In peel, tests between polycarbonate/polyethersulfone (PC/PES) blends with different compositions and thermoplastic polyurethane (TPU) films with differ-ent thicknesses a large decrease in energy release rate G(c) is observed when the PC/PES blends formed a co-continuous structure. With SEM analysis, XRD measurements, selective PC etching of failed samples, and finite element modeling of the stress distributions in the co-continuous region this fracture behavior can be explained. It is caused by the interplay between the formation of the main crack in the process zone and the size and density of microcracks in the energy dissipation zone. While the pure components PC and PES exhibit good adhesion to the TPU, the immiscibility of PC and PES causes the steady decrease of G(c) with increasing volume fraction of the minor phase.

The degradation mechanism of human trabecular bone harvested from the central part of the femoral head of a patient with a fragility fracture of the femoral neck under conditions of senile osteoporosis was investigated by high-resolution electron microscopy. As evidenced by light microscopy, there is a disturbance of bone metabolism leading to severe and irreparable damages to the bone structure. These defects are evoked by osteoclasts and thus podosome activity. Podosomes create typical pit marks and holes of about 300–400 nm in diameter on the bone surface. Detailed analysis of the stress field caused by the podosomes in the extracellular bone matrix was performed. The calculations yielded maximum stress in the range of few megapascals resulting in formation of microcracks around the podosomes. Disintegration of hydroxyapatite and free lying collagen fibrils were observed at the edges of the plywood structure of the bone lamella. At the ultimate state, the disintegration of the mineralized collagen fibrils to a gelatinous matrix comes along with a delamination of the apatite nanoplatelets resulting in a brittle, porous bone structure. The nanoplatelets aggregate to big hydroxyapatite plates with a size of up to 10 x 20 μm2. The enhanced plate growth can be explained by the interaction of two mechanisms in the ruffled border zone: the accumulation of delaminated hydroxyapatite nanoplatelets near clusters of podosomes and the accelerated nucleation and random growth of HAP nanoplatelets due to a nonsufficient concentration of process-directing carboxylated osteocalcin cOC.

Formation of regularly structured silica valves of various diatom species is a particularly fascinating phenomenon in biomineralization. Intensive investigations have been devoted to elucidate the formation mechanisms of diatom valve structures. Phase-separation of species-specific organic molecules has been proposed to be involved in pattern formation, where the evolving organic molecule structures serve as template for silica formation. In the present work, using a continuum approach, we investigate the conditions under which silica structures of high regularity can develop within a phase separation model. In relation to previously reported in vitro experiments of silica formation, which revealed the important role of phosphate ions in the self-assembly of organic molecules, we propose a model where phase separation is coupled with a chemical reaction. We analyze the impact of the reaction of phosphate ions with organic molecules on the appearing morphology of the organic template. Two- and three-dimensional simulations of the development of regular stationary patterns are presented. The influence of a confined geometry and an interaction of organic molecules with the walls on pattern formation is also addressed. We expect that our approach will be relevant for experimental studies aiming at inducing structure formation under controlled in vitro conditions.

Understanding the diffusion of lithium ions in electrode materials for lithium ion batteries is of great importance for their knowledge-based optimization and development of novel materials and cell designs. The galvanostatic intermittent titration technique (GITT) is widely applied in battery research to study the diffusion of lithium in anode and cathode materials depending on the degree of lithiation. While transport properties of electrode materials at high and ambient temperatures are largely available, low temperature diffusion and rate coefficients are hardly reported in the literature and vary by orders of magnitude for identical active materials. Herein, we demonstrate and discuss several challenges and pitfalls in the application and evaluation of GITT measurements for determining the effective chemical lithium ion diffusion coefficient in lithium insertion electrodes, which become especially important at low temperature. This includes theoretical considerations and an experimental analysis of the promising cathode material LiNi0.5Co0.2Mn0.3O2 (NCM523) in the wide temperature range of −40 °C to 40 °C. We show how the choice of experimental conditions for the GITT measurements and of the subsequent mathematical evaluation significantly influence the derived diffusion coefficient. The results suggest that the large scattering of reported values of the diffusion coefficient could be caused by the use of different evaluation procedures. Simple calculation methods appear to be less suited the lower the temperature is. It is shown that the complementary use of GITT and EIS supplemented by detailed knowledge of the microstructure of the electrode significantly improves the accuracy of determining the diffusion coefficient.

