Colloidal Consolidation of Ceramic Nanoparticles by Pressure Filtration

The applied pressure and suspension height during consolidation of an aqueous suspension of nanometer-sized particles (24 nm hydroxyapatite, 30 nm SiC, 68 nm 8 mol% yttria-stabilized zirconia, 150 nm Al₂O₃, and 800 nm SiC) were continuously recorded using a pressure filtration apparatus. The packing density decreased when the particle size was less than 70 nm. The final packing density of 150−800 nm particles at 19 MPa was strongly influenced by the surface charge. However, surface charge does not affect the packing density of particles less than 70 nm. The ratio of the energy applied to two particles during consolidation to the interaction energy between two particles in a suspension was correlated to the packing density. The low packing density of 20−30 nm particles was improved by steric stabilization. The estimated thickness of the dispersant layer adsorbed on the particle surfaces was less than 1 nm and nearly independent of the molecular weight of the dispersants. When the applied pressure was released, the height of the consolidated cake increased because of the release of the elastic strain stored in the dispersant layer.     

Synthesis of active sites for alkene metathesis reaction on molybdenum oxide films by the reaction with alkylidene radicals

A super active catalyst (T.F. = 0.2 0.3) for alkene metathesis reaction was prepared by coordinating CH₂ radicals onto sublimed molybdenum oxide films, where the radicals were prepared by the reaction of CH₂I₂ with Al or Mg metals deposited near the oxide film.The authors are indebted to the Iwatani Naoji Foundation and the Murata Science Foundation for the support of this work.     

Selective hydrolysis of polyunsaturated fatty acid-containing oil withGeotrichum candidum lipase

Polyunsaturated fatty acids (PUFA), especially docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), can be concentrated in glycerides by hydrolyzing tuna oil withGeotrichum candidum lipase, the main components in the resulting oil being triglycerides. The reaction mechanism of this selective hydrolysis was investigated. Although the lipase acted well on the esters of oleic, linoleic, and α-linolenic acids, it did not affect the esters of γ-linolenic acid, arachidonic acid, EPA, and DHA as much. The action of PUFA-glycerides was mono-> di- > triglycerides. Furthermore, the condensation of PUFA-partial glycerides and PUFA occurred even in the presence of a large amount of water, and the partial glycerides converted to the triglycerides by transacylation. These results suggested that the PUFA-rich triglycerides were accumulated in the glyceride fraction by the following mechanism: The PUFA-partial glycerides generated by the hydrolysis were converted to PUFA-triglycerides by condensation and transacylation reactions. As the PUFA-triglycerides formed were the poor substrates of lipase, they were accumulated in the reaction mixture.     

Direct Evidence of Dopant-Enhanced Grain-Boundary Sliding in Yttria-Stabilized Zirconia Bicrystals

Compression tests were conducted at 1400°C in air for undoped and Si-doped yttria-stabilized zirconia (YSZ) bicrystals with the same orientation relationship (Σ=5, [001]/{210} grain boundary). It was found that the macroscopic grain-boundary slidings are observed during the deformation in both undoped and doped bicrystals, and the sliding displacements increase almost linearly with increasing total displacements. It is distinctly demonstrated that the Si-doped bicrystal exhibits a sliding displacement that is a few times larger than the undoped bicrystal. In addition, the total strain of the Si-doped bicrystal at a failure is much larger than that of the undoped bicrystal. It can be stated that Si doping in YSZ not only enhances the grain-boundary sliding but also suppresses its failure.     

