Water wettability/non-wettability of polymer materials by molecular orbital studies

The water wettability and non-wettability onto various kinds of polymers, which have so far been macroscopically described by the water contact angle, were investigated using the molecular orbital theory. An atomistic model consisting of an H₂O molecule and a selected polymer crystal surface was analyzed in the isolated and the physisorbed states. The degree of interaction between the water molecule and the polymer surface was evaluated by considering the change of Mulliken charge at the oxygen site in the water molecule, and also the work of adhesion during the physisorption process. Such energetic quantities for several polymers were compared with the macroscopic water wettability/non-wettability. We found fairly good agreement between these approaches for the highly non-wettability polymers.     

Dynamic viscoelastic behavior of cholesteric liquid crystalline side-chain copolymers

Summary The rheological behavior of the cholesteric side-chain copolysiloxane whose two kinds of mesogenic groups consist of cholesteryl units and biphenyl benzoate units was investigated for three different compositions: 31:69, 35:65, 37:63 (in mol%). On the frequency dependence diagram of G′ for the copolymers at various temperatures, G′ decreases with decreasing frequency. The slope of G′ in a higher frequency region at lower temperatures (110°–130°C) is similar to that in the flow region of amorphous polymer melts. However, the slope of G′ in a lower frequency region at higher temperatures (140°–160°C) is relatively small, and the G′ curves in this region can not be superposed on to a single master curve. This deviation seems to be due to change in stability of the domain structure of the cholesteric phase. Furthermore, on the temperature dependence curve of G′, G′ showed a maximum near T _c1 . This maximum of G′ curve seems to be caused by molecular organization of a blue phase.     

Property of Amorphous/Nanocrystalline Hybrid Wires of TiNi-Base Shape Memory Alloys

The microstructures and mechanical properties of amorphous/nanocrystalline hybrid TiNi wires produced by severe cold drawing were investigated. Annealed wires of Ti-50.9?mol%Ni and Ti-41?mol%Ni-8.5?mol%Cu were subjected to severe cold drawing of 50-70% reduction. The as-drawn TiNi wires were composed of the mixture of amorphous phase and predominantly B2 nanocrystalline phase. Young??s modulus increased with the drawing reduction which can be attributed to the increase in the amount of amorphous phase. For the binary TiNi wires, the volume fraction of amorphous phase was estimated to be about 60% from Young??s modulus and electrical resistivity. The wires drawn over 60% exhibited peculiar large linear elastic strain which is quite different from superelasticity. Aging at 573?K led to an increase in tensile elongation as well as in the recoverable strain. The amorphization by cold drawing was also confirmed for Ti-41?mol%Ni-8.5?mol%Cu in 62% drawn wires.     

Photoconductivity of n-type semiconductor nanoparticle-doped poly(N-vinylcarbazole) films

TiO₂, CdS and ZnS nanoparticles that disperse stably in organic solvents are synthesized. Poly(N-vinylcarbazole) films doped with the n-type semiconductor nanoparticles are prepared with a cast method. The films exhibit a transient photocurrent when irradiated by a light pulse and act such as a diode when AC voltage is applied under continuous illumination. The transient photocurrent response and diode-like properties are significantly different depending on the kind of the nanoparticles and their amounts. The films doped with TiO₂ and CdS nanoparticles increase the transient photocurrent at lower doped amounts, which is remarkable for TiO₂-doped films. Time of flight analysis of the transient photocurrent shows that mobility of hole in PVK increases with increase in the amount of CdS and TiO₂. From the studies on the diode-like properties, the current increase at lower dopant concentration is concluded to be due to increase in the amount of holes by an electron transfer from PVK to the photo-excited nanoparticles. At higher doping with CdS nanoparticles, main charge carrier of the films is found to change from holes to electrons.     

Creep cavity growth under interaction between lattice diffusion and grain-boundary diffusion

A model and a method of numerical analysis of the cavity growth in grain boundaries in metals due to lattice diffusion are proposed. The growth behavior simulated is compared to that due to grain-boundary (GB) diffusion. The simulation method is extended to analyze the growth under the interaction between lattice diffusion and GB diffusion. The growth rate calculated under the interaction is approximately equal to the linear sum of those due to the pure lattice diffusion and the pure GB diffusion.     