Diatoms are a significant group of algae displaying a sizeable morphological diversity, whose underlying structure arises from nanopatterned silica. Extensive experimental evidence suggests that a delicate interplay between various organic components and polysilicic acid plays a crucial role in biosilica mineralization. Thus, gaining insight into the properties of this organic–inorganic interface is of great interest in understanding the mechanisms controlling biosilica formation over different length scales. In this work, we use all-atom Molecular Dynamics simulations to investigate the aggregation behavior of polysilicic acid and silica nanoparticles in solution in the presence of protonated long-chain polyamines with a focus on the nature of the driving forces mediating the organic–inorganic aggregation process. Our results show that electrostatic forces between organic and inorganic species are the dominant interaction responsible for largely preserving the structural integrity of the organic–inorganic aggregates in solution. Thus, aggregates involving electrically neutral polysilicic acid are fully dissolved in an aqueous environment, since hydrogen bonding and van der Waals interactions turn out to be not strong enough to keep the aggregates together. Our main simulation results are in qualitative agreement with in vitro experiments, so that we expect they can contribute to shedding light on the initial stages of biosilica mineralization in diatoms.

The interaction of additives and ions with the copper surface plays a crucial role in the copper electroplating process. In this work, the interaction of the additives polyethylene glycol (PEG) and bis(3-sulfopropyl)-disulfide (SPS) as well as of chloride with the Cu(111) surface is considered within the framework of density functional theory. In the presence of water, the adsorption energy of chloride diminishes by about 1 eV compared to the case in vacuum. The activation barrier for chloride desorption was found to be 0.8 eV. Simulations of the deposition of copper atoms on a Cl-covered copper surface revealed that Cl atoms are always displaced to the surface. Calculations of adsorption energies of additives in vacuum indicated that the accelerator molecule SPS is bound stronger to Cu(111) than the suppressor molecule PEG. A comparatively strong adsorption of additives was found on a copper surface covered with a Cl–Cu mixed layer. Investigation of the dynamics of additives on Cu(111) by means of first principles molecular dynamics revealed an occasional spontaneous decomposition of an SPS molecule into two MPS molecules.

For manufacturing copper interconnects by the damscence technique, electrochemical deposition of copper on patterned sustrates requires several additives to achieve compact filling of trenches and vias, where chloride ions play a crucial role. In the highly acidic electrolyte, adsorption of chloride ions on copper is expected to compete with the adsorption of hydrogen, depending on the copper electrode potential. We propose a general phenomenological model of the coadsorption of two ion species which is supported by DFT calculations and show how the adsorption of one species can be described by the common Langmuir model with rescaled parameters depending on the concentration of the second species. Regarding the Cl- -H+-system, corresponding model parameters are estimated by fitting radio tracer measurements of the chloride adsorption on copper reported in the literature. The data suggest that in a highly acidic solution (pH approximate to 0) the saturation surface density of chloride depends strongly on the electrode potential. With variation of the potential E-SHE from -0.4 to +0.2 V, the saturation density changes by a factor of four. Within our model, such a potential dependence of the saturation density is explained by the presence of adsorbed hydrogen. (C) The Author(s) 2018. Published by ECS.

Additives play an important role in electrochemical deposition and understanding their working mechanism is a great challenge. In cyclic voltammetry measurements of copper deposition, a complex hysteresis behavior is ubiquitously observed. In previous models a common assumption to explain the hysteresis is the consumption of additives during copper deposition. However, second-ion mass spectrometry measurements often detected comparatively low levels of impurities in deposits. We proposed recently an alternative mechanism for explaining hysteresis without invoking additive consumption. By assuming for instance a conformation change in the adsorbed PEG layer and an additional activation of additive desorption by copper deposition, the new model can reproduce characteristic features of cyclic voltammograms measured under vastly different conditions and exhibiting pronounced hysteresis. In parallel to that, we examined experimentally the process behavior of the additives PEG (polyethylene glycol) and chloride ions over a wide range of parameters relevant for production-like conditions. Moreover, we fitted crucial parameters of our model from the experimental data. The quantitative agreement of performed simulations of CV scans with the measured scans demonstrates the quantitative predicting power of the proposed model. Equipped with the determined parameter set, the model may help to optimize the copper plating process in industrial applications.

