Effects of the amount of fillers and of the crosslink density on the mechanical behavior of carbon‐black filled styrene butadiene rubbers

Several carbon‐black filled styrene‐butadiene rubbers are subjected to monotonic uniaxial tension tests in order to investigate the effects of the amount of fillers and of the crosslink density on their mechanical properties. The Young modulus, the volume changes associated with material damage and the stretch to failure are extracted and discussed. Results compare well to the literature results when exist and quantitative analysis are proposed when possible. Results show that filled rubbers are not incompressible when submitted to uniaxial tension tests and their volume changes are strongly dependent of the amount of fillers but are unaffected by the crosslink density. The latter shows strong impact on the filled rubbers stretch to failure but more interestingly this impact is comparable to what is encountered in unfilled rubbers. The stretch to failure is improved by the addition of fillers with an optimum for material filled around 30 phr. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation of transparent PMMA/Fe(IO3)3 nanocomposite films from microemulsion polymerization

Polymethyl methacrylate (PMMA)/Fe(IO₃)₃ nanocomposite thin films are obtained by in situ particle generation in microemulsions and subsequent photopolymerization of a mixture containing methyl methacrylate, trimethylolpropane triacrylate, and crystallized iron iodate (Fe(IO₃)₃) nanorods. Hyper‐Rayleigh scattering measurements combined with X‐ray diffraction, transmission electron microscopy, and dynamic light scattering are first used to probe in situ the crystallization kinetics of iron iodate nanorods in water‐in‐oil microemulsions prepared with methyl methacrylate as the oil phase and marlophen NP12 as a surfactant. Trimethylolpropane triacrylate is then added as a crosslinker before spin‐coating. Films are deposited on glass substrates for the nonlinear optical characterizations and on silicon wafers for the piezoelectric and mechanical measurements. Nanocomposite films treated by corona discharge are finally characterized through optical microscopy, laser Doppler vibrometry, and Brillouin spectroscopy. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1203‐1211, 2013     

Topology optimization of periodic layouts of dielectric materials

A topology optimization method is used to design two dimensional periodic structures with desirable transmission properties by distributing two materials of different permittivity over a rectangular representative cell. A plane wave expansion of the electric field at the input and output boundaries is used in the analysis. This allows non-homogeneous material distributions near the boundaries. Numerical examples are used to verify the robustness of the method and to investigate the importance of retaining higher modes in the expansions. It is found that the optimization problem typically admits possibly many local optima and the relevance of higher modes depends on the nature of the solution found. In some instances, higher modes play an important role and using only the dominant mode in the analysis is shown to result in errors in the evaluation of the performance of the design.     

Investigation of the nitrogen-nickel-titanium system: The isothermal section at 900 °C

Phase relations in the ternary system N-Ni-Ti have been established experimentally for the 900 °C isothermal section assisted by thermodynamic modeling. Phase equilibria are characterized by an appreciable amount of up to ≅11 at. % N dissolved in the octahedral interstices of the crystal structure of Ti₂Ni. Two-phase equilibria are formed at 900 °C among the pairs Ti₂N + Ti₂NiN_x, TiN_1-x + Ti₂NiN_x, TiN_1-x + TiNi_1-x, and TiN_1-x + Ni(Ti)_x. The investigation is based on X-ray powder diffraction, metallography, scanning electron microscopy, and electron probe microanalysis techniques on about 50 alloys, which were prepared by arc melting or high-frequency levitation melting of appropriate blends of Ti,Ni-powders with TiN used to introduce nitrogen. Key experiments related to the N solubility in the Ti₂Ni phase have been triggered by an interactively performed thermodynamic modeling. The experimental results are in fine agreement with the thermodynamic calculation.     

Comparison of two models of a double inlet miniature pulse tube refrigerator: Part B electrical analogy

The design of a double inlet pulse tube refrigerator is investigated by means of an analogy with an electric circuit. The results obtained are compared with both those of the thermodynamic model (Part A) and experiments. The basic formulation of equivalent electronic components is discussed and a few improvements are proposed for adjusting the theoretical expressions of the electric impedance concerning the capillaries and the regenerator. Then additional effects such as pressure drops due to geometrical singularities are taken into account considering the different internal flow regimes that may occur. Besides a simplified formulation for the regenerator efficiency is deduced from considerations on its harmonic functioning. In this analysis, the emphasis concerns principally the design of miniature cryocoolers dedicated to electronic applications. Those models are applied to a commercial miniature refrigerator. A discussion of their relevance is achieved and a few suggestions on the refrigerator design are proposed in order to improve the cooling production.     

Nebulized Gadolinium‐Based Nanoparticles: A Theranostic Approach for Lung Tumor Imaging and Radiosensitization

Lung cancer is the most common and most fatal cancer worldwide. Thus, improving early diagnosis and therapy is necessary. Previously, gadolinium‐based ultra‐small rigid platforms (USRPs) were developed to serve as multimodal imaging probes and as radiosensitizing agents. In addition, it was demonstrated that USRPs can be detected in the lungs using ultrashort echo‐time magnetic resonance imaging (UTE‐MRI) and fluorescence imaging after intrapulmonary administration in healthy animals. The goal of the present study is to evaluate their theranostic properties in mice with bioluminescent orthotopic lung cancer, after intrapulmonary nebulization or conventional intravenous administration. It is found that lung tumors can be detected non‐invasively using fluorescence tomography or UTE‐MRI after nebulization of USRPs, and this is confirmed by histological analysis of the lung sections. The deposition of USRPs around the tumor nodules is sufficient to generate a radiosensitizing effect when the mice are subjected to a single dose of 10 Gy conventional radiation one day after inhalation (mean survival time of 112 days versus 77 days for irradiated mice without USRPs treatment). No apparent systemic toxicity or induction of inflammation is observed. These results demonstrate the theranostic properties of USRPs for the multimodal detection of lung tumors and improved radiotherapy after nebulization.     

Ultrasmall Nanoplatforms as Calcium‐Responsive Contrast Agents for Magnetic Resonance Imaging

The preparation of ultrasmall and rigid platforms (USRPs) that are covalently coupled to macrocycle‐based, calcium‐responsive/smart contrast agents (SCAs), and the initial in vitro and in vivo validation of the resulting nanosized probes (SCA‐USRPs) by means of magnetic resonance imaging (MRI) is reported. The synthetic procedure is robust, allowing preparation of the SCA‐USRPs on a multigram scale. The resulting platforms display the desired MRI activity—i.e., longitudinal relaxivity increases almost twice at 7 T magnetic field strength upon saturation with Ca²⁺. Cell viability is probed with the MTT assay using HEK‐293 cells, which show good tolerance for lower contrast agent concentrations over longer periods of time. On intravenous administration of SCA‐USRPs in living mice, MRI studies indicate their rapid accumulation in the renal pelvis and parenchyma. Importantly, the MRI signal increases in both kidney compartments when CaCl₂ is also administrated. Laser‐induced breakdown spectroscopy experiments confirm accumulation of SCA‐USRPs in the renal cortex. To the best of our knowledge, these are the first studies which demonstrate calcium‐sensitive MRI signal changes in vivo. Continuing contrast agent and MRI protocol optimizations should lead to wider application of these responsive probes and development of superior functional methods for monitoring calcium‐dependent physiological and pathological processes in a dynamic manner.     

Microstructure investigation and thermal stability of 99.1% aluminum processed by equal channel angular extrusion

Microstructure evolution of 99.1% aluminum after equal-channel angular extrusion (ECAE) and subsequent heat-treatment was investigated. After deformation the samples were annealed at different temperatures. The deformed and annealed states were characterized by Transmission Electron Microscopy (TEM), X-ray diffraction (XRD), and microhardness tests. It was shown that the observed microstructure changes during subsequent annealing have to be associated with recovery and cells formation. The initial stages of recovery were investigated using weak-beam technique. The microstructure obtained after annealing for 1 h at 100 °C consists of some arrangements of the dislocations into sub-grain boundaries within the wide preexisting grains. Annealing at 300 °C led to the appearance of a duplex microstructure consisting of bands of slightly coarsened grains associated with refined grains. No growth of dislocation cells was observed up to 400 °C. In XRD measurements, the lattice parameter increase with subsequent heating. This indicates a continuous grain growth during annealing. This is due to the important increase of coherency length, D observed parallel to a substantial decrease of rms-strain, ε.     

Modeling of steel and concrete strains between primary cracks for the prediction of cover-controlled cracking in RC-beams

After cracking, the intact concrete between two consecutive primary cracks remains elastic and the maximum concrete stress is less than the tensile strength of concrete. However, under increasing loading, cover-controlled cracks occur at the steel-concrete interface causing a loss of bond and hence a loss of tension stiffness. The cover-controlled cracks are internal concrete cracks that initiate at steel rib location and are contained within the concrete cover. In this paper, steel and concrete strain distribution between two consecutive primary cracks are modeled based on a linear assumed distribution of the bond stress at the steel-concrete interface. The accurate calculation of the tensile concrete strain allows introducing new criteria for cover-control cracking initiation based on a peak value of steel stress calculated at crack location.