Cellulose graft copolymers. III. Effects of oxygen on graft copolymerization of ethyl acrylate with γ-irradiated cellulose

The effects of oxygen on graft copolymerization of ethyl acrylate from methanol–water systems with γ-irradiated fibrous cotton cellulose were investigated by electron spin resonance spectroscopy and by the formation of cellulose–poly(ethyl acrylate) copolymer. The concentrations of free radicals in cellulose irradiated dry in an atmosphere of nitrogen at 25°C decreased during postirradiation storage in nitrogen or oxygen. The concentration of free radicals in the irradiated cellulose, moisture regain of the irradiated cellulose, and formation of cellulose–poly(ethyl acrylate) copolymer decreased with increase in temperature and time of postirradiation storage and to a greater extent when stored in oxygen rather than in nitrogen. From the decrease in moisture regain of irradiated cellulose during postirradiation storage, it was concluded that increased intermolecular bonding occurred in irradiated cellulose during storage in both nitrogen and oxygen atmospheres. When irradiated celluloses which had been stored in either oxygen or nitrogen were copolymerized with ethyl acrylate at 60°C, less formation of copolymer was observed than when the copolymerization reactions were conducted at 25°C. It was concluded that there was no evidence for the formation or decomposition of cellulose peroxides during these reactions and that formation of graft copolymer depended primarily on the concentration of free radicals in the irradiated cellulose at the time of copolymerization.     

Graft frequency of graft copolymers by chain transfer of growing polymer radicals to trunk polymers containing nitro groups

The relationship between the chain transfer constant, extent of monomer conversion, and number of branches was derived for the graft copolymerization through chain transfer of growing polymer radicals to the pendent aromatic nitro groups on the trunk polymer. The equation derived enables us to predict the number of branches for a given monomer trunk polymer. The relationship obtained is compared with the experimental data previously reported for the graft copolymerization of styrene onto poly(vinyl p-nitrobenzoate). The value of α′, the ratio of nitro groups with branches to those which are attacked by polystyrene radicals, is less than unity except for the graft copolymers obtained with high initiator concentrations and at early stages of the reaction. This lowering of α′ is attributed to the steric hindrance of branches already formed on the trunk polymer which prevents the attack of polystyrene radicals on the nitro groups and side reactions, such as reaction of the nitroso groups formed as an intermediate with styrene.     

Phase transition and the packing structure of the side mesogenic groups of liquid crystalline side-chain copolymers

Summary Copolymers consisting of cholesteryl 11-methacryloyloxy-undecanoate (ChMO-10) and t-buthyl methacrylate (t-BMA) were studied by DSC method and by small angle X-ray scattering method (SAXS). Although homopolymer (pChMO-10) has two different packing structures which are a single-layer packing structure and a two-layer packing one, copolymers (co-pChMO-10-t-BMA) have only the single layer packing one in their mesophase. Furthermore, transition entropy at a clearing point of co-pChMO-10-t-BMA (80/20) is larger than that of pChMO-10. Adequate distance of the mesogenic groups in the direction of a short axis of the mesogenic groups, produced by introduction of non-mesogenic units, seems to stabilize the single-layer packing structure.     

Thermal conductivity of homogeneous alignment networks formed with mono‐ and bi‐functional polymerizable liquid crystals

Mixtures consisting of mono‐functional polymerizable liquid crystals (PLC) having a polymerizable moiety on the molecular short axis terminal and a bi‐functional PLC having the polymerizable moieties on the molecular long axis terminals were prepared. These mixtures had a wide liquid crystal range. Uniaxially aligned films were prepared from the PLC mixtures by photo polymerization after aligning the molecular directions by the rubbing method. The thermal conductivity of the films increased from 0.45 to 0.68 W/m · K with the increase ofthe content of the bi‐functional PLC. The relation between the thermal conductivity and the PLC network styles was investigated from the aspect of the molecular order. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Instrumented charpy impact test of epoxy resin filled with irregular-shaped silica particles

The effect of particle size on the impact properties of an epoxy resin has been studied. This resin was filled with irregular-shaped silica particles prepared by crushing fused natural raw quartz. These particles were sorted into six groups of different mean sizes ranging from 2 to 47 μm. The impact properties were measured by an instrumented Charpy type impact tested, which can record a load-displacement curve during impact fracture. The impact absorbed energy (U) was measured using specimens having a U-shaped blunt notch, and the impact fracture toughness (K_CI) was measured using specimens having a sharp crack introduced by a fresh razor blade. As the particle size decreased. U increased and K_CI decreased. The fractured surfaces and crack tip regions were observed using a scanning electron microscope to clarify the above phenomena.