Maiko Hosoda

Characterization of vanadium oxide sol as a starting material for high rate intercalation cathodes

Abstract A novel solution process using vanadium oxide sol with acetone was developed and V2O5/carbon composite cathodes capable of high rate charge/discharge were fabricated. It was found that the sol condition affects the electrochemical performance of the cathodes. This report presents the fabrication process and the electrochemical performance of the cathodes, and the morphological property of the colloidal particle such colloidal particle size, density and shape at various concentrations. The correlation between the electrochemical performance of the cathodes and the colloidal character of the sol is discussed.

Low-Viscosity Measurement by Capillary Electromagnetically Spinning Technique

We study sphere rotation against viscous torque confined in a small space. Our new invention, the electromagnetically spinning sphere (EMS) viscometer measures liquid viscosity through the observation of sphere rotation driven by electromagnetic interaction in a noncontact manner. The lower limit of the measurable viscosity is determined from the ratio between the viscous torque and the mechanical friction, and the apparent increase in the contribution of the viscous term leads to the improvement of the accuracy of low-viscosity measurement. We propose a theoretical expression of the torque applied to a sphere rotating in a cylinder and obtained the power law with respect to the gap in between. The results of the numerical simulation and experiment provide evidence of the validity of the theory.

Accurate Viscosity Measurement of Ethanol Solution for Determination of Ultrasonic Relaxation Parameters

We demonstrate the performance of a newly developed viscosity measurement system, especially designed for liquid samples with low viscosities. The electromagnetically spinning (EMS) viscometer operated with a floating disk rotor enables the determination of viscosity with 1% accuracy for dilute aqueous solutions of various materials. In the article, we report the concentration dependence of the viscosity of a water/ethanol mixture. Accuracy required for a viscometer from the viewpoint of ultrasonic spectroscopy is also discussed.

Doppler Shift of Ripplon Spectrum Observed under Surface Flow

We observed the ripplon spectrum on the flowing liquid surface by the optical beating ripplon light scattering technique. The ripplon spectrum, which is composed of Stokes and anti-Stokes components, is expected to be asymmetric with respect to the center frequency due to the Doppler effect. In the observed spectrum, these two components have clearly different peak frequencies, and the difference agrees well with the value predicted from theoretical calculation. This technique can be applied to the noncontact measurement of the surface flow speed that provides important information on the dynamic adsorption phenomena of surfactant molecules. The sensitivity of the flow speed measurement was also discussed.

Rapid and Precise Measurement System for Ultrasonic Velocity by Pulse Correlation Method Designed for Chemical Analysis

We developed an automatic measurement system for ultrasonic velocity in the megahertz region particularly designed for materials science. The ultrasonic pulse method is fully supported by digital equipment and the correlation function of the 1st and 2nd pulse echoes is numerically obtained from the ultrasonic velocity precisely determined to a relative accuracy of 10-6. An ultrasonic corner reflector is also employed to realize the high reproducibility of the measurement without adjusting the parallelism of the countering transducer and reflector. The performance of the system is examined by determining the concentration dependence of sound velocity in an electrolyte solution in a dilute range.

Observation of Molecular Orientation Induced by Capillary Wave

A new technique was developed for inducing birefringence with the capillary wave in the subsurface region. The capillary wave accompanies a shear viscous flow underneath, and the flow causes a local orientational order of the molecules. The coupling between the shear flow and the molecular orientation can be interpreted in terms of the coupling viscosity µ, which is determined using the present technique. The experiment was carried out in the isotropic phase of 5CB. The observed anisotropy shows the decaying oscillation along the direction of the wave propagation, and the exponential decay into the depth. The measurement was also conducted by cooling the specimen to the critical point of the isotropic-to-nematic phase transition. The birefringence showed a critical behavior toward the virtual transition temperature. The critical exponent for Δn was determined to be 0.8, and that for µ 0.2.

Convergent ellipsometry around Brewster angle for quantitative evaluation of Langmuir films

A new technique of Brewster angle ellipsometry was developed for quantitative evaluation of the Langmuir films extended on water surface. A laser beam with P polarization is focused onto the film with its main axis at the Brewster angle θB. The angular distribution of the reflected light is observed by spatial scan of a photodetector. The scan along the direction of P polarization for the reflected light gives the angular dependence of the reflectivity of P‐polarized light, which has a minimum at θB. The presence of a Langmuir film causes an increase in the minimum reflectivity, from which the quantities such as thickness or density of the adsorbed molecules are obtained. A Langmuir film of stearic acid in its condensed phase was used as a test specimen. The result showed an increase of 2.0×10−6 in the minimum reflectivity, determined accurately to 10−7. The curve of reflectivity was in very good agreement with a prediction by a theory of geometrical optics made with the assumption that the index of refra...

Ultrasonic and Light Scattering Characterization of Anisotropic Colloidal Particles in Sol

We carried out ultrasonic birefringence and dynamic light scattering measurements to estimate the anisotropic shape of particles suspended in an aqueous solution. Since these techniques independently give the hydrodynamic radius and the anisotropy of the particle, we can uniquely determine the anisotropic shape of the ellipsoid particles. The result obtained for TiO2 sol well reproduces the actual shape. However, the model cannot explain the result obtained for the V2O5 sol, suggesting some other soft anisotropic structure of V2O5 particles.

Excitation of elastic and capillary waves by electric field tweezers and its application to material characterization

We recently developed the electric tweezers system to excite the surface vibration for the measurement of local mechanical properties of soft condensed materials. A periodical electric field applied onto the material surface by a conductive thin needle induces the Maxwell stress and picks up the sample surface. We can determine the shear elasticity of the sample from the absolute displacement of the deformation, and the viscosity from its dynamic response, respectively. The numerical simulation predicts that the electric voltage of 100 V applied to the gap of 100 Em between the needle edge and surface induces the deformation of several nm, which was experimentally confirmed by the optical lever technique. The remarkable feature of the system is that the characteristic scale of the surface deformation, such as the depth and width of the medium motion, is dominated by the gap and, therefore, we can uniquely determine the complex mechanical impedance and the surface energy by observing the dynamic surface re...