This manuscript reports investigation conducted on room temperature ionic liquids (RTILs) C1CnImNTf2/n=4, 6 in order to use it as electrolyte solvent in lithium ion battery. The ionic conductivity, viscosity, ion self-diffusion coefficients, and electrochemical stability in C1CnImNTf2 are presented. A solution of C1CnImNTf2/n=4, 6 containing 1.6 mol.L-1 of LiNTf2 has been used as the electrolyte in a Li-ion battery with graphite and LiFePO4 as respectively negative and positive active materials. [Li][C1C6Im][NTf2] shows the best cycling performance: a capacity up to 120 mAh.g-1 at C/10 rate at 25°C.

The atomic and electronic structures of multilayer graphene on a monolayer boron nitride (MLBN) have been investigated by using the pseudopotential method and the local density approximation (LDA) of the density functional theory (DFT). We show that the LDA energy band gap can be tuned in the range 41-278 meV for a multilayer graphene by using MLBN as a substrate. The dispersion of the π/π* bands slightly away from the K point is linear with the electron speed of 0.9×106 and 0.93×106 for graphene (MLG)/MLBN and ABA trilayer graphene (TLG)/MLBN systems, respectively. This behaviour becomes quadratic with a relative effective mass of 0.0021 for the bilayer graphene (BLG)/MLBN system. The calculated binding energies are in the range of 10-43 meV per C atom.

Proteins are complex, yet elegant, machines fine-tuned by evolution to properly fulfill a variety of tasks in the crowded cellular environment. These are, however, very challenging numerically due to their dimension, number of degrees of freedom and the wide range of relevant time scales. With aging, some proteins misfold and form harmful amyloid aggregates associated with multiple neurodegenerative diseases, and in particular Alzheimer’s, which challenge our society today. Here, I present the coarse-grained OPEP (Optimized Potential for Efficient peptide structure Prediction) force field and what we can learn from OPEP simulations to get insights into the self-assembly of amyloid peptides.

This paper reports on mechanical characterization of electrospun tissue scaffolds formed from varying blends of collagen and human tropoelastin. The electrospun tropoelastin-based scaffolds have an open, porous structure conducive to cell attachment and have been shown to exhibit strong biocompatibility, but the mechanical character is not well known. Mechanical properties were tested for scaffolds consisting of 100% tropoelastin and 1:1 tropoelastin-collagen blends. The results showed that the materials exhibited a three order of magnitude change in the initial elastic modulus when tested dry vs. hydrated, with moduli of 21 MPa and 0.011 MPa respectively. Noncrosslinked and crosslinked tropoelastin scaffolds exhibited the same initial stiffness from 0 to 50% strain, and the noncrosslinked scaffolds exhibited no stiffness at strains >∼50%. The elastic modulus of a 1:1 tropoelastin-collagen blend was 50% higher than that of a pure tropoelastin scaffold. Finally, the 1:1 tropoelastin-collagen blend was five times stiffer from 0 to 50% strain when strained at five times the ASTM standard rate. By systematically varying protein composition and crosslinking, the results demonstrate how protein scaffolds might be manipulated as customized biomaterials, ensuring mechanical robustness and potentially improving biocompatibility through minimization of compliance mismatch with the surrounding tissue environment. Moreover, the demonstration of strain-rate dependent mechanical behavior has implications for mechanical design of tropoelastin-based tissue scaffolds.

Diffusion brazing is a potential method to repair parts made from TiAl-alloys. Two different brazing materials with varying contents of titanium, iron and nickel were investigated. The phases present in the brazed zone were identified by high energy X-ray diffraction (HEXRD) at the material science beamline HEMS at the PETRA III synchrotron facility at DESY in Hamburg, Germany, and the microstructure was characterised by scanning electron microscopy (SEM). The braze zone itself is composed of one to two transitional layers from the substrate material to the middle of the joint. Near the substrate material the phase constitution reassembles a TiAl-alloy while the middle of the joint is similar to α/β-titanium alloys. Besides phases commonly encountered in TiAl-alloys such as γ, α2 and β, additional phases, which are related to the presence of nickel or iron as melting point depressing elements are present. The microstructure of the brazed zone changes significantly during a subsequent heat treatment.

The internal micro/nano-structure of anisotropically oriented polymer/CNTs composites determines their macroscopic properties. However, the connections between the two are not fully understood. The varying of CNT concentration, preparation method, and a thermodynamic parameter (e.g. temperature) can all play interconnected role. In this work, the macroscopic electrical conductivity was measured perpendicular to the film thickness of an insulating polymer (isotactic PolyPropylene, iPP) and a nano-composite of iPP with 5 weight percent of CNT. The thin films studied were sheared (anisotropically nano-structured) and non-sheared (with random internal structure). In general the effect of melt shearing induces anisotropy on the electrical transport properties of the iPP/CNT films in directions parallel and perpendicular to the direction of orientation. Our results show that for the pure iPP, resistivity slightly increases with shear at higher temperatures. When CNTs are introduced, there is a large difference between the resistivity of the sheared and non-sheared nanocomposite. The sheared PNCs when the CNTs are aligned parallel to each other, have higher resistivity, which is possibly due to the higher concentration at which the percolation threshold occurs in this arrangement. The resistivity decreases overall, as the temperature increases from 0 to 50 °C. These results show that CNTs can be used to control and fine tune the desired macroscopic physical properties of nanocomposites, by concentration and orientation, such as electrical conductivity, for applications where such properties are necessary.

Papers in the Appendix were published in electronic format as Volume 1534

Oligo(ethylene glycol)-oligo(propylene glycol)-oligo(ethylene glycol) (OEG-OPG-OEG) triblock copolymers are hydrogel forming and extensively investigated in the field of drug release due to their biocompatibility and thermo-sensitivity. Here the synthesis and characterization of OEG-OPG-OEG based polymer networks from methacrylated oligomers by photo-irradiation are reported. Two precursors were selected to have comparable hydrophilicity (80 wt% OEG content) but different molecular weights of M n = 8400 g·mol-1 and 14600 g·mol-1. The precursor solutions were prepared in concentration 10 to 30 wt%. The resulting polymer networks prepared from high M n precursors exhibited higher swellability at equilibrium (up to 3400%) and mechanical properties in the range of G’ ∼ 0.1 to 1 kPa at 5 °C compared to networks based on low M n precursors. A more significant thermo-sensitive behavior in terms of swellability, volumetric contraction and mechanical transition, starting at 30 °C could also be observed for the networks based on high M n precursors, thus promoting future application in the field of drug release.

In the present work, we focus on δ-Gd6UO12 phase and its stability under reducing conditions. This later point is interesting regarding reducing environment that could exist in some nuclear storage sites and that could possibly degrade δ–compounds. A polycrystalline δ-Gd6UO12 sample was prepared by sintering cubic-Gd2O3 and UO2 mixed powders under an air atmosphere. The resulting pellets were then characterized and reduced by heat treatment under an Ar with H2 5% atmosphere. XRD analysis of the sample after reduction did not confirm the reduction into Gd6UO11 but a decomposition of the δ-compound. Preliminary characterizations of these decomposition products are presented.

Central to the idea of metamaterials is the concept of dynamic homogenization which seeks to define frequency dependent effective properties for Bloch wave propagation. Recent advances in the theory of dynamic homogenization have established the coupled form of the constitutive relation (Willis constitutive relation). This coupled form of the constitutive relation naturally emerges from ensemble averaging of the dynamic fields and automatically satisfies the dispersion relation in the case of periodic composites. Its importance is also notable due to its invariance under transformational acoustics. Here we discuss the explicit form of the effective dynamic constitutive equations. We elaborate upon the existence and emergence of coupling in the dynamic constitutive relation and further symmetries of the effective tensors.

In this work we report a specialized reactive force field (ReaxFF) developed for the study of alumina/epoxy interfaces. Force field parameters were obtained by fitting the reactions of small clusters and separate components of epoxies on alumina surfaces in the alpha phase. We also introduce a procedure to obtain crosslinked epoxies based on a proximity criterion to drive reactions and induce crosslinking. Properties of the resulting polymer, like the coefficient of thermal expansion, are found to be of the same order of magnitude as in experiments. Molecular dynamics was used to calculate the adhesion between these polymers and different alumina surfaces: Al2O3-deficient, Al-terminated, O-terminated, 12% and 75% hydroxylated. Typical values for strong adhesion are about 0.70 J/m2 which compare well with previously reported works. The role of defects is also studied.

It has been argued that for the simulation of amorphous materials, the larger the periodic supercell the better the representation. We contend that for certain properties there is a minimum supercell size above which one obtains a good representation of the topological and electronic collective properties of the material independent of the size. To show this contention we have chosen two periodic supercells of bismuth, one with 64 atoms and another with 216 atoms, which were amorphized using our undermelt-quench approach [1]. The originally crystalline structures were subjected to a heating-and-cooling process starting at an initial temperature of 300 K and linearly going up to 540 K, in 100 simulational steps, 4.5 K just below the melting temperature of bismuth (the undermelt section of the process) under normal conditions of pressure. Next, the sample was cooled down to 0K (the quench section of the process), in 225 simulational steps with the same absolute cooling rate as the heating process. Then the samples obtained were geometry-optimized to find the final metastable amorphous structures. These structures were analyzed by calculating their radial (pair) distribution functions, the plane angle distributions and the electron densities of states. Results will be presented that manifest that after proper normalization due to the difference in the number of atoms and the number of electron energy levels, the two structures are, for all practical purpose, the same, indicating that in this case, the size of the cell does not seem to play a major role in the properties determined.

Much has been reported on the excellent performance of the Eu2+ activated SrI2-scintillator in spectroscopic applications, like the high light yield (97 660 ph/MeV) and good energy resolution (2.7% FWHM at 662 keV). The exploitation of these properties for other application fields is limited by the hygroscopic nature of the SrI2. Single crystal scintillating screens exhibit high spatial resolution, this combined with the high density, high effective atomic number, and the high light yield of the SrI2 could be used for high resolution X-ray imaging.

Some of the questions we tried to answer in this work are the following: owing to the excellent performance of the SrI2-scintillator in spectroscopic applications, how would it perform in X-ray imaging applications. X-ray images are described based on their (spatial) resolution and contrast, how would they look like when recorded using the SrI2-scintillator detector.

First a packaging technique was developed that protected the hygroscopic screens during the measurements. Our results show a high resolution of the images obtained with thin SrI2-scintillator screens both in 2D radiography and 3D tomography measurements. With these results, we think that the SrI2-scinitillator is not only a candidate for spectroscopic applications, but also for high resolution X-ray imaging purposes.

Eutectic fibers consisting of an ordered arrangement of LiF fibrils inside a LiREF4 matrix (RE = Y, Gd) can be grown with the micro-pulling-down method at sufficiently large pulling rate exceeding 120 mm/h. The distance between individual fibrils could be scaled down to 1 µm at 300 mm/h pulling. LiF-LiYF4 has stronger tendency to form facetted eutectic colonies than LiF-LiGdF4, explained by the larger entropy of melting of the former.

We report on the direct synthesis of multi-layer boron nitride nanosheets (BNNSs) and their electron microscopic characterization. The synthesis process is carried out by irradiating hexagonal boron nitride (h-BN) target using short laser pulses. Scanning electron microscopy showed large area (≈50×50 μm2) flat layers of BNNSs transparent to the electron beam. Low magnification transmission electron microscope (TEM) is used to characterize different areas of nanosheets. TEM revealed that each individual nanosheet is composed of several layers. High resolution TEM (HRTEM) measurements confirmed the layered structure. HRTEM analysis of the edge of a nanosheet showed 10 layers from which we obtained the thickness (3.3nm) of an individual nanosheet. Selected area electron diffraction pattern indicated polycrystalline structure of nanosheets. Raman spectroscopy clearly identified E2g vibrational mode related to h-BN.

Polyurethanes are widely used, from medical devices to electrical materials to consumer goods. These materials have chemical stability issues which impact the mechanical stability. Infrared micro spectroscopy has been used to study polyurethane degradation, but due to experimental limitations, samples examined were no smaller than approximately 15 microns on a side. Because of the complex chemistry of urethanes, chemical examination of the material on a much higher spatial resolution scale would be valuable.

A relatively new technique, Attenuated Total Reflection Fourier Transform Infrared Spectrochemical MicroImaging has been used to examine degraded polyester urethanes. Rather than using a single-element detector, a two dimensional array detector generates thousands of spectra simultaneously. In addition, a germanium prism generates a magnification effect; resulting in a significantly higher spatial resolution. The net output of the analysis is a hypercube of high resolution infrared spectra showing urethane degradation progression on a much smaller spatial scale than was previously possible.

Nanostructuring has been the foremost approach to the manufacture of high-performance thermoelectric materials for nearly a decade. This study explores a novel nanostructuring technique, attrition-enhanced nanocomposite synthesis, in maximum indium-filled, iron-substituted cobalt antimonide skutterudites. In0.3Fe0.8Co3.2Sb12 was synthesized and subjected to varying degrees of mechanical attrition (via ball milling). These samples exhibited increased indium precipitation coincident with the duration of mechanical attrition. Indium readily diffused through the skutterudite crystal structure and rapidly precipitated forming 20-50 nm-sized indium-rich inclusions during sintering.

In this work, composites consisting of the Al 2024 matrix reinforced with β-Al3Mg2 particles have been produced by powder metallurgy with the aim of increasing the strength of the matrix and, at the same time, reducing the density of the material. The β-Al3Mg2 phase represents an ideal candidate as reinforcement in lightweight composites due to its low density and high-temperature strength. The β-Al3Mg2 reinforcement remarkably improves the mechanical properties of the 2024 matrix. In particular, the composite with 20 vol.% reinforcement display yield and compressive strengths exceeding that of the unreinforced matrix by about 120 and 180 MPa, while retaining appreciable plastic deformation of about 30 %. The strength of the material is further increased for the samples with 30 and 40 vol.% of β-Al3Mg2 phase, however, the composites show reduced plastic deformation of 11 and 4.5 %. Furthermore, the addition of the low-density β-Al3Mg2 particles decreases the density of the materials below that of the unreinforced 2024 matrix, considerably increasing the specific strength of the composites.

Microstructural variations of directionally-solidified (DS) MoSi2/Mo5Si3 eutectic composites caused by ternary additions of V, Cr, Nb, Ta and W were investigated. Ternary addition of relatively large amount of V resulted in the apparent modification of the morphology as well as the macroscopic inclination angle of one type of the interfaces extending nearly along the growth direction in the DS ingots. Ternary addition of Cr was found to change the microstructures of the DS ingots from a cellular-type with coarse boundary regions to a plate-like cellular-type with increasing the amount of the ternary addition. No significant change of scriptlamellar morphology was observed for the DS ingots containing Nb, Ta and W irrespective of the amount of the ternary addition.

The unrestrained combustion of fossil fuels has resulted in vast pollution at the local scale throughout the world, while contributing to global warming at a rate that seriously threatens the stability of many of the world's ecosystems. Solar photovoltaic (PV) technology is a clean, sustainable and renewable energy conversion technology that can help meet the energy demands of the world’s growing population. Although PV technology is mature with commercial modules obtaining over 20% conversion efficiency there remains considerable opportunities to improve performance. The nearly global access to the solar resource coupled to nanotechnology innovation-driven decreases in the costs of PV, provides a path for a renewable energy source to significantly reduce the adverse anthropogenic impacts of energy use by replacing fossil fuels. This study explores several approaches to improving indium gallium nitride-based PV efficiency with nanotechnology: optical enhancement, microstructural optimization for electronic material quality and increasing the spectral response via bandgap engineering. The results showing multibandgap engineering with InGaN and impediments to widespread deployment and commercialization are discussed including technical viability, intellectual property laws and licensing, material resource scarcities, and economics. Future work is outlined and conclusions are drawn to overcome these limitations and improve PV device performance using methods that can scale to the necessary terawatt level.