High temperature zone‐drawing of nylon 66 microfiber prepared by CO2 laser‐thinning

A high temperature zone‐drawing method was applied to a nylon 66 microfiber, obtained by using CO₂ laser‐thinning, to develop its mechanical properties. The microfiber used for the high temperature zone‐drawing was prepared by winding at 150 m min^?1 the microfiber obtained by irradiating the laser at 4.0 W cm^?2 to an original fiber with a diameter of 50 μm, and had a diameter of 9.6 μm and a birefringence of 0.019. The high temperature zone‐drawing was carried out in two steps; the first drawing was carried out at a temperature of 230°C at supplying and winding speeds of 0.266 and 0.797 m min^?1, the second at 250°C at supplying and winding speeds of 0.266 and 0.425 m min^?1, respectively. The diameter of the microfiber decreased, and its birefringence increased stepwise with the processing. The high temperature zone‐drawn microfiber finally obtained had a diameter of 4.2 μm, a birefringence of 0.079, total draw ratio of 4.8, tensile modulus of 12 GPa, and tensile strength of 1.0 GPa. The wide‐angle X‐ray diffraction photograph of the drawn microfiber showed the existence of highly oriented crystallites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 42–47, 2006     

Layer‐by‐layer films based on charge transfer interaction of ϕ‐conjugated poly(dithiafulvene) and incorporation of gold nanoparticles into the films

Layer‐by‐layer (LBL) self‐assembled ultrathin films were prepared via consecutively alternating immersion of substrates into solutions of electron donor, poly(dithiafulvene) (PDF), and electron acceptor, poly(hexanyl viologen) (6‐VP). The charge transfer (CT) interaction formed at solid–liquid interfaces between the backbones of the electron acceptor and donor polymers was the driving force of the alternative deposition. The sandwich heterostructure of the LBL film led to electrical anisotropy in the directions parallel and perpendicular to the film surfaces. Incorporation of gold nanoparticles into the LBL films was investigated by reducing gold ions with the PDF layers already deposited on the film surfaces, or depositing PDF‐protected gold colloidal solution as the electron donor layers directly. The influence of the gold nanoparticles on the electrical anisotropy of the LBL films was also illustrated in this research. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1608–1615, 2007     

Radiation-induced graft polymerization of functional monomer into poly(ether ether ketone) film and structure-property analysis of the grafted membrane

Radiation-induced graft polymerization of sulfo-containing styrene derivatives into crystalline poly(ether ether ketone) (PEEK) substrates was carried out to prepare thermally and mechanically stable polymer electrolyte membranes based on an aromatic hydrocarbon polymer, so-called “super-engineering plastics”. Graft polymerization of the sulfo-containing styrene, ethyl 4-styrenesulfonate (E4S) into a high crystalline PEEK substrate (degree of crystallinity: 32%) hardly progressed, whereas graft polymerization into a low crystalline PEEK substrate (degree of crystallinity: 11%) gradually progressed, achieving a grafting degree of more than 50% after 72 h. Oxygen radicals appeared in the ESR spectra of irradiated PEEK films, indicating that graft polymerization initiates from the phenoxy radicals generated by scission of PEEK main chains and proceeds so as to yield block type grafts. The PEEK-based polymer electrolyte membrane (PEM) converted by aqueous hydrolysis of grafted films exhibited mechanical strength (100 MPa), being 88% of the original PEEK substrates. These mechanical properties of PEEK-based PEM are much higher than those of graft-type fluorinated PEM reported previously and almost three times higher than that of Nafion (35 MPa). Wide- and small-angle X-ray scattering (WAXS and SAXS) indicated that the graft polymerization was accompanied with recrystallization of the amorphous phase of PEEK substrate, the well known solvent-induced recrystallization of amorphous PEEK solids, to form a weak lamellar structure with 8 nm spacing. Complementary SAXS and small-angle neutron scattering (SANS) observations clearly showed that the graft-type PEEK membranes possessed ion channel domains with the average distance of 13 nm, being larger than that of Nafion. Furthermore, there was a micro-structure in the ion channels with the average distance of 1.8 nm.     

