In Situ Observation of Phase Separation of a Barium Borate Melt in a Stable Immiscibility Region under Microgravity

The precipitation of droplets was directly observed on a BaO–B₂O₃ melt in a drop shaft experiment. This is the first time that precipitation of droplets has been observed in a 4.5 s drop test. The melt film of 4BaOz96B₂O₃ (mol%) held on a platinum wire loop was heated above the critical tem-perature to produce uniformity and was cooled down to the phase separation temperature range. Phase separation of the melt was observed directly with a video camera. The IR image of the melt was simultaneously detected with a CCD array and was converted into a two-dimensional thermograph.     

Nitrogen incorporated diamond-like carbon films by microwave surface wave plasma CVD

Nitrogen incorporated diamond like carbon films have been deposited by microwave surface wave plasma chemical vapor deposition (MW-SWP-CVD), using methane (CH₄) as the source of carbon and with different nitrogen flow rates (N₂ / CH₄ flow ratios between 0 and 3). The influence of the nitrogen incorporation on the optical, structural properties and surface morphology of the carbon films were investigated using different spectroscopic techniques. The nitrogen has been incorporated into DLC:N films which was confirmed by the X-ray photoelectron spectroscopy (XPS) measurement. Moreover, the nitrogen incorporation was accompanied by a variation in the optical gap, which was attributed to the removal or creation of band tail states.     

Polymerization of propylene over metal oxides-supported TiCl3 catalysts

Summary Several metal oxides-supported TiCl₃ catalysts were prepared and propylene polymerization was conducted over them without cocatalysts. It was found that isotactic polymerization of propylene took place effectively over them.     

Polymerization of propylene over titanium exchanged Y-zeolite

Summary It was found that isotactic polymerization of propylene took place over titanium ion-exchanged Y-zeolite without organometallic compounds. The results obtained have led to the conclusions that Ti⁴⁺ species as well as Ti³⁺ species are active for the polymerization and that neither Ti-alkyl bonds nor Cl ligands are necessarily essential for polymerization of propylene.     

Synthesis of nitrogen incorporated diamond-like carbon thin films using microwave surface-wave plasma CVD

Nitrogenated diamond-like (DLC:N) carbon thin films have been deposited by microwave surface wave plasma chemical vapor deposition on silicon and quartz substrates, using argon gas, camphor dissolved in ethyl alcohol composition and nitrogen as plasma source. The deposited DLC:N films were characterized for their chemical, optical, structural and electrical properties through X-ray photoelectron spectroscopy, UV/VIS/NIR spectroscopy, Raman spectroscopy, atomic force microscope and current–voltage characteristics. Optical band gap decreased (2.7 to 2.4 eV) with increasing Ar gas flow rate. The photovoltaic measurements of DLC:N / p-Si structure show that the open-circuit voltage (V_oc) of 168.8 mV and a short-circuit current density (J_sc) of 8.4 μA/cm² under light illumination (AM 1.5 100 mW/cm²). The energy conversion efficiency and fill factor were found to be 3.4 × 10^{− 4}% and 0.238 respectively.     

Optical Properties of Dysprosium-Doped Low-Phonon-Energy Glasses for a Potential 1.3 μm Optical Amplifier

Dysprosium-doped glasses were prepared in the system of gallium-based sulfide, tellurite, zirconium-baed and indium-based fluorides and their optical properties were studied. From the absorption cross sections of five f-f bands, three Judd-Ofelt parameters, ω _t ( t = 2, 4, 6), of Dy³⁺ ion were determined. The compositional variaton of the ω₂value showed the order sulfide > tellurite > fluorozirconate > fluoroindate, whereas the ω₆ value showed the opposite tendency. Compositional variaton of the fluorescence intensity ratio of the (⁴F_9/2⁶H_13/2)/(⁴F_9/2)→⁶H_15/2) is explained by the ratio of ω₂/ω₆ of doped Dy³⁺. The emission probabilities A and the branching ratio β from ⁶H_9/2 and ⁶F_11/2 levels, which are the doublet initial level of the 1.3 μm luminescence, were calculated for the glasses, and it was found that both values showed a tendency similar to that of ω₂ against the glass composition. In the sulfide glass, A was 2.6 × 10³S^-1 and β was 93%, both the highest in all of the glasses investigated. By 1.06 μm pumping of a Nd: YAG laser, the sulfide glass showed strong 1.3 μm emission and the lifetime was 25 μs, resulting in a quantum efficiency of 7%. This value is higher than that of the Pr³⁺:¹G₄ level in ZBLAN glass with β= 60%.     