Additives play an important role in electrochemical deposition and understanding their working mechanism is a great challenge. In cyclic voltammetry measurements of copper deposition, hysteresis is ubiquitously observed. Correct prediction of hysteresis behavior is an important test for deposition models. In previous models, including poly(ethylene glycol) (PEG) and chloride ions as additives, a common assumption to explain the hysteresis is the consumption of additives during copper deposition. However, second-ion mass spectrometry measurements often detected comparatively low levels of impurities in deposits. Therefore, we propose here an alternative mechanism for explaining hysteresis curves without invoking additive consumption. Essential ingredients of our models are: (i) a strongly nonlinear dependence of the maximal possible PEG coverage on the chloride coverage on the copper surface, (ii) a nonlinear dependence of the deposition current on the PEG surface coverage, and (iii) an additional activation of the desorption of additives with increasing copper deposition current. We demonstrate that our model reproduces characteristic features of cyclic voltammograms measured under vastly different conditions and exhibiting pronounced hysteresis. Furthermore, simulations are compared well to PEG adsorption/desorption experiments with varying additive concentrations. The proposed model may serve to describe deposition situations with negligible additive consumption. (C) 2017 The Electrochemical Society. All rights reserved.

Thermal management is one of the crucial issues in the development of magnetocaloric refrigeration technology for application. In order to ensure optimal exploitation of the materials “primary” properties, such as entropy change and temperature lift, thermal properties (and other “secondary” properties) play an important role. In magnetocaloric composites, which show an increased cycling stability in comparison to their bulk counterparts, thermal properties are strongly determined by the geometric arrangement of the corresponding components. In the first part of this paper, the inner structure of a polymer-bonded La(Fe, Co, Si)13-composite was studied by X-ray computed tomography. Based on this 3D data, a numerical study along all three spatial directions revealed anisotropic thermal conductivity of the composite: Due to the preparation process, the long-axis of the magnetocaloric particles is aligned along the xy plane which is why the in-plane thermal conductivity is larger than the thermal conductivity along the z-axis. Further, the study is expanded to a second aspect devoted to the influence of particle distribution and alignment within the polymer matrix. Based on an equivalent ellipsoids model to describe the inner structure of the composite, numerical simulation of the thermal conductivity in different particle arrangements and orientation distributions were performed. This paper evaluates the possibilities of microstructural design for inducing and adjusting anisotropic thermal conductivity in magnetocaloric composites.

Understanding the molecular interactions between inorganic phases such as silica and organic material is fundamental for chromatographic applications, for tailoring silica-enzyme interactions, and for elucidating the mechanisms of biomineralization. The formation, structure, and properties of the organic/inorganic interface is crucial in this context. Here, we investigate the interaction of selectively 13C-labeled choline with 29Si-labeled monosilicic acid/silica at the molecular level. Silica/choline nanocomposites were analyzed by solid-state NMR spectroscopy in combination with extended molecular dynamics (MD) simulations to understand the silica/organic interface. Cross-polarization magic angle spinning (CP MAS)-based NMR experiments like 1H-13C CP-REDOR (rotational-echo double resonance), 1H-13C HETCOR (heteronuclear correlation), and 1H-29Si-1H double CP are employed to determine spatial parameters. The measurement of 29Si-13C internuclear distances for selectively 13C-labeled choline provides an experimental parameter that allows the direct verification of MD simulations. Atomistic modeling using classical MD methodologies is performed using the INTERFACE force field. The modeling results are in excellent agreement with the experimental data and reveal the relevant molecular conformations as well as the nature and interplay of the interactions between the choline cation and the silica surface. Electrostatic interactions and hydrogen bonding are both important and depend strongly on the hydration level as well as the charge state of the silica surface.

