Shuichi Iwata

Measurement of dynamic surface tension by mechanically vibrated sessile droplets

We developed a novel method for measuring the dynamic surface tension of liquids using mechanically vibrated sessile droplets. Under continuous mechanical vibration, the shape of the deformed droplet was fitted by numerical analysis, taking into account the force balance at the drop surface and the momentum equation. The surface tension was determined by optimizing four parameters: the surface tension, the droplets height, the radius of the droplet-substrate contact area, and the horizontal symmetrical position of the droplet. The accuracy and repeatability of the proposed method were confirmed using drops of distilled water as well as viscous aqueous glycerol solutions. The vibration frequency had no influence on surface tension in the case of pure liquids. However, for water-soluble surfactant solutions, the dynamic surface tension gradually increased with vibration frequency, which was particularly notable for low surfactant concentrations slightly below the critical micelle concentration. This frequency dependence resulted from the competition of two mechanisms at the drop surface: local surface deformation and surfactant transport towards the newly generated surface.

The dynamic motion of single bubbles with unique shapes rising freely in hydrophobically modified alkali-soluble emulsion polymer solutions

The motion of single bubbles rising through hydrophobically modified alkali-soluble emulsion polymer (HASE) solutions is experimentally examined. In this study, we prepare 1.0, 1.1, and 1.6 wt. % HASE solutions and the bubble rise motion is explored depending on the value of the suspending viscosity. Consequently, in a HASE solution with high-viscosity, we find threadlike thin and long branches formed at the trailing edge of the bubble. For moderate-viscosity, we observe bubbles with long and large trailing skirts. These are different from those for Newtonian fluid systems. In the case of low-viscosity, many thread-shaped tails are formed along the bottom edge of the bubble. We observe that threadlike tails irregularly or regularly (unidirectionally) rotate depending on the bubble size along the bottom edge of the bubble. In addition, the bubble rise motion is considered based on modified physical parameters and the terminal bubble rise velocity. In our experimental conditions, it is reported that a jump ...

Evaluation of planar elongation viscosity of low-viscosity liquids using annular abrupt contraction flow around a sliding disk-shaped bob

AbstractThis paper proposes a mechanical measurement technique of the planar elongation viscosity of the low-viscosity liquids. A newly designed flow cell, which consists of a cylindrical cup and a disk-shaped bob with a knife-edged rim, generates the planar elongation flow. Three kinds of Newtonian fluids and an M1 fluid are used. A strain control rheometer pushed the bob into the cup filled with the test fluid and measured the resistant force. The planar elongation viscosity was evaluated using the following two assumptions: first, the resistant force is regarded as the sum of the buoyancy and the resultant forces caused by pressure drops in the planar elongation flow and the shear flow in the test section. Second, the hydraulic mean depth is used as a representative length. The relative errors of the Trouton ratio of the Newtonian fluids were less than 20% compared to the theoretical value of 4. Graphical abstractᅟ

Molecular dynamics study of the molecular mobilities and side-chain terminal affinities of 2-methoxyethyl acrylate and 2-hydroxyethyl methacrylate

Irrespective of the degree of polymerization, the molecular mobilities of the 2-hydroxyethyl methacrylate (HEMA) moieties are smaller than those of the 2-methoxyethyl acrylate (MEA) moieties. Preventing the polar functional groups of the foulants and materials from forming a hydrogen-bonding network is important to enhance the mobilities of the molecular chains of non-ionic polymeric materials. We speculate that enhancing the mobilities of the molecular chains is key to improving blood compatibility.

Rheo-Optic Stress Measurement Between Small Bubbles Under Pressure-Oscillating Field

The rapid elimination of tiny gas bubbles from highly viscous and/or viscoelastic fluids remains a significant challenge. We have proposed a new and effective method (Pressure Oscillating Defoaming; “POD” for short) for increasing the bubble rising velocity in such fluids based on application of an oscillating pressure. A bubble undergoes alternating expansion and contraction under pressure-oscillation field, where the oscillating flow decreases quadratically with the distance from the surface, giving biaxial elongational flow and shear flow in the vicinity of the bubble surface. When two air bubbles are set vertically in a quartz cell filled with shear-thinning fluids, the lower-bubble rises faster than the upper bubble under pressure-oscillating field generated by pressing a rubber sheet at the bottom of the cell. However, this mechanism of the behavior has not been fully understood. By using liquid with a good photoelastic correlation and rheological property similar to the UCM model, we try measuring the stress in the vicinity of small bubbles under pressure-oscillating field. In the case of single bubble, the stress profile measured by the birefringence flow technique was good agreement with stress profile calculated by unsteady state finite element analysis. In this study, retardation profiles were measured near and between the bubbles. In the closer bubble case, the higher retardation profile was observed between the bubbles under pressure-oscillating field.© 2011 ASME

Suspension-Spun High-Tc Oxide Superconducting Filament with High Jc

High Tc oxide supercdonducting filaments with high Jc were successfully prepared using a technique in which suspension spun and subjected to heating treatment. High Jc at 77 K,0 T of more than 10 4 A/cm2 was attained for Tl-(Ba,Sr)-Ca-Cu-O filaments by phase decomposition from 2223 phase to 1223 or 1234 phase, for Bi-Sr-Ca-Cu-O filaments by zone melting and for Y-Ba-Cu-O filament by Quench and Melt Growth process, respectively.