The alkylation of naphthalene over three-dimensional large pore zeolites: The influence of zeolite structure and alkylating agent on the selectivity for dialkylnaphthalenes

In order to elucidate how zeolite structure and alkylating agent play roles in the shape-selective catalysis, the alkylation, i.e., isopropylation, sec-butylation, and tert-butylation, of naphthalene (NP) was examined over three-dimensional twelve-membered (12-MR) zeolites, Y (FAU), Beta (BEA), and CIT-1 (CON), and compared to that of H-mordenite (MOR). The β,β-selectivities (for β,β-dialkylnapthalene (β,β-DAN)) and the 2,6-selctivities (for 2,6-dialkylnaphthalene (2,6-DAN)) among DAN isomers varied with the types of zeolites and alkylating agents. FAU, BEA, and CON gave only low selectivities for 2,6-diisopropylnaphthalene (2,6-DIPN) in the isopropylation, and predominant isomers were bulky and thermodynamically unstable ,β-DIPN (1,3-, 1,6-, and 1,7-DIPN) and ,-DIPN (1,4- and 1,5-DIPN) at lower temperatures, and the formation of the less bulky and thermodynamically stable β,β-DIPN (2,6- and 2,7-DIPN) increased with increasing the temperature: they have quite different features from the shape-selective catalysis over MOR. These results suggest that FAU, BEA, and CON are not shape-selective in the isopropylation, and that the isopropylation is principally controlled kinetically at lower temperatures, and thermodynamically at higher temperatures.

The β,β-selectivities over FAU, BEA, and CON increased with increasing the bulkiness of alkylating agents, and were almost 100% in the tert-butylation. On the other hand, the 2,6-selectivities over these zeolites were much lower than those over MOR at a typically moderate temperature, 250 °C. These results mean that FAU, BEA, and CON have the shape-selective nature to give the less bulky isomers, β,β-DAN, in the sec-butylation and tert-butylation by using bulkier alkylating agents, particularly 2-methyl-2-propene: they can differentiate β,β-DAN from their isomers at the transition states by the steric restriction of zeolite channels. However, the channels of these zeolites are too large for differentiating 2,6- and 2,7-DAN even with 2-methyl-2-propene.     

Cerium ion redox system in CeO2–xFe2O3 solid solution at high temperatures (1,273–1,673 K) in the two-step water-splitting reaction for solar H2 generation

CeO₂–xFe₂O₃ (x = 0.026–0.214) solid solutions with different Ce:Fe mole ratios (Ce:Fe = 9.5:0.5–7.0:3.0) were prepared as reactive ceramics with the combustion method for solar hydrogen production. The prepared CeO₂–xFe₂O₃ solid solutions were characterized by X-ray diffractometry, ICP atomic emission spectrometry, and Mössbauer spectroscopy. Two-step water-splitting reaction with the CeO₂–xFe₂O₃ solid solution proceeded at 1,673 K for the O₂-releasing reaction and at 1,273 K for the H₂-generation reaction by irradiation of an infrared imaging lamp as a solar simulator. The amounts of H₂ gas evolved in the H₂-generation reaction with CeO₂–xFe₂O₃ solid solutions were 0.97–1.8 cm³/g, the evolved H₂/O₂ ratio was approximately equal to 2 of the stoichiometric value. The amounts of H₂ and O₂ gases were independent of the Ce:Fe mole ratio in the CeO₂–xFe₂O₃ solid solution. It was suggested that the O₂-releasing and H₂-generation reactions with the CeO₂–xFe₂O₃ solid solution were repeated with the reduction and oxidation of Ce⁴⁺–Ce³⁺ enhanced by the presence of Fe³⁺–Fe²⁺.     

Preparation of carbon microcoils by catalytic methane hot-wire CVD process

Three-dimensional (3D) double-helix carbon microcoils (CMCs) were synthesized by the catalytic pyrolysis of methane using Ni catalyst in various hot-wire CVD processes. The most effective process is: using preheating method, in which methane was preheated at 1500 °C in a upper reaction tube by a hot wire, and chemical vapor deposition of carbon then occurred at 700-750 °C in a lower reaction tube, where CMCs were synthesized. The growth morphologies and microstructure were examined and compared with the conventional CMCs grown by acetylene catalytic pyrolysis.     

