Noriyuki Yoshimoto

Ultrasonic velocity measurement of crystallization rates of palm oil in oil-water emulsions

Abstract The xrystallization behaviour of palm oil dispersed in oil-in-water emulsion (oil, 30 wt.%; water, 70 wt.%) was studied by ultrasonic velocity measurement under cooling and heating processes. Na caseinate, as a major surfactant, and hydrophilic sucrose polyesters, as minor components, were employed for emulsification. The rates of crystallization of palm oil were monitored by the changes in the ultrasonic velocity values, which increasing amount of fat crystals in the palm oil phase. Effects of the addition of highly hydrophobic food emulsifiers of sucrose polyesters with HLB values of around 1, added in palm oil, were examined, in an attempt to modify the rate of crystallization of palm oil. Comparing the results in the emulsion systems with those in neat palm oil liquid, we have obtained the following results: (a) the rates of crystallization, particularly of nucleation, were retarded in the emulsion systems compared with the neat liquid; (b) the addition of hydrophobic sucrose polyesters increased the nucleation rates in the emulsion systems, whereas it retarded the rates of crystal growth; (c) this opposing effect was most manifest for the sucrose polyesters with a stearic acid moiety, yet minimized for those with an oleic acid moiety. A mechanistic argument is given for the experimental results in terms of emulsifier-fat interactions.

Effect of particle size reduction on crack formation in electrophoretically deposited YBCO films

Fabrication of superconducting films by an electrophoretic deposition technique has promising industrial applications. However, there are several problems in the case of electrophoretic deposition for fabrication of superconducting films, the major one being crack formation in the films. We examined the effect of particle size reduction on crack formation. The microstructures of films were determined by scanning electron microscopy. Crack in films deposited from a colloid consisting of submicron-sized particles was much less than that in films deposited from a colloid consisting of micron-sized particles. The particle size reduction improved the morphology of superconducting films fabricated by the electrophoretic deposition technique.

Oligothiophene Self-Assembly on the Surface of ZnO Nanorods: Toward Coaxial p–n Hybrid Heterojunctions

We describe herein the design, synthesis and detailed structural characterization of hybrid 1D nanostructures. They are prepared by supramolecular self-assembly of oligothiophene molecules on the surface of zinc oxide nanorods in solution at room temperature. Electronic absorption spectroscopy and X-ray diffraction show that both organic and inorganic components in the coaxial p-n heterojunctions are crystalline. Especially, it is demonstrated that the organic compounds form a self-assembled monolayer at the surface of the nanorods, which is not the case when zinc oxide quantum dots are instead used. As a result of their hybrid nature, the 1D nanostructures lead to ambipolar semiconducting nanostructured materials as active layers in field-effect transistors.

Sound Velocity Measurements of Molten Germanium

The temperature dependence of the sound velocity of molten germanium was measured up to 1200° C using a newly developed high-temperature ultrasonic measurement system. The system is based on the phase-comparison method and provides highly precise sound-velocity measurement. The temperature dependence of sound velocity of molten germanium showed softening near the melting temperature during both heating and cooling processes. This could be attributed to microscopic structural changes in the liquid.

In Situ Real-Time X-Ray Diffraction During Thin Film Growth of Pentacene

In situ and real-time observation of 2-dimensional grazing incidence x-ray diffraction (2D-GIXD) during growth of pentacene thin films were carried out using a newly home-built portable vacuum deposition chamber using synchrotron radiation at SPring-8. Crystal growth and successive polymorphic transformation from thin film phase to bulk phase are clearly observed at room temperature and 75°C. A distinct orientation of bulk phase characterized by tilted (001) plane is found in the grown thin films at room temperature.

Epitaxial Relationships of Para-Sexiphenyl Thin Films on Alkali Halide Substrates

The dependence of substrates on the epitaxial relationships of vapor deposited thin films of p-sexiphenyl(p-6P)was investigated by X-ray diffractmetry. The cleaved(001)surfaces of single crystals of NaCl, KCl and KBr were used for the substrate. The temperature dependence of the film structure was also examined between 50°C and 170°C. The epitaxial relationships of both standing and lying orientations were determined for the films grown on each substrate. The observed complex patterns of in-plane orientations were explained in terms of misfit ratio.

Giant Seebeck effect in pure fullerene thin films

The small thermal conductivity of molecular solids is beneficial for their thermoelectric applications. If Seebeck coefficients were sufficiently large to compensate for the relatively small electrical conductivity, these materials would be promising candidates for thermoelectric devices. In this work, the thermoelectric properties of C60 were studied by in situ measurements under ultrahigh vacuum after the deposition of a pure C60 thin film. An exceptionally large Seebeck coefficient of more than 150 mV/K was observed as a steady-state thermoelectromotive force. Even considering several extreme but realistic conditions, conventional semiclassical thermoelectric theories cannot explain this giant Seebeck effect.

Elastic and Magnetic Properties of Bilayer Manganites: La2-2xSr1+2xMn2O7 for x=0.35 and 0.40

We have grown single crystals of LSMO(327) for x =0.35 and x =0.40 and investigated the elastic properties systematically, together with the electrical resistivity, magnetoresistance and magnetizat...

Thermal treatment effects of molten BaB2O4 on crystallization and transformation

Abstract The effect of thermal treatment of molten BaB2O4 on crystallization and subsequent solid state transformation were studied. A series of different thermal treatment conditions were employed and the starting material was switched from one modification to the other. No effects were found on the crystallization phenomena, although the melt has been suspected to contain partially the crystal structure after melting. An anomalous behavior that the low temperature phase preferentially crystallized at the metastable temperature region may be explained in terms of the contribution of molar volume term in the classical equation of the nucleation to the metastable phase. Transformation from the β-form to the α-form was accelerated when the starting β-form was prepared from the melt which had been treated at high temperature. This could be attributed to the shift of the composition from stoichiometry which was caused by the high-temperature treatment of the melt.

Time evolution studies of dithieno[3,2-b:2′,3′-d]pyrrole-based A–D–A oligothiophene bulk heterojunctions during solvent vapor annealing towards optimization of photocurrent generation

Solvent vapor annealing (SVA) is one of the main techniques to improve the morphology of bulk heterojunction solar cells using oligomeric donors. In this report, we study time evolution of nanoscale morphological changes in bulk heterojunctions based on a well-studied dithienopyrrole-based A–D–A oligothiophene (dithieno[3,2-b:2 0 ,3 0-d]pyrrole named here 1) blended with [6,6]-phenyl-C 71-butyric acid methyl ester (PC 71 BM) to increase photocurrent density by combining scanning transmission electron microscopy and low-energy-loss spectroscopy. Our results show that SVA transforms the morphology of 1 : PC 71 BM blends by a three-stage mechanism: highly intermixed phases evolve into nanostructured bilayers that correspond to an optimal blend morphology. Additional SVA leads to completely phase-separated micrometer-sized domains. Optical spacers were used to increase light absorption inside optimized 1 : PC 71 BM blends leading to solar cells of 7.74% efficiency but a moderate photocurrent density of 12.3 mA cm A2. Quantum efficiency analyses reveal that photocurrent density is mainly limited by losses inside the donor phase. Indeed, optimized 1 : PC 71 BM blends consist of large donor-enriched domains not optimal for exciton to photocurrent conversion. Shorter SVA times lead to smaller domains; however they are embedded in large mixed phases suggesting that introduction of stronger molecular packing may help us to better balance phase separation and domain size enabling more efficient bulk heterojunction solar cells.