TY - JOUR A1 - Orts Gil, Guillermo A1 - Natte, Kishore A1 - Drescher, Daniela A1 - Bresch, Harald A1 - Mantion, Alexandre A1 - Kneipp, J. A1 - Österle, Werner T1 - Characterisation of silica nanoparticles prior to in vitro studies: from primary particles to agglomerates N2 - The size, surface charge and agglomeration state of nanoparticles under physiological conditions are fundamental parameters to be determined prior to their application in toxicological studies. Although silica-based materials are among the most promising candidates for biomedical applications, more systematic studies concerning the characterisation before performing toxicological studies are necessary. This interest is based on the necessity to elucidate the mechanisms affecting its toxicity. We present here TEM, SAXS and SMPS as a combination of methods allowing an accurate determination of single nanoparticle sizes. For the commercial material, Ludox TM50 single particle sizes around 30 nm were found in solution. DLS measurements of single particles are rather affected by polydispersity and particles concentration but this technique is useful to monitor their agglomeration state. Here, the influence of nanoparticle concentration, ionic strength (IS), pH and bath sonication on the agglomeration behaviour of silica particles in solution has been systematically investigated. Moreover, the colloidal stability of silica particles in the presence of BSA has been investigated showing a correlation between silica and protein concentrations and the formation of agglomerates. Finally, the colloidal stability of silica particles in standard cell culture medium has been tested, concluding the necessity of surface modification in order to preserve silica as primary particles in the presence of serum. The results presented here have major implications on toxicity investigations because silica agglomeration will change the probability and uptake mechanisms and thereby may affect toxicity. KW - Silica KW - Toxicology KW - Agglomeration KW - BSA KW - Nanoparticles KW - Characterisation PY - 2011 U6 - https://doi.org/10.1007/s11051-010-9910-9 SN - 1388-0764 SN - 1572-896X VL - 13 IS - 4 SP - 1593 EP - 1604 PB - Springer AN - OPUS4-21179 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Hinrichs, R. A1 - Vasconcellos, M.A.Z. A1 - Österle, Werner A1 - Prietzel, Claudia T1 - A TEM snapshot of magnetite formation in brakes: the role of the disc's cast iron graphite lamellae in third body formation N2 - A cross-section sample of the friction film formed on top of a disc during a brake testing procedure against Polymer Matrix Composite pads was made using a Focused Ion Beam (FIB). The FIB-cut sampled the "third body" magnetite layer and the upper part of the cast iron disc containing a graphite flake. Images of the sample examined in a Energy Filtered Transmission Electron Microscope captured an instant view of the important role of the graphite flakes in magnetite formation, where few layer graphene batches interacted with the iron border promoting cracking and oxidation along the graphite–iron interface. The resulting nano-scale interlayer of magnetite and strongly disordered graphite formed a third body which yielded adequate brake performance. KW - Cast iron KW - Carbon KW - Graphite KW - Tribochemistry KW - Electron microscopy PY - 2011 U6 - https://doi.org/10.1016/j.wear.2010.11.008 SN - 0043-1648 VL - 270 IS - 5-6 SP - 365 EP - 370 PB - Elsevier B.V. CY - Amsterdam AN - OPUS4-23189 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Naghib Zadeh, Hamid A1 - Glitzky, Carsten A1 - Österle, Werner A1 - Rabe, Torsten T1 - Low temperature sintering of barium titanate based ceramics with high dielectric constant for LTCC applications N2 - The sintering temperature of BaTiO3 powder was reduced to 900 °C due to the ZnO-B2O3-Li2O-Nb2O5-Co2O3 addition. Excellent densification was achieved after sintering at 900 °C for 2 h. The low sintering temperature of newly developed capacitor materials allows a co-firing with pure silver electrodes. The dielectric constant and the temperature stability of the dielectric constant are strongly correlated with the composition of the ZnO-B2O3-Li2O additives. A high dielectric constant up to 3000 and a dielectric loss less than 0.024 were measured on multilayer capacitors sintered at 900 °C with silver inner electrodes. KW - BaTiO3 and titanates KW - Capacitors KW - Dielectric properties KW - LTCC PY - 2011 U6 - https://doi.org/10.1016/j.jeurceramsoc.2010.10.003 SN - 0955-2219 SN - 1873-619X VL - 31 IS - 4 SP - 589 EP - 596 PB - Elsevier Ltd. CY - Oxford AN - OPUS4-22886 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Österle, Werner A1 - Dmitriev, Andrey T1 - Functionality of conventional brake friction materials - Perceptions from findings observed at different length scales N2 - Automotive