Phase Separation in Gelling Silica–Organic Polymer Solution: Systems Containing Poly(sodium styrenesulfonate)

Phase separation which occurs in parallel to the hydrolysis and gelation of alkoxysilane solution containing poly(sodium styrenesulfonate) (NaPSS) has been investigated. Depending on the reaction conditions, gel morphologies such as isolated pores, particle aggregates, and interconnected continuous pores from 0.1 to 100 μm long have been observed. Time-resolved light scattering of gelling solution suggested the occurrence of spinodal phase separation through the polymerization of silica and the subsequent freezing of the developing structure by sol-gel transition. The effects of reaction parameters on the periodic size are explained mainly in terms of their influence on the "chemical cooling" rate which is determined by the polymerizatica rate of silica and the solubility of NaPSS in the reacting solution.     

Control of molecular weight distribution of isotactic polypropylene obtained by a MgCl2-supported TiCl4 catalyst

It is of great importance in propene polymerization to control molecular weight and molecular weight distribution as well as isotacticity. Propene polymerization was carried out with an isospecific MgCl₂/TiCl₄-Cp₂TiMe₂ catalyst in the presence of various kinds of external Lewis bases. It was found that the molecular weight distribution of the isotactic polymer could be controlled while retaining high activity, high isospecificity and high molecular weight only by changing the kind and/or amount of the Lewis bases. © 1997 Elsevier Science Ltd.     

Spatial distribution of silica fillers in phase-separated rubber blends investigated by three-dimensional elemental mapping

The distribution of nano-sized silica in binary rubber blends is characterized by scanning transmission electron microscopy (STEM) tomography combined with energy dispersive X-ray spectrometry (EDX). 3D distribution of silica is visualized by STEM-EDX tomography with the tilt-series of silicon elemental maps, while the phase-separated morphologies of polyisoprene rubber (IR) and styrene-butadiene rubber (SBR) are visualized by STEM-tomography in high-angle-annular-dark field (HAADF) mode. The combination of STEM-EDX and STEM-HAADF tomography enables us to determine the distribution of silica between the two rubber phases quantitatively even with high contents of silica up to 70 phr (weight parts per hundred rubber). It is found that silica is preferentially distributed in the SBR phase, but it is also distributed in the IR phase when the IR fraction in the total rubber components is higher than 40 wt%. The preferential distribution of silica in the SBR phase improves the dispersion of the IR domains. This is the first use of this technique for a multicomponent polymer system, showing the advantage to characterize the complicated multicomponent polymer composite morphologies.     

Shrinkable Nanotubes for Duplex Formation of Short Nucleotides

Molecular monolayer nanotubes produced by self‐assembly of an amphiphile modified with a 2‐nitrobenzyl group as a photoresponsive unit are able to encapsulate dinucleotides via electrostatic attraction. Upon photoirradiation, the 18 nm inner diameter of the nanotubes shrinks to less than 2 nm as a result of photochemical cleavage of the 2‐nitrobenzyl group in the amphiphile. This shrinking of the nanotube channels leads to a propulsive release of the dinucleotides into the bulk solution and simultaneously accelerates formation of the dinucleotide duplexes. The larger nanotube channels without photoirradiation merely release each dinucleotide into the bulk solution, indicating that the squeezing via transportation in the narrow nanotube channels is necessary for duplex formation. In addition to the size effect, water with a lower polarity confined within the narrow nanotube channels helps to stabilize the energetically unfavorable hydrogen‐bonded base pair between the dinucleotides. This system should enable researchers to perform biological reactions that occur only in specific environments and conditions in living organisms.