Photoinduced electron transfer in nanostructures of ultrathin polyimide films containing porphyrin moieties

Photoinduced electron transfer between porphyrin moieties and pyromellitimide fragments has been investigated in multi-layered structures of ultrathin polyimide films prepared by the Langmuir-Blodgett (LB) technique. The LB films were composed of three kinds of polyimides, which contained zinc tetraphenylporphyrin (ZnTPP) unit as an electron donor (D-layer), no chromophoric groups (S-layer), and pyromellitimide fragments as an electron acceptor (A-layer). The layered structure and orientational distribution of porphyrin moieties in the LB films were evaluated by surface plasmon measurement and absorption dichroism measurement, respectively. The thickness of monolayer was estimated to be 0.9 nm for the polyamic acid films and 0.4 nm for the polyimide films. The molecular plane of porphyrin moieties was oriented in the direction parallel to the substrate plane. In the multi-layered structures of polyimide LB films, the efficiencies of photoinduced electron transfer from porphyrin moieties to pyromellitimide fragments varied sharply with the number of spacing layers, indicating that the short-range interactions such as electron transfer could be controlled by the fabric of ultrathin films. The rate of electron transfer observed by the fluorescence quenching measurements was numerically simulated for the nanostructure using the Monte Carlo method.     

Direct synthesis of highly crystalline single-phase hexagonal tungsten oxide nanorods by spray pyrolysis

The metastable state hexagonal-tungsten oxide (h-WO₃) has been attracting attention over the past decade because of its high reactivity that arises from the hexagonal channels in its crystal structure. Simplification of the process used to synthesize h-WO₃ is an important step to facilitate the industrial applications of this material. In this study, we addressed this challenge by developing a spray pyrolysis process to synthesize highly crystalline h-WO₃. The ratio of the monoclinic to the hexagonal phase was controlled by adjusting the segregation time. Single-phase h-WO₃ nanorods were synthesized using a carrier gas flow rate of 1?L/min, which was equivalent to a segregation time of 18.4?s. The ability of the h-WO₃ nanorods to adsorb nitrogen and carbon dioxide was evaluated to confirm the presence of hexagonal channels in the crystal structure.     

Snoek relaxation in a copper-precipitated alloy steel

We studied the effect of thermal embrittlement of a steel containing 1.29 at% copper on the Snoek relaxation. The hardness increased with isothermal aging at 723 K and decreased after showing a maximum. Hardness change is governed by bcc–copper clusters precipitated from the ferrite iron crystal. Using a forced-vibration torsion-pendulum method, we studied the internal-friction spectrum and recovery of the maximum relaxation strength after quenching from 723 K. We observed a broad nonsymmetrical spectrum which apparently consists of three Debye peaks. With higher hardness, the recovery rate increased. We interpreted our results in terms of Nowick’s theory of interstitial/substitutional-solute interactions. For recovery, we used the Cottrell–Bilby–Harper t^2/3 model.     

Ultrasonic attenuation monitoring of fatigue damage in low carbon steels with electromagnetic acoustic resonance (EMAR)

We studied microstructure evolution during tension-compression fatigue in low carbon steels, containing C: 0.15 mass%. In situ monitoring of axial-shear-wave attenuation and velocity was achieved with electromagnetic acoustic resonance (EMAR), which is a combination of the resonant spectroscopy technique and a noncontacting electromagnetic acoustic transducer (EMAT). Transduction occurs with the magnetostriction effect and is the key to establish a continuous monitoring of microstructural changes in the surface region of the metals with high sensitivity. We found for the first time that the attenuation is highly sensitive to the accumulated fatigue damage, showing a minimum around 20% of the whole life. This phenomenon is interpreted in terms of drastic change of dislocation mobility and rearrangement, which is supported by TEM observation for dislocation structure. This technique has the potential to assess the damage advance and to predict the fatigue life of metals.     

Ion-induced nucleation rate measurement in SO2/H2O/N2 gas mixture by soft X-ray ionization at various pressures and temperatures

This paper reports the systematic investigation of ion-induced nucleation rate measurement in a SO₂/H₂O/N₂ gas mixture, employing soft X-ray at different pressure and temperature levels. Experiments were conducted using a modified continuous flow gas-generation system employing a soft X-ray ionizer and a particle counter, with an improved integrated online temperature, pressure and a relative humidity (RH) control system. Nucleation rates were measured as a function of SO₂ concentration at different levels of RH, pressure (600–970 hPa) and temperature (5–25 °C). The results show that the nucleation rate dependence on SO₂ concentration followed a power law, and the slope varied slightly in a range from 1 to 1.26 at different RH levels (15–60%). A positive pressure effect was generally found and a power law was followed with varied scaling for different SO₂ concentrations. The trend of an increase in nucleation rate with temperature was consistent with observations in homogenous nucleation experiments, and with the behavior predicted by classical binary nucleation theory. These experimental results will be useful to explain the contribution of ion-induced nucleation in different locations and atmospheric conditions.     