braking is based on dry friction between fixed pads and a rotating disc. Besides macroscopic thermo-physical properties, the development of topographic features on the mesoscopic scale and the nanostructure of the third body formed by wear processes, determine brake performance properties. Whereas modelling on the atomistic scale is suitable to understand mechanisms leading to nanocrystalline surface films, the properties of such films can be assessed best with a model based on movable cellular automata (MCA). It turned out that the presence of at least 10% of soft nanoinclusions is most essential in respect to smooth sliding conditions. It made no major difference whether graphite or copper particles were assumed as soft nanoinclusions. The third body material is not only the stuff which spreads over contact areas, but it also contributes to contact size by wear particle compaction and formation of secondary contact areas. The evolution of contact size is the major feature of mesoscopic modelling and thus it is capable to model and explain dynamic changes of the coefficient of friction (COF) during certain brake operations. Although it is still ambiguous in many cases which feature has the major impact on friction behaviour, the following conclusions can be drawn. The reinforcing ingredients of the pad material serve as primary contact sites and thus define the starting condition for mesoscopic simulations. A certain amount of wear is necessary to provide a third body which is capable to form secondary contact sites and friction layers screening the first body materials. The composition and nanostructure of the third body is important as well, because it determines the friction level and is responsible for smooth sliding conditions. KW - Nanostructure KW - Microstructure KW - Mesostructure KW - Macrostructure KW - Modelling KW - Simulation PY - 2011 U6 - https://doi.org/10.1016/j.wear.2010.11.035 SN - 0043-1648 VL - 271 IS - 9-10 SP - 2198 EP - 2207 PB - Elsevier B.V. CY - Amsterdam AN - OPUS4-24177 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Merk, Virginia A1 - Schulte, Franziska A1 - Rooch, Heidemarie A1 - Feldmann, Ines A1 - Dörfel, Ilona A1 - Österle, Werner A1 - Panne, Ulrich A1 - Kneipp, Janina T1 - Surface-enhanced Raman scattering with silver nanostructures generated in situ in a sporopollenin biopolymer matrix N2 - Silver nanoparticles were generated based on citrate reduction in the ultrastructure of the sporopollenin biopolymer of Ambrosia artemisiifolia (ragweed) and Secale cereale (rye). The nanoparticles enable the acquisition of SERS spectra and thereby a vibrational characterization of the local molecular structure of sporopollenin. PY - 2011 U6 - https://doi.org/10.1039/c0cc05326k SN - 0022-4936 SN - 0009-241x SN - 1359-7345 SN - 1364-548x N1 - Geburtsname von Merk, Virginia: Joseph, V. - Birth name of Merk, Virginia: Joseph, V. VL - 47 IS - 11 SP - 3236 EP - 3238 PB - Royal Society of Chemistry CY - Cambridge AN - OPUS4-23482 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Drescher, Daniela A1 - Orts Gil, Guillermo A1 - Laube, G. A1 - Natte, Kishore A1 - Veh, R.W. A1 - Österle, Werner A1 - Kneipp, Janina T1 - Toxicity of amorphous silica nanoparticles on eukaryotic cell model is determined by particle agglomeration and serum protein adsorption effects N2 - Cell cultures form the basis of most biological assays conducted to assess the cytotoxicity of nanomaterials. Since the molecular environment of nanoparticles exerts influence on their physicochemical properties, it can have an impact on nanotoxicity. Here, toxicity of silica nanoparticles upon delivery by fluid-phase uptake is studied in a 3T3 fibroblast cell line. Based on XTT viability assay, cytotoxicity is shown to be a function of (1) particle concentration and (2) of fetal calf serum (FCS) content in the cell culture medium. Application of dynamic light scattering shows that both parameters affect particle agglomeration. The DLS Experiments verify the stability of the nanoparticles in culture medium without FCS over a wide range of particle concentrations. The related toxicity can be mainly accounted for by single silica nanoparticles and small agglomerates. In contrast, agglomeration of silica nanoparticles in all FCS-containing media is observed, resulting in a decrease of the associated toxicity. This result has implications for the evaluation of the cytotoxic potential of silica nanoparticles and possibly also other nanomaterials in standard cell culture. KW - Agglomeration KW - Cytotoxicity KW - Fibroblast cells KW - Serum proteins KW - Silica nanoparticles PY - 2011 U6 - https://doi.org/10.1007/s00216-011-4893-7 SN - 1618-2642 SN - 1618-2650 VL - 400 IS - 5 SP - 1367 EP - 1373 PB - Springer CY - Berlin AN - OPUS4-23678 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -