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Schneider J.,University of Bremen | Ciacchi L.C.,University of Bremen | Ciacchi L.C.,Fraunhofer Institute for Manufacturing Engineering and Applied Materials Research
Journal of Chemical Theory and Computation | Year: 2011

The behavior of titanium implants in physiological environments is governed by the thin oxide layer that forms spontaneously on the metal surface and mediates the interactions with adsorbate molecules. In order to study the adsorption of biomolecules on titanium in a realistic fashion, we first build up a model of an oxidized Ti surface in contact with liquid water by means of extensive first-principles molecular dynamics simulations. Taking the obtained structure as reference, we then develop a classical potential to model the Ti/TiOx/water interface. This is based on the mapping with Coulomb and Lennard-Jones potentials of the adsorption energy landscape of single water and ammonia molecules on the rutile TiO2(110) surface. The interactions with arbitrary organic molecules are obtained via standard combination rules to established biomolecular force fields. The transferability of our potential to the case of organic molecules adsorbing on the oxidized Ti surface is checked by comparing the classical potential energy surfaces of representative systems to quantum mechanical results at the level of density functional theory. Moreover, we calculate the heat of immersion of the TiO 2 rutile surface and the detachment force of a single tyrosine residue from steered molecular dynamics simulations, finding good agreement with experimental reference data in both cases. As a first application, we study the adsorption behavior of the Arg-Gly-Asp (RGD) peptide on the oxidized titanium surface, focusing particularly on the calculation of the free energy of desorption. © 2010 American Chemical Society.

Schneider J.,University of Bremen | Colombi Ciacchi L.,University of Bremen | Colombi Ciacchi L.,Fraunhofer Institute for Manufacturing Engineering and Applied Materials Research
Journal of the American Chemical Society | Year: 2012

We present evidence that specific material recognition by small peptides is governed by local solvent density variations at solid/liquid interfaces, sensed by the side-chain residues with atomic-scale precision. In particular, we unveil the origin of the selectivity of the binding motif RKLPDA for Ti over Si using a combination of metadynamics and steered molecular dynamics simulations, obtaining adsorption free energies and adhesion forces in quantitative agreement with corresponding experiments. For an accurate description, we employ realistic models of the natively oxidized surfaces which go beyond the commonly used perfect crystal surfaces. These results have profound implications for nanotechnology and materials science applications, offering a previously missing structure-function relationship for the rational design of materials-selective peptide sequences. © 2011 American Chemical Society.

Enthaler S.,TU Berlin | Von Langermann J.,Max Planck Institute for Dynamics of Complex Technical Systems | Schmidt T.,Fraunhofer Institute for Manufacturing Engineering and Applied Materials Research
Energy and Environmental Science | Year: 2010

In search for future energy supplies the application of hydrogen as an energy carrier is seen as a prospective issue. However, the implementation of a hydrogen economy is suffering from several unsolved problems. Particularly challenging is the storage of appropriate amounts of hydrogen. In this context the utilization of carbon dioxide-formic acid for hydrogen storing is discussed. © The Royal Society of Chemistry 2010.

Simchi A.,Sharif University of Technology | Petzoldt F.,Fraunhofer Institute for Manufacturing Engineering and Applied Materials Research
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2010

Sintering response and phase formation during sintering of WC-Co/316L stainless steel composites produced by assembling of powder injection molding (PIM) parts were studied. It is shown that during cosintering a significant mismatch strain (>4 pct) is developed in the temperature range of 1080 °C to 1350 °C. This mismatch strain induces biaxial stresses at the interface, leading to interface delamination. Experimental results revealed that sintering at a heating rate of 20 K/min could be used to decrease the mismatch strain to <2 pct. Meanwhile, WC is decomposed at the contact area and the diffusion of C and Co into the iron lattice results in the formation of a liquid and MC and M6C carbides at 1220 °C. Spreading of the liquid accelerates the reaction, affecting the dimensional stability of the PIM parts. To prevent the reaction, surface oxidation of the cemented carbide followed by hydrogen reduction during sintering was examined. Although the amount of mismatch strain increased, formation of a metallic interface consisting of a W-Co alloy (45 to 50 at. pct Co) and a Co-rich iron alloy (18 at. pct Co) prevented the decomposition of WC and melt formation. It is also shown that the deposition of a thin Ni layer after thermal debinding decreases the mismatch stresses through melt formation, although interlayer diffusion causes pore-band formation close to the steel part. © 2009 The Minerals, Metals & Materials Society and ASM International.

