A polydimethylsiloxane diaphragm integrated with a sputtered thin film NdFeB magnet

Microsystem Technologies - In this paper we propose a MEMS fabrication process that enables a polydimethylsiloxane (PDMS) diaphragm to be integrated with a sputtered thin film permanent magnet...     

Three-dimensional reconstruction from serial section images by computer graphics

A method is described that allows a three-dimensional object to be reconstructed from micrographs of serial sections by means of computer graphics. The reconstructed object, which can be rotated three-dimensionally, is displayed on a colour visual display unit, and the object is shaded in order to provide an illusion of a three-dimensional structure. Moreover, the technique makes it possible to observe an inner structure as seen through an outer one.     

Effect of large dosage irradiation in vacuo on polyethylene

The effect of large dosage irradiation in vacuo on polyethylene was investigated by the method of double irradiation. Polyethylene was first irradiated with γ-rays to a dosage of several hundred Mrad in vacuo at 298°K. The formed radicals were destoryed, and the polymer, changed chemically and morphologically, was irradiated again in vacuo at 77°K with a dose of 12.7 Mrad. The thermal decay of radicals produced in polyethylene by the second irradiation was investigated. The results show that many double bonds are formed in the sample irradiated to several hundred Mrad on the first irradiation. Alkyl radicals produced by the second irradiation react with these double bonds yielded by the first irradiation to form a large number of allyl radicals. These allyl radicals are much more stable than alkyl radicals radicals in vacuo at 298°K. In a sample not exposed to the first irradiation, almost all radicals formed by the second irradiation decay to form stable products. Crosslinks formed by a large amount of irradiation make the polyethylene matrix more rigid. This rigidity slows down the radical decay. These results suggest that the rate of radical accumulation in polyethylene irradiated in vacuo increases as the dosage increases.     

Effect of large dosage irradiation in air on polyethylene

The large dosage irradiation effect on polyethylene in air was examined by the method of double irradition. Polyethylene was first irradiated with γ-rays to a dosage of a few hundred Mrad in air at 298°K. The formed radicals were destroyed, and the polymer, changed chemically and morphologically, was irradiated again in vacuo at 77°K with a dose of 12.7 Mrad. The thermal decay of radicals produced in polyethylene by the second irrdiation was investigated. The results were compared with the sample not exposed to the first irradiation. The results were also compared with previous data of polyethylene irradiated in vacuo to a great extent and then treated in the same manner as that in the present experiment. The results show that scission of the polymer chain by oxidation makes the radical decay faster. Simultaneously, crosslinks formed in polyethylene irradiated in air to a great extent slow down the radical decay. Almost the same number of double bonds was formed in polyethylene irradiated in air as in polyethylene irradiated in vacuo. These double bonds react with alkyl radicals to form allyl radicals.     

Double helix of Agrobacterium tumefaciens succinoglycan in dilute solution

Succinoglycan samples ranging in weight-average molecular weight from 1.4×10⁵ to 10.5×10⁵ (in 0.1 M aqueous NaCl at 25°C), prepared from native succinoglycan by sonication, were investigated by static light scattering and viscometory in 0.1 M aqueous NaCl. It is well known that the conformation of the polysaccharide changes at around 65°C. In order to confirm the conformation of the polysaccharide, the property of the polysaccharide in dilute solution was studied at both 25 and 75°C. The molecular weight of a sample at 25°C is the double of the value at 75°C. The molecular weight dependence of 〈s²〉_Z and [η] for succinoglycan shows that the polysaccharide is a rod-like polymer at 25°C and behaves like a semi-flexible polymer at 75°C in 0.1 M aqueous NaCl. Moreover, the linear mass density of the polysaccharide was almost twice that expected for single succinoglycan molecules. These results indicate that the conformation of the polysaccharide would be a double helix at 25°C and the helix melts to a single strand behaving as a semi-flexible chain above 65°C.     

