Melt-spinning and the thermal decomposition of mixed polymers containing polysilsesquioxane and polycarbosilane

Journal of Materials Science - We attempted melt-spinning and investigated the compatibility and thermal decomposition of a mixture comprising polysilsesquioxane and polycarbosilane for the purpose...     

Regime shifts observed in Lake Kasumigaura,a large shallow lake in Japan: Analysis of a 40‐year limnological record

Lake Kasumigaura, which is composed of the two basins (Nishiura and Kitaura), is a large, shallow, hypereutrophic lake. Phytoplankton and water quality records from the past forty years were analysed to elucidate whether or not, when, and what type of certain regime shifts may have occurred, based on using inferential regime shift detectors. Characteristics of the phytoplankton and water quality changes were similar at 6 sampling sites in the two basins, with 20 water quality parameters being classified into four groups, based on cluster analysis. Shifts in dominant plankton groups (DPGs) and water quality occurring almost concomitantly, concentration on the period from 1987 to 1992 (Shift A) and from 1997 to 2001 (Shift B), with those observed for the two basins usually being similar with small differences. Two types of inferential regime shift detectors (sequential t‐test type; Rodionov's RSD and sequential F‐test type: package strucchange in R) yielded similar timings and significances of the shifts. Furthermore, changes in skewness and conditional heteroskedasticity (package early warnings in R) usually represented early warning signals before the shifts. Correlation analysis and ratios of dissolved inorganic nitrogen (DIN) vs. total phosphorus (TP) supported the hypothesis that phosphorus was the phytoplankton biomass limiting nutrient, except for one period for the Nishiura basin. Neither the nitrogen:phosphorus (N/P) ratio hypothesis and ammonia–nitrate (NH₄‐N/NO₃‐N) hypothesis satisfactorily explain the DPGs before and after Shift A (Microcystis spp. and Planktothrix spp., respectively), although it may be possible that these ratios triggered the DPG change in this shift. A considerable increase in silicon was observed for Shift B when the DPGs changed from cyanobacteria to diatoms. Further studies on the accurate types and triggers of the regime shifts are necessary to better understand the interactions between ecosystem and water quality for this and similar lakes elsewhere.     

Enantiomeric Separation and Detection of 2-Arylpropionic Acids Derivatized with [(N,N-Dimethylamino)sulfonyl]benzofurazan Reagents on a Modified Cellulose Stationary Phase by High-Performance Liquid Chromatography

(RS)-2-Arylpropionic acids (2-APAs) were derivatized with the fluorogenic reagents, 4-[(N,N-dimethylamino)sulfonyl]-7-piperazino-2,1,3-benzoxadiazole (DBD-PZ) and 4-[[(N-hydrazinoformyl)methyl]-N-methyl]amino-7-[N,N-(dimethylamino)sulfonyl]-2,1,3-benzoxadiazole (DBD-COHz), and their enantiomeric separation by a chiral stationary phase high-performance liquid chromatography was investigated in the reversed-phase mode with H(2)O/CH(3)CN or H(2)O/MeOH as the mobile phase on a column of cellulose tris(3,5-dimethylphenyl carbamate) coated on a silica gel support (Chiralcel OD-R). The derivatives with DBD-PZ were enantiomerically separated well under the elution condition of H(2)O/MeOH, based on the π-π interaction between the derivatives and the stationary phase. The rigid and bulky structure of DBD-PZ was demonstrated to be more effective as compared to the less rigid ones. The derivatives with DBD-COHz were more efficiently separated into each enantiomer with H(2)O/CH(3)CN as the eluent. The effective separation was based on hydrogen-bonding interaction between the acid hydrazide of the derivatives and the carbamoyl moiety of the stationary phase. There was a reversal in the elution order of the enantiomers between the two fluorescent derivatives. The detection limits obtained for each enantiomer were approximately 10-30 fmol on column. The derivatization with the reagent and the concomitant use of the reversed-phase and chiral stationary-phase HPLC were demonstrated to be useful for the enantiomeric quantification in rat plasma after intravenous administration of flurbiprofen racemate, a representative of 2-APAs.     

Exfoliation of non-swelling muscovite on dodecylammonium chloride intercalation between layers using wet-jet milling

The exfoliation of layered muscovite with non-swelling property has been performed by combining various processes, such as heating, intercalation, and wet-jet milling. The c axis of muscovite was expanded from 2004.0 to 2022.8 pm at 800 °C without the destruction of crystallinity of muscovite. The heating at 800 °C led to the weak attraction force between potassium ions and silicate layers by hydroxylation of muscovite. The muscovite heated at 800 °C progressed the intercalation of dodecylammonium chloride (DDAC) into the layers effectively. Furthermore, the DDAC molecules were inserted to the interlayer of muscovite effectively by suppressing the formation of micelle of DDAC. The sedimentation test of wet-jet milled muscovite slurry showed that the relative packing density of muscovite was decreasing with increasing the amount of the intercalated DDAC. As results, the aspect ratio of muscovite prepared with combining the heating, the intercalation and the wet-jet milling was increased by 253% as compared to the raw muscovite. The aspect ratio was calculated from laser particle size distribution and thickness size distribution which was estimated from field emission-scanning electron microscopic images. The expansion of the interlayer led to the effective exfoliation of muscovite with high aspect ratio.     

