Ceramization of Reflux-Treated Polymethylsilane Precursors to Silicon Carbide

The pyrolysis of polymethylsilane (PMS) in an argon gas environment with a flow rate of 1 L/min was investigated as a standard pyrolytic process, and the investigation showed SiSi network formation at 573 K. Subsequently, various condensed PMS resins were prepared by adjusting pre-heat-treatment or reflux conditions in the temperature range of 423–723 K. The effect of pre-heat treatment or refluxing on the ceramic yield at 1273 K was quantitatively evaluated. Structural evolution in the PMS resins prepared under various reflux conditions was investigated during pyrolysis up to 1873 K. The X-ray diffraction patterns of the pyrolysis products revealed crystallite growth of β-SiC and silicon at 1273–1473 K. ²⁹Si solid-state nuclear magnetic resonance with the single-pulse method was also conducted on the pyrolysis products at 1273 K.     

Self-Sharpening of Thin Tungsten Electrode in Single, High-Current Discharge: Its Dynamics and Mechanism

Self-sharpening of a thin tungsten electrode occurs in single, high-current discharge. This phenomenon has been observed with a custom-made, high-speed imaging system. The system allowed us to take one hundred images of the electrode shape during and after the discharge with 16 μs intervals. The following selfs-harpening mechanism has been proposed based on observations: (1) During the discharge, when the melt front descends towards the axis of the electrode, while the melt forms a sphere and moves along it due to the surface tension. (2) The melt continues moving even after the discharge, revealing a needle-shaped unmelted part and then solidifies. Detailed studies of discharge conditions to the diameter of the needle-shape formed by the process have been carried out. Results supporting the proposed mechanism are obtained.     

Vertically integrated human P450 and oxygen sensing film for the assays of P450 metabolic activities

An assaying method of cytochrome P450 (P450 or CYP) monooxygenase activities for toxicological evaluation of drugs and environmental pollutants was developed by immobilizing P450 on an oxygen sensoring layer. Membrane fractions from E. coli expressing human P450 were entrapped in agarose or silica-based gels and immobilized on 96-well microarrays having an oxygen sensing film at the bottom. The oxygen sensing film was made of an organically modified silica film (ORMOSIL) doped with Tris(4,7-diphenyl-1,10-phenanthroline) ruthenium dichloride (Ru(dpp)(3)Cl(2)). P450 activity toward the substrates was monitored through the fluorescence intensity enhancement due to the oxygen consumption by the metabolic reactions. For the metabolism of chlortoluron, a selective herbicide used to control grass weeds, CYP1A1 immobilized in agarose gel showed a higher activity and stability compared with those in silica gels and free suspensions. The luminescence changing rate evaluated by the dynamic transient method (DTM) could be correlated with the substrate concentration. We also compared the metabolic responses of human P450s (CYP1A1,CYP2C8, CYP2E1, CYP3A4) toward various substances. The use of immobilized P450 on an oxygen sensing layer provides a versatile assaying platform owing to the following features. First, the oxygen sensor can detect metabolic reactions of any P450 species, in contrast with assays using fluorogenic substrates. Second, vertical integration of the oxygen sensor and immobilized P450 enhanced the sensitivity because of the effective depletion of oxygen in the vicinity of the oxygen sensing layer. Third, immobilization enables repeated use of P450 by replacing the substrate solutions using a flow cell. Furthermore, the activity of immobilized P450 was retained at least for 3 weeks at 4 °C, suggesting its long-term stability, which is an additional attractive feature.     

Molecular or Nanoscale Structures? The Deciding Factor of Surface Properties on Functionalized Poly(3,4‐ethylenedioxythiophene) Nanorod Arrays

Nanostructures of poly(3,4‐ethylenedioxythiophene) (PEDOT) are assembled by using an anodic aluminum oxide template directly fabricated on gold‐coated silicon wafers. Inside these templates, PEDOT and hydroxy functionalized PEDOT form tubes. On the other hand, alkyl‐ and perfluoro‐functionalized PEDOTs assembled as nanorods. This approach allows a platform to understand the molecular and nanostructural effect on the surface wettability of these materials. In the water/air interface, the contact angle of water droplet (CA_water) for the smooth alkyl‐functionalized PEDOT films increases when alkyl chain gets longer. In contrast, the contact angle reachs saturation at 130° with alkyl chain longer than ethyl in assembled nanorod arrays. It remains the same even in the case of perfluoro‐functionalized PEDOT. Moreover, ethyl‐functionalized PEDOT (PEDOT‐C2) nanorods displays superoleophilicity and the oil deoplet cannot stay on the film in water. Based on the wettability studies, it is concluded that the nanostructures contribute predominantly for the surface wettability of these nanomaterials when the length of alkyl chain crosses certain threshold.     

Dispersion of multi-walled carbon nanotube using soluble polysilsesquioxane containing alkylammonium side chains and triiodide counterions

In this study, we found that 1-pentanol dispersion of multi-walled carbon nanotube (MWCNT) was obtained when ultrasonication of MWCNT was performed in 1-pentanol solution of ammonium group-containing polysilsesquioxane with triiodide anions (PSQ-I₃). Dispersibility of MWCNT in 1-pentanol was first investigated by the presence of absorption at 750 nm in UV–Vis measurements. In addition, the number-average particle size estimated by dynamic light scattering measurement of 1-pentanol dispersion of MWCNT/PSQ-I₃ was assessed to be 120.3 ± 34.8 nm. The dispersion passed through a membrane filter with ca. 7 μm pores, indicating that large MWCNT aggregates in micrometer scale did not exist in 1-pentanol. Furthermore, the transmission electron microscopy image of the sample obtained by drying 1-pentanol dispersion of MWCNT/PSQ-I₃ showed many lines with ca. 10 nm diameter derived from MWCNT, indicating that MWCNTs were individually dispersed in PSQ matrix.     

Epitaxial growth of chromium carbide nanostructures on multiwalled carbon nanotubes (MWCNTs) in MWCNT–copper composites

We have, for the first time, fabricated chromium (Cr) carbide nanostructures on multiwalled carbon nanotubes (MWCNTs) in a MWCNT–copper (Cu) composite by adding small amounts of Cr. A single nanocrystal of carbide was epitaxially grown on the sidewall of chemically treated MWCNTs through the diffusion of solute Cr atoms to defects in the MWCNTs. Carbide has an island-shaped morphology with a maximum size of several hundred nanometers. The phase of the generated Cr carbide nanostructures was mostly Cr₇C₃, as determined by electron beam diffraction using the nanobeam diffraction mode of a transmission electron microscope. In particular, the Cr carbide nanostructures formed at radially unzipped sites were connected to the outermost wall and some inner walls of the MWCNTs. This is expected to increase the load-bearing capacity of the MWNCTs because the inner walls contribute to the load transfer, which is very effective for improving the mechanical and thermomechanical properties of the composites.