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...     

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     

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.     

Oxygen Tracer Diffusion in Polycrystalline Calcium-Doped Lanthanum Chromites

Oxygen tracer diffusion in polycrystalline (La,Ca)CrO_3−delta was studied by the gas-solid isotope exchange reaction in combination with a depth-profiling technique using secondary-ion mass spectroscopy, which allowed determination of coefficients of lattice and grain-boundary diffusion separately. A significant contribution of fast grain-boundary diffusion was confirmed. The lattice diffusion coefficient increased with increased acceptor content and decreased oxygen partial pressure, which was consistent with the currently established point defect model and, thereby, suggested that the lattice oxide ions diffused by a vacancy mechanism.     

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.     

Piezoelectric polarization in the radiative centers of GaInN/GaN quantum wells and devices

We identify, quantify, and correlate the polarization dipole across the well of device-typical piezoelectric GaInN/GaN heterostructures with the luminescence properties of the well. This quantity reflects in the asymmetry of the barrier height on either side of the well. By a detailed comparison of photoreflection, electroreflection, low and high excitation density photoluminescence we find that a very similar splitting occurs in the emission characteristics of the well. We therefore conclude that the electronic band structure within the wells is also to a very large extent controlled by the quantity of the polarization dipole in such polarization heterostructures.     

Effect of substrate on gradient domain morphology formed in acrylate copolymer/fluoro-copolymer blends

The effect of the substrate on the gradient domain morphology was investigated for immiscible blends of poly(2-ethylhexyl acrylate-co-acrylicacid-co-vinylacetate) [P(2EHA-AA-VAc)] and poly(vinylidene fluoride-co-hexafluoro acetone) [P(VDF-HFA)]. The blends were prepared on substrates of poly(dimethyl siloxane) (PDMS) coated on a liner and of poly(tetrafluoro ethylene) (PTFE) from a THF solution by coating. The chemical compositions and the cross-sectional morphology of the surface (surface in contact with air) and bottom (surface in contact with substrate) sides were examined by attenuated total reflection Fourier transform infrared spectroscopy and scanning electron microscopy. The P(2EHA-AA-VAc)/P(VDF-HFA) (50/50), (30/70) blends prepared on PDMS revealed a gradient domain morphology, whereas the (50/50) and (30/70) blends prepared on PTFE formed a sea-island type of phase separation structure. On the other hand, when the P(2EHA-AA-VAc)/P(VDF-HFA) (70/30) blend was prepared on PTFE, P(2EHA-AA-VAc) and P(VDF-HFA) components segregated at the surface and the bottom, respectively. We concluded that the affinity between P(VDF-HFA) and the substrates strongly influenced the formation of the gradient domain morphology and the surface segregation of P(2EHA-AA-VAc).     

Alcohol electrooxidation at Pt and Pt–Ru sputtered electrodes under elevated temperature and pressurized conditions

The electrooxidation properties of methanol and 2-propanol, which are both promising candidates for direct alcohol fuel cells (DAFCs), have been studied under elevated temperature and pressurized conditions. Sputter-deposited Pt and Pt–Ru electrodes were well-characterized and utilized for the electrochemical measurement of the alcohol oxidation at 25–100 °C. The Pt electrode prepared at 600 °C had a flat surface, and the Pt–Ru formed an alloy. The electrochemical measurements were carried out in a gas-tight cell under elevated temperature, which accompanies the pressurized condition. This is a representative example of the DAFC rising temperature operation. As a result, at 25 °C, the onset potential of the 2-propanol oxidation is about 400 mV more negative than that of the methanol oxidation, and current density of the 2-propanol oxidation exceeds that of the methanol oxidation. Conversely, at 100 °C, the methanol oxidation current density overcomes that of 2-propanol, and the onset potentials of the two are almost the same. The highest current density for the methanol oxidation is obtained at the Pt:Ru = 50:50 electrode, whereas at the Pt:Ru = 35:65 for the 2-propanol oxidation. A Tafel plot analysis was employed to investigate the reaction mechanism. For the methanol oxidation, the number of electrons transferred during the rate-determining process is estimated to be 1 at 25 °C and 2 at 100 °C. This suggests that the methanol reaction mechanism differs at 25 and 100 °C. In contrast, the rate-determining process of the 2-propanol oxidation at 25 and 100 °C was expected to be 1-electron transfer which accompanies the proton-elimination reaction to produce acetone. Consequently, it is deduced that methanol and 2-propanol have an advantage under the rising temperature and room temperature operation, respectively.