Micromechanical Characterization of Electrophoretic-Deposited Green Films

Low-load indentation experiments have been performed on electrophoretic-deposited films of SiC particles on a graphite substrate. Films with thicknesses between 60 and 300 µm prepared at two current intensities and subsequently dried under different humidities were indented with spherical indenters with nominal radii of 10, 50, and 150 µm. Force-displacement data were analyzed to determine contact pressure and elastic modulus versus depth results. The modulus and contact pressure behavior with depth exhibited opposite trends with indenter radius: the modulus increase was least for the 10 µm and greatest for the 150 µm, whereas the contact pressure was the inverse. The results may be rationalized by plotting modulus normalized to the ratio "contact radius/film thickness" ( a / t ), whereas the contact pressure results at small a / t could be normalized when plotted versus contact strain, i.e., contact radius divided by indenter radius ( a / R ). These approaches enabled the properties of the variously deposited films to be compared. Additional interesting microstructural and cracking behavior patterns are also reported.     

Emulsifier‐free emulsion polymerization of acrylonitrile: Effect of in situ developed Cu(II)/glycine chelate complex initiated by monopersulfate

The catalytic effect of various Cu(II) salts and Cu(II) chelate complexes of certain amino acids on the emulsion polymerization of acrylonitrile in the absence of added emulsifier was investigated in experiments. The CuSO₄/glycine chelate complex was chosen for a detailed kinetic study of acrylonitrile polymerization. The polymerization was studied at varying concentrations of initiator, monomer, Cu(II), glycine, solvents, and TiO₂ over a temperature range of 30–60°C. The overall activation energy and the viscosity average molecular weight of the polymer were computed. From the kinetic and spectrophotometric studies, the mechanism of KHSO₅ decomposition by the Cu(II)/glycine complex and initiation of polymerization was suggested. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2785–2790, 1999     

Electroanalytical performance of nitrogen-containing tetrahedral amorphous carbon thin-film electrodes

Tetrahedral amorphous carbon (ta-C) consists of a mixture of sp(3)- and sp(2)-bonded carbon ranging from 60 to 40% (sp(3)/sp(3)+sp(2)) depending on the deposition conditions. The physical, chemical, and electrochemical properties depend on the sp(2)/sp(3) bonding ratio as well as the presence of incorporated impurities, such as hydrogen or nitrogen. The ability to grow ta-C at lower temperatures (25-100 °C) on a wider variety of substrates as compared to CVD diamond is an advantage of this material. Herein, we report on the structural and electrochemical properties of nitrogen-incorporated ta-C thin films (ta-C:N). The incorporation of nitrogen into the films decreases the electrical resistivity from 613 ± 60 (0 sccm N(2)) to 1.10 ± 0.07 Ω-cm (50 sccm N(2)), presumably by increasing the sp(2)-bonded carbon content and the connectedness of these domains. Similar to boron-doped diamond, these materials are characterized by a low background voltammetric current, a wide working potential window (~ 3 V), and relatively rapid electron-transfer kinetics for aqueous redox systems, including Fe(CN)(6)(-3/-4) and Ru(NH(3))(6)(+3/+2), without conventional pretreatment. Additionally, there is weak molecular adsorption of polar molecules (methylene blue) on the ta-C surface. Overall, the properties of the ta-C and ta-C:N electrodes are such that they could be excellent new choices for electroanalytical measurements.     

Oxygen Barrier of Multiwalled Carbon Nanotube/Polymethyl Methacrylate Nanocomposites Prepared by in situ Method

Multiwalled carbon nanotubes (MWCNTs)/poly(methyl methacrylate) (PMMA) nanocomposites were prepared by ultrasonic assisted emulsifier free emulsion polymerization technique with variable concentration of functionalized carbon nanotubes. MWCNTs were functionalized with H 2 SO 4 and HNO 3 with continuing sonication and polished by H 2 O 2 . The appearance of Fourier transform infrared absorption bands in the PMMA/MWCNT nanocomposites showed that the functionalized MWCNT interacted chemically with PMMA macromolecules. The surface morphology of functionalized MWCNT and PMMA/MWCNT nanocomposites were studied by scanning electron microscopy. The dispersion of MWCNT in PMMA matrix was evidenced by high resolution transmission electron microscopy. The oxygen permeability of PMMA/MWCNT nanocomposites gradually decreased with increasing MWCNT concentrations.     

Recent progress on cooled avalanche photodiodes for single photon detection

Abstract

Recent results on the properties of cooled avalanche photodiodes for single photon detection are presented. Results from Hamamatsu silicon photodiodes, originally developed as radiation-hard photodetectors for high energy physics experiments, are extremely encouraging. Gains of approximately 10,000 can be achieved with the APD operating in proportional mode. Together with a low noise amplifier they allow photon counting with extremely high efficiency and very low noise making cold APDs almost ideal single photon detectors. Operation of APDs in Geiger mode is also reported, together with measurements of detection efficiency and noise as function of operating voltage. Prospects and hopes for future work are briefly summarized.     