Development of an on-line stabilization method for local power systems with large-capacity generation plants

This paper presents an on-line stabilization control method developed with the aim of maintaining transient stability in a local power system which includes large-capacity generation plants. The characteristics of this method are that the power/angle curve is estimated from the on line active and reactive power measured at the generator terminal, and the optimum generation shedding for stabilization is determined by applying the equal area method to this curve. Simulation tests using detailed models of the power system confirmed that the optimum generation shedding for stabilization could be computed for various fault conditions, both symmetrical or asymmetrical. It was also determined that the on-line data could be sampled for several tens of milliseconds after clearing the fault. Thus, this method provides effective control logic for practical stabilizing systems.     

A possible immunosuppressant, cycloprodigiosin hydrochloride, obtained from Pseudoalteromonas denitrificans

Biochemical characteristics of spent fowl meat injected with calcium chloride or sodium chloride were evaluated. Hot-boned breast fillets were injected to 10% (wt/wt) with 0.3 M CaCl2 or 0.6 M NaCl, tumbled, and aged 24 h. Tumbling was conducted at 20 C, -635 mm Hg, 20 rpm for 1 h. Hot-boned and cold-boned (24 h) fillets were used as controls. One fillet from each carcass was baked and sheared with an Allo-Kramer cell, whereas the other fillet was used for biochemical analysis. Shear values indicated that both CaCl2- and NaCl-treated samples had significantly (P < 0.05) lower shear values than hot-boned controls but were similar (P > 0.05) to cold-boned samples. The CaCl2 injection treatment significantly elevated (P < 0.05) the tissue calcium content compared to all other treatments. There was no significant difference in heat-stable collagen content (P > 0.05) among all treatments, which indicated that CaCl2 or NaCl did not contribute to meat tenderness through degradative changes in collagen. Calpain data indicated that mu-calpain had disappeared by 24 h aging in all treatments. The m-calpain activity was significantly lower (P < 0.05) in samples treated with CaCl2 than in the other samples. The NaCl-treated samples had m-calpain activity similar (P > 0.05) to that of hot-boned controls. Sarcomeres of CaCl2-treated samples were significantly shorter (P < 0.05) than those of cold-boned controls, were similar (P > 0.05) to those of hot-boned controls, and were shorter than those of NaCl-treated muscles. The sarcomere length and calpain data suggest that CaCl2 tenderized fillets by ionic strength and calcium-specific effects (possibly a proteolytic action), whereas the NaCl solution tenderized by ionic strength effect at a similar conductivity level to that of the CaCl2 solution.     

A rheo-optical study on the reformation of structure in racemic poly(γ-benzyl glutamate) liquid crystals

Transmitted light intensities were measured by means of the polarized light technique for the nematic liquid crystal phase of racemic poly(γ-benzyl glutamate) (PBG) in m-cresol at 25°C after cessation of steady flow at shear rates ranging from 0.2 to 110 s^?1. Weight-average molecular weights of PBG used were 1.5, 2.1, and 2.6 × 10⁵, while the concentrations varied between 20, 30, and 40 wt percent. Transmitted light intensities with crossed and parallel polarizers, I_x and I_|, show wavy changes with time after cessation of steady flow, indicating the retardation decreases with time. An attempt was made to explain experimental results on the basis of a simple model, in which not only relaxation of molecular orientation but also effects of the wall and disclination were taken into account.     

Impedance characteristics of double-hetero structure laser diodes

The effects of the onset of lasing on the I-V characteristics, the impedance characteristics and the light modulation characteristics of laser diodes have been discussed by introducing the rate equations which involve carrier diffusion process in the active layer interacting with the radiation field intensity. The static I-V characteristics exhibit a kink at lasing threshold current, reflecting the decrease of effective lifetime of carriers. Effective carrier lifetimes decrease with increasing light intensity, which results in a steep attenuation of injected carrier density in the active region. The impedance and light modulation characteristics are obtained in the small signal approximation. The small signal light modulation characteristics depend strongly on whether the laser diode is excited by the constant current modulation or the constant voltage modulation. The impedance is changed drastically by the onset of lasing and exhibits a resonance which coincides exactly with the optical modulation resonance frequency.