Publikationen

The solvothermal reactions of Ti(OiPr)4 in alcohol using ionic liquid as additive were investigated. In the presence of [BMIM][Cl], [BMIM][Br], [BMIM][NTf2], [BMIM][SO3Me], [BMIM][SO4Me], or [BMIM][OTf] (BMIM = 1-Butyl-3-methylimidazolium), pure anatase nanoparticles were obtained. The controlled hydrolysis of Ti(OiPr)4 in the presence of ionic liquids to form titanium oxo clusters plays a key role in the formation of anatase nanostructures, and ionic liquids can be repeatedly used to synthesise anatase nanoparticles. However, in the presence of [BMIM][PF6], [BMIM]2[Ti(OH)6] was obtained by an anion exchange reaction.

The hydrolysis reactions of Ti(OiPr)4 in the presence of different ionic liquids using ethanol as solvent were investigated. The reaction in the presence of [BMIM][BF4] gave rise to the anion exchange reaction product [BMIM]2[Ti(OH)6] in moderate yield. On the contrary, Ti7O4(OEt)20 was obtained in ionic liquids with other anions. The anion exchange reaction has a broad capacity for group functionalization. It can be used to synthesize both imidazolium and pyridium [Ti(OH)6]2− salts. In contrast, under the similar reaction conditions, the reactions of zirconium alcoholate gave rise to [Zr(OH)5]− or [Zr(OH)6]2− intermediates depending on the counter cations. Under the solvothermal reaction conditions, [PF6]− based ionic liquids can also undertake the similar anion exchange reactions.

Tin oxide (SnO2) nanowires grown by chemical vapor deposition were modified by Ar/O2 plasma treatment through preferential etching of the lattice oxygen atoms, which produced nonstoichiometric surface compositions that imparted a manyfold higher sensitivity toward gas absorption on such surfaces. Microstructures of as-grown and plasma-treated SnO2 nanowires confirmed the gradual change in the chemical composition and morphologies. Surficial disorder caused by the bombardment of argon and oxygen ions present in the plasma was visible as a disordered overlayer in high-resolution TEM micrographs, when compared to single crystalline s-grown SnO2 nanowires. Gas-sensing experiments on modified SnO2 nanostructures showed higher sensitivity for ethanol gas at lower operating temperatures and exhibited an improved transduction response toward changing gas atmospheres, attributed to the increased concentration or oxygen vacancies on the surface or SnO2 nanowires. Modulation of surface chemistry was also supported by photoluminescence and X-ray photoemission spectroscopy studies.

The branched tripodal chloro-methyl-siloxanes of the general formula tBuSi[ {OSiMe2}yOSiMe3-xCl3]3 [x = 0-3; y = 0-2] were synthesized, starting with tert-Butyl-trisilanol (1). The treatment of 1 with the chloro-methyl-silanes (Me3-xSiClx+1) (x = 0-3) in the presence of triethylamine leads to the compounds tBuSi(OSiMe2Cl)3 (2), tBuSi(OSiMeCl2)3 (3) and tBuSi(OSiCl3)3 (4), The siloxanes 2-4 are colourless oily liquids, which can be purified by distillation, Their yields decrease with the number of chloro substituents. In the reaction of compound 2 with three equivalents of water the silantriol tBuSi(OSiMe2OH)3 (5) is generated which is used to create the branched tripodal chloro-methyl-siloxanes tBuSi(OSiMe2OSiMe3)3 (6), tBuSi(OSiMe2OSiMe2Cl)3 (7), tBuSi(OSiMe2OSiMeCl2)3 (9) and tBuSi(OSiMe2OSiCl3)3 (10). Compound (7) is only a side product with a yield of 25 %. The cyclic tBuSi[{(OSiMe2)2Cl}(OSiMe2)3O] (8) can be isolated and characterised. The transformation of the compound tBuSi(OSiMe2OSiMe2Cl)3 (7) into the trisilanol tBuSi(OSiMe2OSiMe2OH)3 (11) allows to prepare the tripodale siloxane tBuSi(OSiMe2OSiMe2OSiMe3)3 (12) in good yields. The reaction of tBuSi(OSiMe2Cl)3 (2) with tert-butyl trisilanol 1 leads to the formation of bicyclic tBuSi(OSiMe2O)3SitBu (13). An X-ray structure determination on 13 reveals a [3.3.3]-bicycle with, a C3 axis, which crystallizes in the cubic crystal system in the space group Pa3̄¯. The reported compounds 2-13 were characterised by NMR- and IR spectroscopy (5, 11) and show correct elemental analyses. The 29SiNMR-data of the compounds show interesting trends with respect to the Si-O chain length and the chloro substistuents.

