania (nano-TiO2) was synthesized by hydrothermal process at 200°C. Photocatalytic activity of the nano-TiO2 as in the form of sol was tested for degradation of Methylene Blue (MB) and Reactive Red 120 (RR-120) in aqueous solutions. Structural and physico-chemical properties of the nano-TiO2 were characterized using powder XRD, SEM, BET, FTIR and elemental analyses. Complete photodegradation of RR-120 was successfully achieved by aid of the nano-TiO2 whereas NIB was not degraded, maybe because of reversible color change in nano-TiO2 sol/MB mixture after the LTV irradiation was stopped. Potocatalytic activity of the synthesized the nano-TiO2 for degradation of RR-120 was compared with Degussa P-25 at optimum conditions determined for RR-120. It was found that the nano-TiO2 can be repeatedly used with higher photocatalytic activity than Degussa P-25.