Fiber template approach toward preparing one-dimensional silica nanostructure with rough surface

Silica nanofibers were grown on the surface of chitosan nanofibers used as templates by coating the surface with silica derived from the hydrolysis and condensation of tetraethoxysilane using ammonium hydroxide as a catalyst. This was followed by the decomposition of the chitosan template. The relationship between different processing factors (type of templates as well as amounts of catalyst and template) and the formation of silica nanofibers was examined. Varying the processing factors was found to be effective in controlling the morphology of the silica nanofibers. The use of chitosan nanofibers effectively led to the formation of one-dimensional silica nanofibers as the positively charged chitosan nanofibers promoted the deposition of the negatively charged silica nanoparticles through electrostatic attractive forces. Therefore, the chitosan nanofibers acted as good deposition sites for interacting with silica nanoparticles. Although a large amount of catalyst promoted the sol-gel reaction, the silica nanoparticles grew excessively in the solvent. Therefore, the surface structure of the prepared silica nanofibers could be controlled by varying the amount of chitosan template as this also varied the formation mechanism of the silica nanofibers. The resultant samples had a rough silica wall composed of densely assembled silica nanoparticles, with a high specific surface area (338 m²/g).     

Obui-himo syndrome

Normal variants of the venous system are relatively common and rarely cause severe symptoms. We report the case of a 5-month-old baby who displayed cyanotic color and swelling of arms whenever she was carried on the mother's back with a special band "Obui-himo". It was demonstrated by venography that the symptoms were caused by the absence of a cephalic vein and compression of axillary veins with the Obui-himo. In any country with a custom similar to the Obui-himo, these symptoms, if clinically encountered, are an indication that venography should be performed.     

Thermal conductivity analysis using three‐dimensional microstructures of gelation freezing derived cellular mullite

The relationship between thermal conductivity and unidirectional cellular mullite microstructures created with the freeze casting route is discussed using actual three‐dimensional (3D) images, in which a homogenization method was conducted with microscopic models created from 3D images, the temperature variation in macroscopic models by the finite element method (FEM), and local heat conduction in microscopic models. The simulation results were consistent with the experimental results. This image‐based modeling technique was thus confirmed to be a strong tool for the prediction of various thermal properties of porous ceramics.     

Soft materials with graphitic nanostructures

This review article focuses on our recent studies on novel soft materials consisting of carbon nanotubes. Single-walled carbon nanotubes, when suspended in imidazolium ion-based ionic liquids and ground in an agate mortar, form physical gels (bucky gels), where heavily entangled bundles of carbon nanotubes are exfoliated to give highly dispersed, much finer bundles. By using bucky gels, the first printable actuators that operate in air for a long time without any external electrolyte are developed. Furthermore, the use of polymerizable ionic liquids as the gelling media results in the formation of electroconductive polymer/nanotube composites with enhanced mechanical properties. The article also highlights a new family of nanotubular graphite, via self-assembly of amphiphilic hexabenzocoronene (HBC) derivatives. The nanotubes consist of a graphitic wall composed of a great number of pi-stacked HBC units and are electroconductive upon oxidation. The use of amphiphilic HBCs with functional groups results in the formation of nanotubes with various interesting properties.     

Interface characterization of duplex metal-coated SiC fiber-reinforced Ti-15-3 matrix composites

The interfacial reaction behavior of duplex metal (Cu/Mo and Cu/W)-coated SiC (SCS-6) fiber-reinforced Ti-15-3 composites, before and after thermal exposure, has been studied. The effect of thermal exposure on the shear sliding resistance of these composites was also obtained using a thin-specimen push-out test. The results are compared to those of an original SiC (SCS-6) fiber-reinforced Ti-15-3 composite. The interfacial reaction behavior is strongly affected by the existence of a coating layer. Both the Cu/Mo and Cu/W coating layers prevent the growth of a reaction layer. However, the coatings could not effectively prevent diffusion of alloying elements; only the W layer exists after the thermal exposure. On the other hand, the interface shear sliding stress minimally depends on the duplex metal coating layers prior to the thermal exposure, and this sliding stress in both the SiC/Cu/Mo/Ti-15-3 and SiC/Cu/W/Ti-15-3 composites decreases slightly relative to that in the SiC/Ti-15-3 composite. After thermal exposure, the interface shear sliding stress increases for the SiC/Ti-15-3 composite. In distinction, the interface shear sliding stress significantly decreases after thermal exposure in both the SiC/Cu/Mo/Ti-15-3 and SiC/Cu/W/Ti-15-3 composites. Theses behaviors are attributed to the decrease of radial clamping stress, which originates from a volume expansion associated with the β → α phase transformation.