Publikationen

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.

Polyimide-silica hybrid materials have been prepared through the sol-gel process by mixing various proportions of tetraethoxysilane (TEOS) with polyamic acids (PAAs). Two types of PPAs were employed. The first was obtained by reacting an equimolar mixture of oxydianiline (ODA) and pyromellitic dianhydride (PMDA) in dimethylactamide (DMAc) as solvent. The second was prepared using a mixture of ODA and 2,2-Bis(3-amino-4-hydroxyphenyl) hexafluoropropane (6F-OHDA) in molar ratio 9: 1, respectively and reacting with a stoichiometric amount of PMDA in DMAc. Polyamic acids were converted to polyimides and a sol-gel reaction proceeded simultaneously by heating the hybrid films to 300 degrees C. The hydroxyl groups from 6F-OHDA allows the secondary bonding between the polyimide and growing silica phase and thus retard the gross phase separation. Only the 10 mol% addition of 6F-OHDA in the polyimide chain resulted in a drastically different microstructure for the resulting hybrids. SEM, stress-strain analysis, temperature variation of storage and loss modulus, and thermal stability were used to characterize the hybrid materials. Properties of both types of hybrids have been compared and related to the two different types of structures of polyimides used in the preparation of the hybrids.

Nanostructured films of iron, tin and titanium oxides were grown on glass and quartz by gas phase decomposition of [Fe(OtBu)3]2, [Sn(OtBu)4] and [Ti(OiPr)4], respectively. Films obtained exhibit good adhesion and homogeneous morphology with structural features in the nanometer range. The influence of microstructure and phase on optical (α-Fe2O3 and Fe3O4), gas sensing (SnO2) and photocatalytic (TiO2) properties was systematically studied to explore the potential of these coatings for technological applications.

Yttrium aluminum garnet (YAG) nanopowders doped with high neodymium (Nd) content (3 at.%) were synthesized by the sol-gel processing of (I) alkoxide precursors and (II) metal chelates formed by complexing the cations with polyethylene glycol. A stoichiometric YAG composition was obtained following both procedures; however, the agglomeration of particles was significantly higher in glycolate synthesis, which shielded residual organics from oxidation (elemental analyses). Distribution of Nd3+ ions in the YAG matrix, as shown by the absorption of pump energy and photoluminescence spectra of Nd:YAG ceramics, was more homogeneous in alkoxide-derived powders. The segregation of Nd centers in the glycolate-derived sample was supported by the precipitation of a crystalline Nd2O3 phase (X-ray diffraction) during sintering. High-resolution absorption spectra (4I9/2(1)-> 4F9/2(1)) of the powders showed that a higher absorption cross-section of glycolate-derived powders is due to Nd3+-Nd3+ ion pairing, which leads to the quenching of photoluminescence. Owing to the better dispersion of optically active centers, the photoluminescence signal was found to be substantially enhanced in alkoxide-derived Nd:YAG ceramics.