Tamjid E.,Sharif University of Technology | Guenther B.H.,Fraunhofer Institute for Manufacturing Engineering and Applied Materials Research
Powder Technology | Year: 2010

Rheological behavior of agglomerated silver nanoparticles (~ 40 nm) suspended in diethylene glycol over a wide range of volumetric solids concentrations (φ{symbol} = 0.11-4.38%) was studied. The nanoparticle suspensions generally exhibited a yield pseudoplastic behavior. Bingham plastic, Herschel-Bulkley and Casson models were used to evaluate the shear stress-shear rate dependency. Analyzing the effect of silver concentrations on the yield stress and viscosity of the suspensions followed an exponential form, revealing an increase in the degree of interparticle interactions with increasing solid concentrations. Fractal dimension (Df) was estimated from the suspension yield stress and φ{symbol} dependence, and was determined as Df = 1.51-1.62 for the flocculated nanoparticle suspensions. This suggested that the suspension structure was probably dominated by the diffusion-limited cluster-cluster aggregation (DLCA) due mostly to the strong attractions involved in the interparticle potentials. Maximum solids concentration of the suspensions was determined to be φ{symbol}m = 11%. © 2009 Elsevier B.V. All rights reserved.

Trapp J.,Fraunhofer Institute for Manufacturing Engineering and Applied Materials Research | Trapp J.,TU Dresden | Kieback B.,Fraunhofer Institute for Manufacturing Engineering and Applied Materials Research | Kieback B.,TU Dresden
Acta Materialia | Year: 2013

The phase formation of carbides and borides during high-energy ball milling has been investigated by measuring the gas temperature inside the vial and by X-ray diffraction studies of specimens taken at different stages of the milling process. The formation mechanism changes from a gradual process to an instantaneous, explosion-like reaction with increasing milling intensity and enthalpy of product formation. Finally, a model was developed to describe the milling process, and to determine the peak temperatures that are reached in the powder particles during ball collisions as well as the microstructure evolution. Using an effective coefficient of diffusion and calculating the evolution of the continuously growing diffusion layer, it was possible to determine whether and when rapid phase formation occurs. The model was tested by reproducing the milling times needed for rapid phase formation inside the mill. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Koschek K.,Fraunhofer Institute for Manufacturing Engineering and Applied Materials Research
Composites Part A: Applied Science and Manufacturing | Year: 2015

Butanediol initiated poly(ε-caprolactone) (PCL) has recently been reported as a toughening agent for cationically curing cycloaliphatic epoxides providing plasticized thermosets with excellent properties (Lützen et al., 2013). In this contribution that promising toughening approach was applied for the first time for the development of novel natural fiber composites (NFC). NFCs based on conventional brittle thermosetting polymers often suffer from poor interfacial adhesion and stress cracking. Composites made up of the novel plasticized thermosets and woven flax fiber preserved the elastomer-like properties and increased tensile strength and elongation at break up to 60 MPa and 5%, respectively. Furthermore, PCL was shown not only to toughen the epoxide but also to modulate the affinity of the matrix to the fiber. In conclusion, improved interfacial adhesion and the resulting excellent mechanical properties of cationically curable NFCs were achieved by both interfacial crystallization and affinity. © 2014 Elsevier Ltd. All rights reserved.

Marzi S.,Fraunhofer Institute for Manufacturing Engineering and Applied Materials Research
European Physical Journal: Special Topics | Year: 2012

This paper shows and discusses results of the Tapered End-Notched Flexure (TENF) test, investigating the fracture behaviour of high-strength structural adhesive joints under shear loading. The TENF test has been previously applied to brittle joints by different authors and has been re-designed to be applicable to ductile adhesives in the presented work. Furthermore, the tests are performed at two velocities, a quasi-static and a dynamic one, to investigate rate effects on the fracture behaviour of the joint. All experimental work has been performed using the structural adhesive DOW Betamate 1496V. © 2012 EDP Sciences and Springer.

Merten C.,Fraunhofer Institute for Manufacturing Engineering and Applied Materials Research | Hartwig A.,Fraunhofer Institute for Manufacturing Engineering and Applied Materials Research
Macromolecules | Year: 2010

The structures of the helical chiral polymer poly(trityl methacrylate), PTrMA, in solid state and in chloroform solution are compared by using vibrational circular dichroism spectroscopy. The differences between the spectra are discussed in detail based on band assignments and density functional theory calculations. Therefore, VA and VCD spectra of oligomers of PTrMA were calculated. It is shown that in solution as well as in solid state the helical structure is maintained. Furthermore, it was possible to determine the helical screw sense of the dextrorotary enantiomer (+)-PTrMA to be left-handed. © 2010 American Chemical Society.

Fraunhofer Institute for Manufacturing Engineering and Applied Materials Research | Date: 2015-03-31

A metal casting method and a plastic injection molding method in which an insert is molded in molten material such that no molten material enters the interior of the insert. At the usage of a wire thread insert as insert this has the advantage that for example in an aluminum cast part thread holes can be produced already as part of the casting process. For this purpose, the present disclosure describes an the casting mold, the insert as well as the casting method.

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