To evaluate mechanical properties by means of nanoindentation, information on the contact area is crucial. However, the contact area is not directly accessible in experiments and is usually calculated according to the Oliver and Pharr procedure, which turned out to be unsatisfying when applied to viscoelastic materials like polymers. In this study, complementary in situ indentation testing and finite element analysis (FEA) were performed on silicone elastomers. Through this combination of techniques, several individual error sources in the conventional contact area determination have been identified and quantified. For shallow penetrations, contact areas after Oliver and Pharr were up to 40% smaller than the in situ testing results; for larger penetrations, the contact size was overestimated by approximately 6%. The deviations of the resulting mechanical properties were approximately 10%. Viscoelastic effects could be captured if dynamic indentation testing was performed.

The mechanics of frictional attachment between surfaces with pillars, inspired by the head fixation system of dragonflies, is analyzed. The system consists of two surfaces of interdigitating pillars held together through friction, as by the densely packed bristles of two brushes when pressed together. The adhesive strength of the system is promoted by high elastic modulus, high friction coefficient, large aspect ratio, and dense packing of the fibers. However, the design is limited by the compressive buckling, the compressive indentation or cracking of the contacting pillars, yielding in shear or similar mechanisms that limit the achievable friction stress, and tensile failure of the pillars upon pull-out. Maps, which summarize the strength of the adhesive system and the failure limits and illustrate the trade-off among the design parameters, are presented. Case studies for steel, nylon, and ceramic pillars show that useful strength can be achieved in such attachments; when buckling during assembly and contact failure can be avoided, adhesive performance as high as 30% of the tensile strength of the pillar material may be possible.

Nanoscaled so called indium tin oxide In2O3:Sn (ITO) with a specific BET surface area of 50 m2/g to 60 m2/g was prepared via an electrochemical method in an aqueous system containing ammonium acetate as conductive salt. As an intermediate product of the synthesis nanocrystalline In(OH)3 is obtained which serves as a precursor for the subsequent calcinations accompanied by tin doping resulting in ITO powders with various tin concentrations. Its phase transitions and the reduction behaviour of hydroxide to oxide during the calcination process in air flow and forming gas atmosphere of N2 to H2 ratio of 95 to 5 respectively, have been investigated by high temperature X-ray diffraction, TG/DSC/MS, HRTEM and SEM analysis. Depending on the atmosphere dehydration of tin doped In(OH)3 started at 150 °C, cubic ITO solid solution formed between 190 °C and 300 °C. The total weight loss of the hydroxide of approx. 21% occurred mainly below 360 °C and the burn-out of organic components mainly between 308 °C and 316 °C. The results of DSC and MS analyses were in good agreement with the results of the X-ray diffraction. In addition, the products have been characterized by EDX associated with TEM, XPS, ICP-AES, BET analysis and 119Sn Mössbauer spectroscopy. Completely reacted samples of ITO have been processed to pellets, calcined and sintered in the temperature range between 900 °C and 1100 °C and characterized by measurements of the electrical conductivities of bulk and surface in the reduced as well as in the oxidized state giving values up to 1400 Scm−1.

Symmetric and asymmetric diffusers with a directional diffusion property were both fabricated based on a photopolymerizable hologram material using an ionic liquid as an additive. The diffusion property can be regulated by changing the concentration of the ionic liquid. The fiber structure, the surface-relief structure, and the formation of nanoparticles led to the directional diffusion property of the diffuser.

We study conservation and balance laws of linear three-dimensional elasticity in terms of stress function tensors of first and second order. Such conservation and balance laws are sometimes called dual ones. The dual Eshelby stress tensor, angular momentum tensor and scaling flux of elasticity in stress space are derived within the framework of Noether's theorem on variational principles. Certain conservation and balance (or broken conservation) laws of translational, rotational, and dilatational symmetries including inhomogeneities, elastic anisotropy, dislocations, and incompatibilities are found. The conserved and non-conserved dual J, L, and M integrals are derived and discussed. Also we give the conservation and balance laws corresponding to the gauge symmetries and the addition of solutions. From the addition of solutions we derive reciprocity theorems for the stress functions of first and second order. Explicit formulae for the configurational forces, moments, and work terms in terms of stress function tensors are formulated.

To bridge soft biological materials and hard inorganic materials is an interdisciplinary scientific challenge. Despite of experimental difficulties, the deposition of native biological membranes on supports is a straightforward strategy. This review provides an overview of advances in the fabrication and characterization of native biological membranes on planar polymer supports and micro-particles.