Effect of Laser Linewidths on Nonlinear Optical Processes Exploiting Electromagnetically Induced Transparency

Abstract

We investigate the effects of laser linewidths on the efficiency of sum-frequency generation when electromagnetically induced transparency is exploited in the manner suggested by Harris and his co-workers, which makes use of pump lasers and an intense coupling laser. The linewidths are assumed to be due to phase diffusion. Analytic expressions are obtained which are an excellent approximation when the coupling laser is strong. It is found that increasing the coupling-laser linewidth strongly increases the opacity of the medium; a first consideration is therefore to minimize this linewidth. The relative efficiency of sum-frequency generation is measured by the ratio R of the absolute value of the third-order susceptibility, χ₃, to the imaginary part of the first order susceptibility, χ₁. For large intensities of the coupling field, we show that |χ₃| is independent of the laser linewidths, whereas it increases the value of Im(χ₁).     

Influence of the plasma profile and the antenna geometry on the matching and current distribution control of the ITER ICRF antenna array. Optimization of the decoupling-matching system

The eight triplets of straps of the ITER ICRF antenna array are fed through 8 matching circuits and 4 hybrids to ensure load resilience. Decouplers are used to mitigate the effects of triplet mutual coupling. They also control the array phasing. The electrical constraints on the decouplers for different layouts with heating (H) or current drive (CD) phasing are compared starting from the TOPICA matrix computed for the last antenna plug design and the reference (most pessimistic) plasma profile “2010low” provided by IO. It is shown that this last profile provides a significant decrease of plasma coupling and increase of mutual coupling with respect to the previous reference profile “Sc2short17”. This results in a larger range of decoupler reactance X_dec and voltage V_Xdec needed. This range can be reduced when using 10 decouplers instead of the 7 needed for the same forward power P_Gk+ of the 4 power sources. For H phasing only 4 decouplers could be used but with different P_Gk+ (P_Gk+ ratio up to 1.5–2.5). For CD phasing and same plasma profile the power capability P_tot is increased by 25% with a decoupler layout allowing much smaller poloidal phasing than the 90° provided by the hybrids. A decrease of the distance antenna-plasma profile reduces the normalized decoupler voltage V_Xdec/√P_tot with no significant change of the X_dec range. The recess of the vertical septa between the strap boxes increases the plasma coupling but has the drawback of also increasing the mutual coupling between triplets: the needed range of X_dec and of V_Xdec/√P_tot is increased in proportion.     

Ultrasound aided extrusion process for preparation of polyolefin–clay nanocomposites

A continuous ultrasound assisted process using a single screw compounding extruder with an ultrasonic attachment was developed to prepare polyolefin/clay nanocomposites. High‐density polyethylene and isotactic polypropylene were compared. The feed rate that controls the residence time of the polymer in the ultrasonic treatment zone was varied. Die pressure and power consumption were measured. Rheological properties, morphology, and mechanical properties of the untreated and ultrasonically treated nanocomposites were studied. Similarities and differences of obtained nanocomposites are discussed based on their properties and structural characteristics. The modified Halpin‐Tsai theory of composite materials has been employed in order to predict the effect of incomplete exfoliation of clay platelets on the Young's modulus of the nanocomposites. A good agreement between experimental and theoretical data has been observed when reduction of the reinforcement efficiency of clay had been incorporated through the reduced aspect ratio of elementary clay platelets. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Study of oxygen permeability and flame retardancy properties of biodegradable polymethylmethacrylate/starch composites

Polymethylmethacrylate/starch (PMMA/starch) composites were prepared by emulsion polymerization method using potassium persulphate (KPS) as the radical initiator. The interaction of starch with polymethylmethacrylate was evidenced by ultraviolet–visible (UV–visible) spectroscopy and Fourier transform infrared (FTIR) spectroscopy. The structure of PMMA/starch composite was studied by X‐ray diffraction (XRD) study and Scanning Electron Microscopy (SEM). The thermal properties of starch, PMMA/starch composites were compared with the virgin PMMA sample. The PMMA/starch composites were found to be flame retardant material from the measurement of limiting oxygen index (LOI) of samples. The biodegradability of the PMMA/starch composites were studied by active sludge water and it was found that degradability of composites increases with increasing time interval. The oxygen permeability of PMMA/starch composites was substantially decreased as compared to virgin PMMA. The reduction of oxygen permeability of the PMMA/starch composites may enable the materials applicable in packaging industries. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers