General description of mechanical anisotropy of semicrystalline polymers in relation to orientation of structural units composed of crystalline and noncrystalline materials

A mathematical representation of the transformation of an orientation function between two sets of Cartesian coordinates is discussed in terms of a series expansion of the distribution function in generalized spherical harmonics. A general procedure for calculating the mechanical anisotropy of a single-phase system (a polycrystalline material) from the orientation of its structural units and the intrinsic mechanical anisotropy of the structural unit is discussed in relation to the transformation of the orientation distribution function, i.e., mutual conversion of the coefficients in the expansion of the distribution function between the two sets of Cartesian coordinates. The procedure is extended to a two-phase systems (semicrystalline polymers) containing structural units composed of crystalline and noncrystalline materials in three different geometrical arrangements.     

Light scattering from tilted two-dimensional spherulites

The theory of small-angle light scattering was developed for oblique incidence of the light beam on the surface of a two-dimensional spherulite. Results of the theory were compared with previously reported results of light scattering from two-dimensional and three-dimensional spherulites for normal incidence, and with some experimental patterns. The comparisons suggest that the scattering intensity distributions of two-dimensional spherulites deviate from those of three-dimensional spherulites when the sample surface is tilted with respect to the propagation direction of the incident beam, although they are almost identical when the sample surface is normal to the incident beam. Observation of the change of scattered intensity distributions upon tilting the samples thus provides a method of distinguishing between two-dimensional and three-dimensional spherulites. Moreover, this observation makes it possible to determine the degree of planar orientation of the optic axes of optically anisotropic scattering elements within two-dimensional spherulites. The calculations were carried out for special cases of two-dimensional spherulites with the optic axis orientation confined to the two-dimensional plane and randomly or helicoidally rotated around the spherulite radii.     

Molecular aggregation of solid aromatic polymers. I. Small-angle x-ray scattering from aromatic polyimide film

Molecular aggregation in a commercial polyimide film, Du Pont Kapton, was investigated by small-angle x-ray scattering (SAXS). From the analysis of the desmeared SAXS curve, it is concluded that aggregation in the Kapton film can be elucidated in terms of a two-phase structure having electron density fluctuations within the phases. For comparison with the molecular aggregation in Kapton, molecular aggregation in polyimides synthesized in our laboratory was also investigated. It was found in this case that molecular aggregation is controlled by the initial imidization temperature. Molecular aggregation of polyamic acid and polyimide cyclized at a low temperature gives amorphous structures. On the other hand, molecular aggregation of polyimide cyclized at high temperatures gives two-phase structures like that of Kapton film. The SAXS curve for a polyimide having the two-phase structure shows a peak due to interference between ordered regions. The two-phase structure of the polyimide can be explained in terms of a one-dimensional model. The more ordered phase is produced at the higher initial imidization temperature. The relative density difference between two phases is only a few percent for polyimide films cyclized at high temperatures. This result shows that the two-phase structure of aromatic polyimide differs essentially from that of ordinary crystalline polymers.     

Pair breaking parameter of two-dimensional dirty superconductors

Intrinsic mechanism of pair breaking is given for dirty superconducting films. Dynamical interaction between electrons such as Coulomb interaction plays an essential role. The diffusion processes of both density- and pair-fluctuations are also important. The problem of the Thompson's parameter for the Maki term of fluctuation conductivity is solved and the correct dependence of the parameter of the sheet resistance R_sq is given.     

Selective oxidation of semiconducting single-wall carbon nanotubes by hydrogen peroxide

Selective oxidation of single-wall carbon nanotubes (SWCNTs) by H2O2 was conducted at varying heating times and monitored by UV-vis-NIR spectroscopy. A major increase in the relative absorption intensity indicated a higher than 80% concentration of metallic SWCNTs in the final product. Here, it is suggested that semiconducting SWCNTs are more reactive than metallic SWCNTs because of hole-doping by H2O2, resulting in faster oxidation.     

Intramolecular bromo-amination of 1,4-cyclohexadiene aminal: one-pot discrimination of two olefins and concise asymmetric synthesis of (-)-gamma-lycorane

The reaction of cyclohexa-2,5-dienyl-1-methylaldehyde and optically pure 1,2-diaryl-1,2-diamine followed by intramolecular bromo-amination produced a one-pot discrimination of two olefins in the cyclohexane system, which was used for the asymmetric synthesis of (-)-gamma-lycorane.     

A novel strategy for fluorescence enhancement in the solid-state: affording rigidity to fluorophores packing

Solid-state fluorescence enhancement was achieved by preparation of rigid packing that was afforded by disposition of benzylamine into tubulate spaces, serving as a powerful and useful strategy for the enhancement.     

Elastic heterogeneity in metallic glasses

When a stress is applied on a metallic glass it deforms following Hook's law. Therefore it may appear obvious that a metallic glass deforms elastically. Using x-ray diffraction and anisotropic pair-density function analysis we show that only about 3/4 in volume fraction of metallic glasses deforms elastically, whereas the rest of the volume is anelastic and in the experimental time scale deform without resistance. We suggest that this anelastic portion represents residual liquidity in the glassy state. Many theories, such as the free-volume theory, assume the density of defects in the glassy state to be of the order of 1%, but this result shows that it is as much as a quarter.     

Electrical breakdown of microwave plasma in water

The electrical breakdown of microwave plasma in water was investigated between 1 and 30 kPa. The dependency of the ignition power for generating plasma on the size of coaxial electrode was measured. The ignition power decreases with a decrease of the diameter of the inner electrode. The behavior of microwave plasma in water was observed using a high-speed camera. The plasma ignites in a bubble generated by microwave heating. The model for calculating the electric field was created on the basis of the captured images of the bubble just before plasma ignition. The method presented can be used to visualize the electrical field distribution in the bubble. The electric field breakdown was calculated using the measured ignition power. The electric field breakdown of plasma in water is of the same order as gas phase plasma.