Formation of chlorine species over magnesium oxide in the oxidative coupling of methane in the presence of carbon tetrachloride

The oxidative coupling of methane on magnesium oxide (MgO) has been studied in the presence of carbon tetrachloride (TCM) as a gas-phase additive. Addition of a small amount of TCM to the reactant stream improves the selectivity to C₂H₄, while the conversion of methane is not influenced by the additive. X-ray photoelectron spectra of the used MgO reveal the formation of chlorine species on the catalyst surface in quantities up to 0.20 of Cl/Mg (atomic ratio), although X-ray diffraction spectra of the catalyst show MgO only and the content of the chlorine species in the bulk phase estimated by X-ray fluorescence analysis is very low. It is concluded that the enhancement of the selectivity to C₂H₄ primarily results from the presence of surface chlorine species. The chlorinated species on the catalyst has been identified as MgCl₂.     

Convenient method for removing and concentrating hydrophobic organic compounds from water with amphiphilic polymers

A stable fluoroacrylate copolymer emulsion was successfully prepared by miniemulsion polymerization with fluoroacrylate, lauryl methylacrylate, and methyl methacrylate as monomers. Extremely hydrophobic fluoroacrylate, instead of conventional cosurfactants, was used as a reactive cosurfactant to stabilize the miniemulsions. The results indicated that fluoroacrylate retarded Ostwald ripening and allowed the production of stable miniemulsions. The chemical compositions of the copolymer were studied with Fourier transform infrared and ¹H‐NMR. The average composition of the copolymers prepared with miniemulsions was in good agreement with the feed ratio according to ¹H‐NMR from the integration ratios corresponding to typical protons of the individual monomers. The particle size distribution and morphology of the latex particles were determined with laser particle analysis and transmission electron microscopy. The particle size of the latex underwent no change in the process of miniemulsion polymerization, but the particle size distributions were broader than those of conventional emulsion polymerization. The effects of various reaction parameters, including the temperature and concentrations of the emulsifier and initiator, on the miniemulsion polymerization were also investigated, and the polymerization rate and conversion increased with increasing concentrations of nonylphenol polyethoxylate (with an average of 40 ethylene oxide units per molecule), cetyltrimethylammonium, and 2,2′‐azobisisobutyronitrile. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 641–647, 2007     

Inference of plastic deformation in weldment with parallel cracks from infrared thermography

Tensile tests are carried out by using the welded plate with two parallel cracks. The effects of the residual stress, the hardened zone by welding and the interaction between cracks on the plastic deformation near cracks and the crack opening displacement are examined by the experiment as well as the elasto plastic finite element analysis. A new technique for evaluating nondestructively the plastic deformation near cracks by using the infrared thermography is proposed. The heated region and the temperature rise measured by the thermography are compared with the plastic zone and the work of plastic deformation obtained by the analysis. The validity and the limitations of the application of the infrared thermography to the evaluation of the plastic deformation are discussed.     

Computational characterization on mechanical behavior of polymer electrolyte membrane based on nonaffine molecular chain network model

This paper investigates the mechanical behavior of polymer electrolyte membrane based on a nonaffine molecular chain network model (nonaffine model), which may account for the change in the entanglement situation for the physical linkages of the molecular chain during the deformation process. After the identification of the parameters used in the nonaffine model with the experimental data of the fresh membrane, a computational model is proposed for the degraded membrane, in which the swelling parts of the degraded membrane are replaced with voids. Employing the extended 2D homogenization method, the effect of the change in the entanglement situation for the physical linkages of the molecular chain and that of the macroscopic loading conditions on the mechanical behavior of the membrane with different volume fractions of voids are discussed. The results indicate that the dramatic increase in the average number of segments in a single chain, which occurs inside the microscopic sharp shear band, leads to a great strain softening after the macroscopic yield. Moreover, such strain softening tends to appear at early deformation stage for the membrane with high volume fraction of voids under high macroscopic triaxiality loading condition.