CuAl1 − xInxSe2 solid solutions: Dielectric function and inter-band optical transitions

The dielectric function of bulk CuAl_1 − xIn_xSe₂ with composition x varying from x = 0.07 to x = 0.6 were studied over the photon energy region 1.0-6.0 eV at room temperature by spectroscopic ellipsometry. Information on the inter-band optical transitions was obtained from the results of the standard critical point analysis of the obtained dielectric function. With increasing Indium content, all spectral features of the obtained dielectric functions were found to gradually shift towards lower energies. The details of this shift for each critical point retrieved from the obtained dielectric function were disclosed. A compositional dependence of the optical transitions in Γ point of the Brillouin zone was verified to be strong. Such dependence for N and T points turned out to be weak by comparison. The later fact was accounted for a small compositional shift of the conduction band states in N and T points as compared to Γ point.     

Note: innovative demodulation scheme for coherent detectors in cosmic microwave background experiments

We propose an innovative demodulation scheme for coherent detectors used in cosmic microwave background polarization experiments. Removal of non-white noise, e.g., narrow-band noise, in detectors is one of the key requirements for the experiments. A combination of modulation and demodulation is used to extract polarization signals as well as to suppress such noise. Traditional demodulation, which is based on the two-point numerical differentiation, works as a first-order high pass filter for the noise. The proposed demodulation is based on the three-point numerical differentiation. It works as a second-order high pass filter. By using a real detector, we confirmed significant improvements of suppression power for the narrow-band noise. We also found improvement of the noise floor.     

Characterization and properties of iron-incorporated gismondine prepared at 80°C

Iron-incorporated zeolites were successfully synthesized at a low temperature such as 80°C by choosing appropriate starting materials and characterized by inductively coupled plasma atomic emission spectrometry (ICP-AES), wide-angle X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), and magnetic susceptibility. ICP-AES showed␣that Fe component can be readily incorporated␣up to a maximum extent of Fe substitution, Fe/(Fe + Al) × 100 = 22.7%. XRD measurements suggested that the zeolites obtained have a crystal structure of gismondine type. The characterizations identified that the Fe component present in the products is all incorporated into the zeolite framework. The ammonia and water desorption profiles were compared for Fe-free and 22.7% Fe-zeolites ion-exchanged for NH₄⁺ by means of TG-MS and DSC. The ammonia desorption peak temperatures considerably shifted toward lower temperatures by the introduction of Fe, suggesting decreased solid acidity. DSC thermograms of the as-synthesized gismondines revealed that they do not contain free water (i.e., water not coordinated to cations) in the pores irrespective of the Fe content. The enhanced catalytic reactivity of the Fe-incorporated gismondines was also confirmed from the decomposition of hydrogen peroxide. An apparent activation energy of 43 kJ mol⁻¹ was obtained independent of the Fe contents in zeolites. This value was much lower than 70 kJ mol⁻¹ for the same reaction in the homogeneous solution containing iron alum as a reference sample.     

Structural studies of copper sulfide films: effect of ambient atmosphere

We examined the structural properties of copper sulfide films as a function of the sulfurization time of 70-nm-thick Cu films. Copper sulfide films with various phases such as mixed metallic Cu-chalcocite, chalcocite, roxbyite, and covellite phases were formed with increasing sulfurization time. To evaluate the structural stability of various films, all the films were exposed to the ambient atmosphere for the same amount of time. Although the phase structure and stoichiometry of the films were maintained at a greater depth, the near-surface region of the films was oxidized and covered with overlayers of oxide, hydroxide, and/or sulfate species due to the exposure and reaction with the ambient atmosphere. The oxygen uptake and its reactivity with the copper sulfide film surfaces were enhanced with increasing sulfur content of the films. In addition, the type of divalent state of copper formed on the film surfaces depended on the phase structure, composition, and stoichiometry of the films.