Photocatalytic degradation of organic components in water by means of TiO2 nanosuspensions under ultraviolet (UV) irradiation represents an efficient method for water purification. In the present paper, a modeling approach is proposed to simulate the involved kinetic processes based on the Langmuir–Hinshelwood mechanism. The extended model also includes the formation of intermediate organic components either by an incremental degradation mechanism or by a fragmentation mechanism. Model parameters were estimated from comparison with experimental findings. To demonstrate these models, adsorption and degradation experiments were performed using the antibiotic ciprofloxacin and the dye methylene blue as organic compounds and TiO2 and ZnO as photocatalytic materials. By comparing our simulations with concentration measurements, we found that the adsorption of organic molecules on the surface of the photocatalyst was rate determining at an irradiation intensity of about 20Wm−2. The derived adsorption rates for ZnO were considerably higher than those for TiO2. The calculated concentration evolution of intermediates as well as the TOC evolution are discussed for different model assumptions with respect to their desorption rates from the photocatalyst surface.

For assessing mechanical properties of osteoporotic bone, biomechanical testing combined with in silico modeling plays a key role. The present study focuses on microscopic mechanical bone properties in a rat model of postmenopausal osteoporosis. Female Sprague–Dawley rats were (1) euthanized without prior interventions, (2) sham-operated, and (3) subjected to ovariectomy combined with a multi-deficiencies diet. Rat vertebrae (corpora vertebrae) were imaged by micro-CT, their stiffness was determined by compression tests, and load-induced stress states as well as property changes due to the treatment were analyzed by finite-element modeling. By comparing vertebra stiffness measurements with finite-element calculations of stiffness, an overall microscopic Young’s modulus of the bone was determined. Macroscopic vertebra stiffness as well as the microscopic modulus diminish with progression of osteoporosis by about 70 %. After strong initial changes of bone morphology, further decrease in macroscopic stiffness is largely due to decreasing microscopic Young’s modulus. The micromechanical stress calculations reveal particularly loaded vertebra regions prone to failure. Osteoporosis-induced changes of the microscopic Young’s modulus alter the fracture behavior of bone, may influence bone remodeling, and should be considered in the design of implant materials.

Here we present electrochemically grown ultrathin platinum nanowires and demonstrate that their morphology and crystalline structure can be tuned by the waveform of the alternating voltage applied to the microelectrodes. The structure of the nanowires was analyzed by scanning and transmission electron microscopy. The voltage signal, applied to grow the nanowires, consisted of several Fourier components of a square-shaped wave. We observed that, depending on the number of Fourier components, the morphology of the nanowires changed from branched dendritic-like patterns to straight wires and the wire crystallinity changed from polycrystalline to highly oriented growth with the [111] direction of platinum crystallites along the nanowire axis. We propose a simple model to explain this intriguing observation.

Aiming at a better quantitative understanding of the fundamental mechanisms that cause heat evolution in lithium ion batteries, theoretical modeling of the temperature evolution was performed associated with in-operando temperature measurements across the interfaces of a single lithium ion battery cell. For that purpose, an experimental setup has been developed at the Fraunhofer IKTS. The cylindrical electrode arrangement and the positioning of the thermocouples at specific interfaces within the lithium ion cell is illustrated in the figure. The success of this experimental approach has recently been demonstrated [1]. The present modeling is based on Newman's pseudo-2D model [2], extended however by including a radial spatial dependence of the electrochemical processes and SoC-dependent material properties. To evaluate the reliability of the electrochemical modeling, simulations of GITT experiments were compared with corresponding measurements using a 3-electrode arrangement. Calculations of the electric potential and current densities within the cell during charging and discharging yield the spatially resolved heat-source densities. The simulations enable the comparison of different contributions to the local heat generation. Reversible heat due to entropy changes, irreversible reaction heat, and ohmic heating within the electrode materials and the electrolyte are included in the temperature model as a function of the SoC for a wide range of charge/discharge rates. The effect of parameter variations on the temperature evolution has been extensively explored, particularly in view of different reported material properties [3]. Differences in the heat generation within the cathode, separator, and anode as a function of time, charge/discharge rate and SoC were successfully identified both theoretically and experimentally. Generally, the numerical results and the measurements reveal the significance of reversible heat effects due to electrochemical reactions under near equilibrium conditions, whereas Joule heating becomes important at high current densities. In-operando measurements allow time-resolved as well as SoC-dependend study of key parameters for the numerical simulation. The present work magnificently show the strong relation between the fundamental electrochemical processes and the resulting heat impact. [1] C. Heubner, M. Schneider, C. Lämmel, U. Langklotz, A. Michaelis; In-operando temperature measurement across the interfaces of a lithium-ion battery cell; Electrochim. Acta, 113 (2013) 730-734. [2] M. Doyle, T.F. Fuller, J. Newman; Modeling of galvanostatic charge and discharge of the lithium/polymer/insertion cell; J. Electrochem. Soc. 140 (1993) 1526-1533. [3] M. Park, X. Zhang, M. Chung, G.B: Less, A.M. Sastry; A review of conduction phenomena in Li-ion batteries; J. Power Sources 195 (2010) 7904-7929

The complex reaction mechanism of methane combustion on the PdO(100) surface is investigated within the framework of density functional theory. Driving forces and activation energies for the dissociative adsorption of methane and for the successive dehydrogenation of adsorbed hydrocarbons are calculated. Energy barriers of some of the dehydrogenation reactions are comparable to the barrier for the dissociative adsorption of methane, contrary to what is often assumed. Moreover, we find that reaction barriers for the early formation of C–O bonds are much lower than those for the complete dehydrogenation of CH4. In particular, reaction of oxygen molecules from the gas phase with suitable configurations of adsorbed H and CH3 can efficiently produce water and CH2O as oxidation products. Along this reaction path, the highest barrier is indeed given by the first dehydrogenation reaction.

The key properties of a successful cathode material, such as the structural stability during delithiation, the battery voltage, and the Li mobility, were investigated for Al-doped Li–Mn–Ni oxide structures, using density-functional theory and the nudged-elastic band method. The rhombohedral layered structure of LiMn0.5Ni0.5O2 with zigzag and flower arrangements of transition metal atoms as well as the monoclinic structure of Li(Li1/6Ni1/6Mn2/3)O2 were used as base structures. A stabilizing effect of Al-doping was found for all partially lithiated systems considered. The derived battery voltages at zero temperature are generally enhanced by Al-doping. The calculated activation energies for Li jumps suggest slower Li mobility. The Al-doped Li-rich monoclinic structure seems to be most promising as a cathode material because of a comparatively high battery voltage.

Based on experimental studies on tube formation during self-assembly of bacterial surface (S)-layers, a mechanistic model for describing the underlying basic mechanisms is proposed and the effect of process parameters on growth velocity and tube radius is investigated. The S-layer is modeled as a curved sheet with discrete binding sites for the association of monomers distributed along the S-layer edges. Reported changes of the tube radius owing to genetic protein modifications are explained within the framework of continuum mechanics. S-layer growth velocity and shape development are analyzed by Monte Carlo simulation in their dependence on the attachment and detachment frequencies of monomers at the S-layer. For curved S-layer patches, a criterion for the formation of S-layer tubes is derived. Accordingly, tubes can form only within a certain range of the initial monomer concentration. Furthermore, the effect of calcium ion concentration on tube formation is discussed, including recent experimental findings on the calcium effect.

The force balance between the extracellular microenvironment and the intracellular cytoskeleton controls the cell fate. We report a new (to our knowledge) mechanism of receptor force control in cell adhesion originating from friction between cell adhesion ligands and the supporting substrate. Adherent human endothelial cells have been studied experimentally on polymer substrates noncovalently coated with fluorescent-labeled fibronectin (FN). The cellular traction force correlated with the mobility of FN during cell-driven FN fibrillogenesis. The experimental findings have been explained within a mechanistic two-dimensional model of the load transfer at focal adhesion sites. Myosin motor activity in conjunction with sliding of FN ligands noncovalently coupled to the surface of the polymer substrates is shown to result in a controlled traction force of adherent cells. We conclude that the friction of adhesion ligands on the supporting substrate is important for mechanotransduction and cell development of adherent cells in vitro and in vivo.