A stochastic approach for continuous and discontinuous crack growth in polycarbonate under cyclic loading

This article presents a stochastic approach to predict fatigue crack propagation (FCP) diagrams of continuous crack growth (CCG) and discontinuous crack growth (DCG) in polycarbonate (PC) under cyclic loading. First, it is assumed that the macroscopic fatigue crack propagates stochastically. The transition probability is then expressed in conjunction with the craze fibril breakdown model for CCG. Second, the stochastic process is applied to DCG assuming that DCG occurs because of an unstable crack growth in the craze zone. A fracture criterion using a stress intensity factor is introduced for the unstable crack growth. As a result, we obtain an FCP diagram where the rate in CCG is lower than that in DCG. The stress intensity factor range for the DCG–CCG transition can be theoretically determined. Finally, to verify the present approach, the experimental data of DCG and CCG of PC are fitted to the Paris equation. In addition, the relationship between the DCG band size and the number of cycles required for DCG is predicted in order to compare it with the experiment data. POLYM. ENG. SCI., 2013. © 2013 Society of Plastics Engineers     

Formation of phase structure and crystallization behavior from disordered melt for ethylene-isoprene block copolymers and their blends

The structure formation and crystallization kinetics in crystallization from a disordered melt were investigated for a polyethylene-polyisoprene block copolymer (LEI) having M_n = 3.2 × 10⁴ and 53 wt% of polyethylene content and for its blends with the corresponding homopolymers, polyethylene (PE) and polyisoprene (PIp), using synchrotron small-angle X-ray scattering techniques (SAXS) and differential scanning calorimetry (DSC). For LEI copolymer and the blends, no microphase separation structure was observed in the molten state. In the crystalline state of the neat LEI, the first and higher order scattering peaks were clearly observed, in which the intensity of the higher order peaks was considerably strong. This unusual behavior of the higher order peaks was explained by the lamellar insertion model of Hama and Tashiro. From the analyses based on this model and one-dimensional electron density correlation function with a three phase model, the phase structure in the crystalline state of the neat LEI was concluded to be a regular lamellar structure consisting of crystalline lamella of PE block and amorphous layers of PE and PIp blocks. This phase structure was quite different from that reported previously for a polyethylene-polyisoprene block copolymer (HEI) with a higher molecular weight in which HEI crystallized with keeping the microphase separation structure in the melt. For the blends of LEI with PIp homopolymer, the phase structure is affected by the blend composition, while for the blends with PE homopolymer, the phase structure depended on the crystallization temperature as well as the molecular weight and composition of the added PE. The Avrami index was 2-3 for neat LEI, all blends and PE homopolymers.     

Influences of miscible and immiscible oils on flow characteristics through capillary tube—part I: experimental study

A capillary tube is widely used as an expansion device for small refrigeration cycles. In a practical refrigeration cycle, some amount of refrigeration oil is discharged from a compressor and refrigerant/oil mixture flows through the capillary tube. This study investigated experimentally the influence of mixing of the refrigeration oil with the refrigerant on the flow through the capillary tube. The experiments are carried out with not only a miscible combination of refrigerant and oil but also an immiscible combination. In both cases, the mass flow rate through the capillary tube and temperature and pressure distributions along the tube are measured under several conditions of subcooled degree and oil concentration. In the case of miscible combination, the mass flow rate of refrigerant decreases with increasing the oil concentration because the viscosity of liquid phase increases by the mixing of viscous oil. Even in the case of the immiscible combination, the oil droplet is so small that it mixes homogeneously in the liquid phase in the capillary tube and the refrigerant mass flow rate decreases by the mixing of immiscible oil. There is no significant influence of the oil concentration on the underpressure, which means pressure difference between saturation pressure and flash inception pressure, in both miscible and immiscible combinations.     

Strong metal-support interactions (SMSIs) between Pt and Ti3+ on Pt/TiOx nanoparticles for enhanced degradation of organic pollutant

In this work, Pt nanoparticles were deposited onto the surface of Magnéli phase titanium suboxide (TiO_x) nanoparticles using a microwave-assisted deposition method. The effect of different concentrations of Pt nanoparticles was investigated to evaluate the strong metal-support interactions (SMSIs) between Pt and TiO_x based on their performance for the degradation of organic pollutant molecules. The adsorption and catalytic performance of the as-synthesized Pt/TiO_x nanoparticles were evaluated with respect to the degradation of rhodamine B (RhB) molecules without any external energy source. The Pt/TiO_x nanoparticles with Pt loading at 10 wt% (10%Pt/TiO_x) exhibited a remarkable performance. The XPS, CV, and FTIR analyses confirmed the presence of RhB degradation reactions under dark condition. This remarkable performance of the Pt/TiO_x nanoparticles was attributed to the SMSIs between Pt and Ti³⁺ atoms, which improves their performance compared with Pt/TiO₂ nanoparticles, and high density of active sites due to their nanometer size, which results in better performance compared with that of Pt/TiO_x submicron particles.